Transgastric Abdominal Ultrasonography in Anesthesia and Critical Care: Review and Proposed Approach : Anesthesia & Analgesia

Secondary Logo

Journal Logo

Review Articles: Narrative Review Article

Transgastric Abdominal Ultrasonography in Anesthesia and Critical Care: Review and Proposed Approach

Denault, André Y. MD, PhD, ABIM-CCM, FRCPC, FASE, FCCS*; Roberts, Michael DO, FASE; Cios, Theodore MD, MPH, FASE; Malhotra, Anita MD; Paquin, Sarto C. MD; Tan, Stéphanie MD§; Cavayas, Yiorgos Alexandros MD, MSc, FRCPC; Desjardins, Georges MD, FRCPC, FASE*; Klick, John MD, FCCP, FASE, FCCM

Author Information
Anesthesia & Analgesia 133(3):p 630-647, September 2021. | DOI: 10.1213/ANE.0000000000005537

Abstract

The use of transesophageal echocardiography (TEE) in the operating room (OR) and intensive care unit (ICU) provides invaluable information on cardiac structures and function to the anesthesiologist and intensivist. There is a growing interest in the use of bedside ultrasound beyond cardiac function.1,2 Such an interest also applies to TEE, but its potential has not yet been fully appreciated by clinicians performing TEE from lack of evidence, limited publication, and training. However, TEE can provide diagnostic and monitoring information of both the anatomy and physiology of the abdominal region, as proposed by Chouinard et al.3

The first description of the use of endoscopic ultrasound dates back to 1980.4,5 Numerous applications for endoscopic ultrasound are currently being used by gastroenterologist sonographers in the diagnosis and treatment of specific abdominal organ pathologies.6,7 However, application of this knowledge to TEE remains challenging. In addition, abdominal TEE is not included in the guidelines for performing a comprehensive TEE examination published by the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists.8 Recent guidelines on the use of TEE to assist with surgical decision-making in the OR suggest a role for abdominal TEE in detecting aortic dissection extension under the diaphragm and inferior vena cava (IVC) stenosis in heart transplantation, artificial heart, and extracorporeal membrane oxygenation.9 For these reasons, significant information on large vessels and abdominal organ function, which can impact on the care of the critically ill patient, may be obtained with TEE, particularly in an intraoperative setting. While not a substitute for the gold standard of transabdominal ultrasound imaging, in contexts such as the OR, abdominal TEE may still provide important information on abdominal organ function and pathology in situations where the standard transabdominal ultrasound views cannot be obtained.

The objective of this review is to gather current knowledge on the relevance of the use of TEE using 10 transgastric (TG) views in the evaluation of the abdominal aorta and related vessels, stomach, liver, kidney, spleen, and pancreas (Table 1). The term TG abdominal ultrasonography, or transgastric abdominal ultrasonography (TGAUS), will be used instead of TEE, because this type of examination does not pertain to the esophagus or the heart. This review will focus on the potential clinical role and method of examination for several reported applications of TGAUS in the OR and ICU (Table 2).

Table 1. - TGAUS Views
TGAUS views N Dual rotating knob position Omniplane (°) Anatomical structure interrogated
Celiac trunk 1 6 o’clock 0–20 Celiac trunk, and hepatic and splenic arteries
SMA-renal confluence 2 6 o’clock 0–20 SMA, SMV, renal arteries, and left renal vein
Gastric 3 12 o’clock 0 and 90 Stomach and peritoneal content
IVC and hepatic veins 4 3 o’clock 0 and 90 IVC, hepatic veins, and peritoneal content
Portal triad 5 3 o’clock 70 ± 20 Portal vein, hepatic artery, and biliary duct
Liver 6 3 o’clock 90a Liver parenchyma and peritoneal content
Spleen 7 9 o’clock 90a Splenic parenchyma and peritoneal content
Kidney 8 9 o’clock 90a Renal parenchyma and adrenal gland
Pancreas 9 6 o’clock 90a Pancreatic parenchyma
Subpancreatic splenic vessels 10 6 o’clock 0–20 Splenic vein and artery
Abbreviations: IVC, inferior vena cava; N, number; SMA, superior mesenteric artery; SMV, superior mesenteric vein; TGAUS, transgastric abdominal ultrasonography.
aTurning the dual rotating knob or axial rotation from left to right to scan the organ.

Table 2. - Clinical Role of TGAUS Views in the Operating Room and Intensive Care Unit
TGAUS views Clinical role
Celiac trunk view 1 and SMA-renal confluence view 2 Vascular monitoring during aortic dissection and vascular stenting3,9–17; detection of compromised splanchnic flow with celiac trunk and mesenteric artery monitoring,13 splanchnic vascular stenosis,18 and nutcracker syndrome19
Stomach view 3 Full stomach, upper gastrointestinal bleeding, gastric varices, and free peritoneal fluid14,20,21
Inferior vena cava and hepatic vein view 4 Diagnosis of right ventricular systolic and diastolic dysfunction,22–30 pulmonary hypertension,31–33 assessment for IVC stenosis in liver transplantation, heart transplantation, ECMO, and artificial heart,9,24,34–42 ruling-out abdominal IVC tumor43–57 or thrombus45,48,56,58–62 as a cause of pulmonary embolism and right-to-left shunting through a PFO in hypoxic patients with right heart dilation,45,48,56,58–61 and abdominal compartment syndrome24,34,63; intraoperative monitoring during renal cell carcinoma surgery involving the inferior vena cava43,45,46,49–53,55,64–74
Portal triad view 5 Abdominal compartment syndrome,20,24,63 mesenteric ischemia with portal venous air,13,20 hepatic artery and portal vein stenosis in liver transplantation,42,62 portal venous Doppler monitoring right ventricular dysfunction associated with venous congestion,14,75–77 and evaluation of response to medical treatment27,78
Liver view 6 Detection of cirrhosis and ascites,14,44 liver abscess or cysts,14 transjugular portal systemic shunt,79 liver transplantation, and resection17,62,79,80
Spleen view 7 Free abdominal fluid and splenic rupture in trauma,20,81 splenic venous Doppler monitoring right ventricular dysfunction associated with venous congestion,14,75–77 and evaluation of response to medical treatment27,78
Kidney view 8 Oligoanuria: renal arterial hypoperfusion or elevate renal resistance index,77,82–90 renal venous congestion,78,83 left hydronephrosis and renal artery air embolization,77 and differentiating acute versus chronic renal failure14
Pancreatic view 9 and subpancreatic splenic vessel view 10 Splenic venous Doppler monitoring right ventricular dysfunction associated with venous congestion14,75–77 and evaluation of response to medical treatment27,78
Abbreviations: ECMO, extracorporeal membrane oxygenation; IVC, inferior vena cava; PFO, patent foramen ovale; SMA, superior mesenteric artery; TGAUS, transgastric abdominal ultrasonography.

In the next sections, we will start by describing the anatomical regions that can be explored using TGAUS, the technique of examination, their relevance in the care of patients undergoing cardiac or noncardiac surgery, and the validation of TGAUS compared to other techniques. We will conclude with the contraindications, complications, future applications, and limitations of TGAUS. Expert opinion from other specialties such as gastroenterology and radiology has been included in our proposed approach to TGAUS examination.

GENERAL PRINCIPLES OF TGAUS EXAMINATION OF THE ABDOMEN

Transabdominal ultrasound typically proceeds by identifying an acoustic window that allows the examination of a selected organ. Transabdominal ultrasound is generally performed using surface ultrasound probes, which is why TGAUS images of splanchnic anatomy are in reversed orientation. The target organ, with its long and short axes, is identified and scanned from left to right and then from top to bottom. Color and pulsed-wave Doppler are used to interrogate vasculature and circulation. The same principles apply to TGAUS with some exceptions, described as follows.

First, the acoustic window is more limited with TGAUS than with transabdominal ultrasound. A different anatomical perspective of the abdominal organs is shown, and only the organs close to the stomach are accessible for TGAUS. Therefore, it is mainly through the stomach wall that the abdominal organs will be examined. Identification of the diaphragm allows the clinician to identify the pleural or abdominal origin of any fluid collections.

Second, examination of the stomach, liver, spleen, kidney, and pancreas can often be limited to longitudinal endoscopic ultrasound examination as performed by gastroenterologists.6,7 Regarding examination of vessels, transverse views or 0° are often sufficient to identify most branches originating from the aorta. However, the orientation of the venous vessels will vary from one organ to the other.

Third, we will be using the official terminology to describe the manipulation of the TEE probe.8 We will also describe the position of the dual rotating knob, because this will have a major impact on the orientation of the image displayed on screen (Supplemental Digital Content 1, Figure 1, Video, https://links.lww.com/AA/D468). When using TGAUS, it is important to separately analyze the displayed image, the orientation of the ultrasound beam (from 0° to 180°), and the position of the ultrasound probe. The displayed image follows the cardiology convention where, in a TG short-axis view of the left ventricle, the left ventricle is displayed on the right side of the screen and the right ventricle on the left. In a TG long-axis view, for instance, the right side of the screen corresponds to the most cephalad organ (left atrium) and the left side of the screen will display the caudal anatomy (left ventricular apex).

The exact position and orientation of the TEE probe must be identified. The TEE probe can be turned from left to right and posteriorly. To describe the turning motion of the probe, we will use the term axial rotation as opposed to the term rotation, which refers to the electronic rotation of the ultrasound beam. The position of the ultrasound beam in the stomach can be determined at the bedside by looking at the position of the dual rotating knob. When TEE is performed in the OR in a supine patient at the head of the bed, the dual rotating knob position can be described in terms of hours in relation to the main axis. For instance, 9 to 10 o’clock or anteriorly is the most common position for a TG short-axis view of the left ventricle, because the heart is anterior to and slightly to the left of a TEE probe located in the stomach. As abdominal organs will be examined through the stomach, their position will not always be anterior to the TEE probe (Figure 1A–D). Some organs will be on the left side, such as the spleen and left kidney. Others will be posterior, such as the abdominal aorta and the pancreas, while the liver will be viewed on the right side of the stomach. As the TEE probe is turned or axially rotated to the right, to the left, or posteriorly, the orientation of the images displayed on the screen showing a long-axis or 90° view will remain unchanged: caudal structures will appear on the left portion of the screen. The right portion of the screen will display the cephalad anatomy regardless of the orientation of the ultrasound beam (Figure 1E–H). The orientation of the images obtained with a transverse or 0° view will be modified as the TEE probe is axially rotated from left to right. Any axial rotation of the TEE probe will modify the displayed orientation of the transverse images (Figure 1A–D). When the TEE probe is turned posteriorly at 6 o’clock, for instance (Figure 1C), the left side of the screen will display left-sided anatomical structure and the right portion of the screen, right-sided structures. The 2 basic TG TEE views will be taken as reference or initiation points to perform TGAUS. By combining them, the organ can be scanned from left to right and then from top to bottom.

F1
Figure 1.:
TGAUS probe orientation in a supine patient with the TGAUS probe at the head of the patient. A, The dual rotating knob is positioned anteriorly at 12 o’clock. The ultrasound beam is at 0°. On a corresponding 2D image, the right side of the screen (red line) corresponds to the left anterior anatomical structures and the left side of the screen (green line) corresponds to the right anterior anatomical structures. B, The dual rotating knob is positioned to the right at 3 o’clock. The ultrasound beam is at 0°. On a corresponding 2D image, the right side of the screen (red line) corresponds to the right anterior anatomical structures and the left side of the screen (green line) corresponds to the right inferior anatomical structures. C, The dual rotating knob is positioned at the back of the patient, posteriorly at 6 o’clock. The ultrasound beam is at 0°. On a corresponding 2D image, the right side of the screen (red line) corresponds to the right inferior anatomical structures and the left side of the screen (green line) corresponds to the left inferior anatomical structures. D, The dual rotating knob is positioned to the left of the patient at 9 o’clock. The ultrasound beam is at 0°. On a corresponding 2D image, the right side of the screen (red line) corresponds to the left inferior anatomical structures and the left side of the screen (green line) corresponds to the left superior anatomical structures. E, The dual rotating knob is positioned anteriorly at 12 o’clock. The ultrasound beam is at 90°. On a corresponding 2D image, the right side of the screen (red line) corresponds to the anterior cephalad anatomical structures and the left side of the screen (green line) corresponds to the anterior caudal anatomical structures. F, The dual rotating knob is positioned to the right at 3 o’clock. The ultrasound beam is at 90°. On a corresponding 2D image, the right side of the screen (red line) corresponds to the right cephalad anatomical structures and the left side of the screen (green line) corresponds to the right caudal anatomical structures. G, The dual rotating knob is positioned in the back of the patient, posteriorly at 6 o’clock. The ultrasound beam is at 90°. On a corresponding 2D image, the right side of the screen (red line) corresponds to the inferior cephalad anatomical structures and the left side of the screen (green line) corresponds to the inferior caudal anatomical structures. H, The dual rotating knob is positioned to the left of the patient at 9 o’clock. The ultrasound beam is at 90°. On a corresponding 2D image, the right side of the screen (red line) corresponds to the left cephalad anatomical structures and the left side of the screen (green line) corresponds to the left caudal anatomical structures. TGAUS indicates transgastric abdominal ultrasonography. Artwork from Hugo Babin (Supplemental Digital Content 1, Figure 1, Video, https://links.lww.com/AA/D468).
Table 3. - Doppler Arterial Velocities of Abdominal Vessels Accessible With TGAUS
Artery Peak systolic velocity (cm/s) Resistance indexa Comment/references
Celiac trunk 113 ± 17.5 0.6–0.8 Stenosis if >200 cm/s91–94
<200
Hepatic artery 30–40 0.5–0.8 AT <100 ms93,94
Splenic artery 100 0.5–0.7 91,95
Superior mesenteric artery 100–140 >0.8 fasting Low or reversed diastolic velocity in fasting state92,94
Stenosis if >275 cm/s93
Renal artery 52 ± 20 0.56–0.7 AT <57 ms83,91,93,94
<150 Stenosis if >180 cm/s94
Abbreviations: AT, acceleration time; TGAUS, transgastric abdominal ultrasonography.
a(Systolic velocity-diastolic velocity)/systolic velocity.

F2
Figure 2.:
TGAUS views. Ao indicates aorta; HV, hepatic vein; IVC, inferior vena cava; LHV, left hepatic vein; LRA, left renal artery; LRV, left renal vein; MHV, middle hepatic vein; RHV, right hepatic vein; RPV, right portal vein; RRA, right renal artery; SA, splenic artery; SMA, superior mesenteric artery; SMV, superior mesenteric vein; SV, splenic vein; TGAUS, transgastric abdominal ultrasonography.

We propose 10 TGAUS views based on the most commonly reported applications for this modality (Supplemental Digital Content 2, Table 1, https://links.lww.com/AA/D469). They are summarized in Table 1 and illustrated in Figure 2. Corresponding arterial Doppler velocities are summarized in Table 3. Supplemental Digital Content 3, Figure 1, https://links.lww.com/AA/D470, illustrates the most important upper abdominal organs and the vascular anatomy that can be examined using TGAUS using simulators and 3D reconstruction. These include the aorta and its branches, stomach, liver, hepatic vein and artery, portal vein, spleen, kidneys, and pancreas.

Abdominal Vasculature

One of the goals of perioperative TEE is the assessment of aortic disease, such as trauma, dissection, aneurysm, and congenital anomalies. TEE is used to more accurately identify the site of disease in the descending thoracic aorta, but it can also identify the abdominal aorta using the celiac artery as an anatomical marker or a division point between the thoracic and abdominal aortas.10

TGAUS Examination Technique for Celiac Trunk View 1 and SMA-Renal Confluence View 2.

TGAUS Celiac Trunk View 1.
F3
Figure 3.:
A, Transgastric abdominal ultrasonography view at 0° with color Doppler (Nyquist 16–22 cm/s) shows the CT in relation to the Ao and its division into the hepatic and splenic artery. B and C, Anatomical representation using the Vimedix simulator and (D) corresponding computed tomographic scanning. A. indicates artery; Ao, aorta; CT, celiac trunk. Courtesy of CAE Healthcare, Canada, for subparts B (Supplemental Digital Content 4, Video View 1, https://links.lww.com/AA/D471).

To examine the celiac trunk, the TGAUS probe is advanced from the thoracic aorta beyond the crux of the diaphragm at a transducer angle of 0° into a TG short-axis left ventricular view. At this point, the TGAUS probe is gradually rotated so that the TGAUS dual rotating knob is typically oriented downward in a 6 o’clock position. As the probe is advanced into the stomach, the aorta should be kept in view. As the probe is advanced, the celiac artery will be seen first followed by the superior mesenteric arteries (SMAs) at 1 and 3 o’clock, respectively. The celiac artery branches into the splenic and hepatic arteries, while the SMA stays adjacent to the aorta. The celiac artery is the first major branch of the descending aorta (Figure 3; Supplemental Digital Content 4, Video View 1, https://links.lww.com/AA/D471). To identify blood velocities, the operator must lower the Nyquist limit from the cardiac preset of 55–65 to 20–30 cm/s. The celiac trunk can easily be visualized using color Doppler because of its larger diameter (7.8 ± 0.5 mm) and more cephalad position compared to the SMA.3,11 The normal velocity of the celiac trunk is 113 ± 17.5 cm/s.91,92 The celiac trunk can be imaged with TGAUS in 81% to 100% of patients.12,82

TGAUS SMA-Renal Confluence View 2.

The second vessel after the celiac trunk is the SMA (Supplemental Digital Contents 5–8, Figures 2 and 3, Video View 2, https://links.lww.com/AA/D472, https://links.lww.com/AA/D473, https://links.lww.com/AA/D474, https://links.lww.com/AA/D475). It can be identified in a similar manner, namely, by advancing the probe into the stomach beyond the celiac artery view with a Nyquist limit set at 20 to 30 cm/s. The SMA may be distinguished from the celiac trunk by the absence of its distal bifurcation into the hepatic and splenic arteries. The SMA is typically located between the superior mesenteric vein and the left renal vein (Supplemental Digital Contents 3, 5, and 7, Figures 1E and 2A, Video View 2, https://links.lww.com/AA/D470, https://links.lww.com/AA/D472, https://links.lww.com/AA/D474). As the probe is further advanced, the left renal vein will appear between the SMA and the aorta. The right renal artery will appear on the screen at 4 o’clock, and the left renal artery will appear at 10 o’clock caudal to the SMA. The SMA normal velocity is 145 ± 25.8 cm/s.92 The SMA can be imaged with TGAUS in 95.2% of patients.12 The splenic, hepatic, and renal arteries are discussed in the following sections.

Clinical Applications

The ability to precisely locate aortic disease and its impact on visceral branches may be of use during aortic repair procedures, especially in aortic dissections and aneurysms. In addition, TGAUS may help detect any stenosis of major aortic visceral branch vessels (Supplemental Digital Contents 9–11, Figure 4, Video View 1, https://links.lww.com/AA/D476, https://links.lww.com/AA/D477, https://links.lww.com/AA/D478).3 Celiac trunk stenosis is present if peak velocities are >200 cm/s.93 TGAUS was used to identify celiac artery stent thrombosis in critically ill patients who are unable to receive contrast due to acute renal failure.10

SMA blood velocities can be monitored with TGAUS during cardiopulmonary bypass (CPB). In aortic dissection, mesenteric ischemia can occur with obstruction of the SMA by the aortic false lumen or intimal flap. Narrowing of >50% of the SMA or absence of the color Doppler velocity signal can be indicative of malperfusion.13 Elevated SMA peak velocities >275 cm/s are highly suggestive of stenosis.18,93 Mesenteric ischemia after cardiac surgery is a complication with high morbidity and mortality.96 Guidelines from the American Society of Echocardiography in 2020 on the use of TEE to assist for surgical decision-making mentioned that TEE should be used to identify the presence of the dissection flap down to the subdiaphragmatic descending aorta.9 Dissection could happen, for instance, during endovascular aortic procedures and would lead to surgical or angiographic intervention. Because of the location of the SMA, compression of the left renal vein can occur between the SMA and the abdominal aorta, leading to left renal venous congestion, which can also be diagnosed with TGAUS.78,97 This phenomenon is called the “nutcracker syndrome.” Intraoperative recognition of this phenomenon could allow surgical or catheter-based intervention.

Stomach

Cardiac examination is routinely done from the stomach when performing TEE using a TG short- or long-axis view (Supplemental Digital Contents 12–15, Figure 5, Video View 3, https://links.lww.com/AA/D479, https://links.lww.com/AA/D480, https://links.lww.com/AA/D481, https://links.lww.com/AA/D482).

TGAUS Examination Technique for Stomach View 3

The stomach anatomy can be examined in both short- and long-axis views. When advancing the probe in short axis, the operator will be able to view the fundus followed by the antrum (Supplemental Digital Contents 12–15, Figure 5, Video View 3, https://links.lww.com/AA/D479, https://links.lww.com/AA/D480, https://links.lww.com/AA/D481, https://links.lww.com/AA/D482). In a long-axis view, a leftward axial rotation of TGAUS will reveal the spleen behind the fundus (Supplemental Digital Contents 12 and 14, Figure 5C, Video View 3, https://links.lww.com/AA/D479, https://links.lww.com/AA/D481). No echo-free space suggestive of fluid in the peritoneal space should be seen anterior to the stomach wall or between the stomach and the spleen.

Clinical Applications

If free peritoneal bleeding is present in hemodynamically unstable patients, it may be identified by TGAUS between the stomach, the left lobe of the liver, and the heart (Supplemental Digital Contents 12 and 15, Figure 5E, Video View 3, https://links.lww.com/AA/D479, https://links.lww.com/AA/D482).14 Studies have shown that transabdominal ultrasound can be used to estimate stomach volume and consequently the risk of aspiration.98 In emergency settings, TGAUS examination can detect an empty stomach (Supplemental Digital Contents 16 and 17, Figure 6A, Video View 3, https://links.lww.com/AA/D483, https://links.lww.com/AA/D484) and, sometimes as an incidental finding, a full stomach with clear liquid (Supplemental Digital Contents 16 and 18, Figure 6B, Video View 3, https://links.lww.com/AA/D483, https://links.lww.com/AA/D485), blood or blood clot (Supplemental Digital Contents 16 and 19, Figure 6C, Video View 3, https://links.lww.com/AA/D483, https://links.lww.com/AA/D486), solid food (Supplemental Digital Contents 16 and 20, Figure 6D, Video View 3, https://links.lww.com/AA/D483, https://links.lww.com/AA/D487), gastric varices using color or power Doppler (Supplemental Digital Contents 16 and 21, Figure 6E, Video View 3, https://links.lww.com/AA/D483, https://links.lww.com/AA/D488), and severe gastric and bowel edema often associated with right heart failure99 (Supplemental Digital Contents 16 and 22, Figure 6F, Video View 3, https://links.lww.com/AA/D483, https://links.lww.com/AA/D489). However, contrary to the transabdominal approach, an accurate estimation of the amount of gastric fluid using TGAUS has not yet been validated.98,100

Liver

The liver and its vessels, which include the hepatic vein, portal vein, and hepatic artery, are easily examined by TGAUS. The intrahepatic bile ducts can occasionally be seen in patients after cholecystectomy, without elevated serum bilirubin.

TGAUS Examination Technique for IVC and Hepatic Veins View 4, Portal Triad View 5, and Liver View 6

TGAUS examination of the liver starts with the identification of the IVC. As mentioned by Hahn et al,8 the IVC is located in the retroperitoneal space, to the right of the vertebral body and abdominal aorta.

TGAUS IVC and Hepatic Vein View 4

From a TG short-axis view of the left ventricle, the probe is rotated to the patient’s right, where the dual rotating knob will be at 3 o’clock. The IVC and the hepatic veins should be identified. The IVC and the 3 hepatic veins (left, middle, and right) can be examined at a transducer angle of 0° (Supplemental Digital Contents 23–25, Figure 7, Video View 4, https://links.lww.com/AA/D490, https://links.lww.com/AA/D491, https://links.lww.com/AA/D492) or using a midesophageal bicaval view at 90°. In the latter case, only 1 hepatic vein will be identified at a time. Sequential identification of the hepatic veins can be done and facilitated using color Doppler at a Nyquist limit of 30 to 40 cm/s when rotating the TEE probe from left to right.8,101,102 To identify the hepatic vein confluence with the IVC, Blinn et al43 proposed the use of an ultrasound orientation of 40° to 70°, 50° to 90°, and 80° to 130° for the right, middle, and left hepatic veins, respectively. A normal hepatic vein diameter is 7.3 ± 1.3 mm,103 with triphasic mean systolic, diastolic, and atrial reversal velocities of 21.3 ± 13.9, 15 ± 9.5, and 7.5 ± 5.2 cm/s, respectively.104 The right, middle, and left hepatic vein Doppler tracings can be obtained with TGAUS in 100%, 97%, and 18% of patients, respectively.102

TGAUS Portal Triad View 5

The portal vein can be evaluated by TGAUS by rotating the probe toward the patient’s right side with the dual rotating knob at 3 o’clock, and a longitudinal view of the IVC can be obtained at 90° with further insertion of the probe into the stomach. A multiplane angle of 50° to 70° will align the right portal vein. Using a Nyquist limit of 20 cm/s, color and pulsed-wave Doppler can be applied to interrogate the portal vein and hepatic artery (Supplemental Digital Contents 26–28, Figure 8A, Video View 5, https://links.lww.com/AA/D493, https://links.lww.com/AA/D494, https://links.lww.com/AA/D495). The portal vein (diameter of 10.5 ± 1.7 mm),103 which is downstream from the splenic and the superior mesenteric vein (Supplemental Digital Content 26, Figure 8C, https://links.lww.com/AA/D493), can be identified by its echodense sheath, and a typical laminar or monophasic velocity between 16 and 31 cm/s (Supplemental Digital Contents 26 and 27, Figure 8B, Video View 5, https://links.lww.com/AA/D493, https://links.lww.com/AA/D494).93 The hepatic artery can be seen in proximity to the portal vein or identified also as the right-sided bifurcation of the celiac trunk (common hepatic artery) (Figure 3; Supplemental Digital Content 4, Video View 1, https://links.lww.com/AA/D471), as described previously. The portal vein Doppler tracing can be obtained with TGAUS in 94% of patients.75

TGAUS Liver View 6

To examine the whole liver from a longitudinal view, the TEE probe has to be rotated to the patient’s right with the dual rotating knob at 3 o’clock and advanced at the origin of the IVC (Supplemental Digital Contents 29–32, Figure 9, Video View 6, https://links.lww.com/AA/D496, https://links.lww.com/AA/D497, https://links.lww.com/AA/D498, https://links.lww.com/AA/D499). By scanning from the left lobe to the right lobe of the liver, it is possible to evaluate the liver texture. The texture of a normal liver should be homogeneous, with no echo-free space between the liver, diaphragm, and stomach. Apart from the position of the left, middle, and right hepatic veins, there are no precise ultrasound landmarks to identify the transition point from the left to the right lobe of the liver. Although evaluation of the whole liver is beyond the scope of TGAUS evaluation, by performing an axial rotation of the probe beginning at the median side of the left lobe of the liver toward the right, it is possible to analyze part of the parenchyma, mainly the left lobe, with only a section of the right lobe.44

Clinical Applications

Examination of the IVC can be used in determining the etiology of hemodynamic instability and hypoxemia. For instance, TGAUS can detect IVC thrombus (Supplemental Digital Contents 29 and 30, Figure 9B, Video View 6, https://links.lww.com/AA/D496, https://links.lww.com/AA/D497), which is particularly common after extracorporeal membrane oxygenation weaning.105 Such thrombus can lead to pulmonary emboli, right ventricular failure, and, in some patients, paradoxical emboli through a patent foramen ovale.106 Spontaneous contrast in the IVC can be observed in patients with right ventricular dysfunction and cardiac tamponade (Supplemental Digital Contents 29 and 31, Figure 9C, D, Video View 6, https://links.lww.com/AA/D496, https://links.lww.com/AA/D498). Hemoperitoneum can be diagnosed when free fluid is present at the level of the left hepatic lobe, between the stomach and the heart (Supplemental Digital Contents 12 and 15, Figure 5E, Video View 3, https://links.lww.com/AA/D479, https://links.lww.com/AA/D482). Several authors have also reported on the role of TGAUS in managing patients with renal tumor extending to the IVC,43,45–49,58–61,64 which is discussed in the following section. The hepatic venous velocity patterns can give insight into hepatic perfusion as well as right heart dynamics.22,23,44 Monitoring of hepatic venous velocities in humans,101 as well as in experimental animal models107 undergoing laparoscopic cholecystectomy, has shown that positive end-expiratory pressure and elevated intraabdominal pressure have adverse effects on overall splanchnic velocities.101,107 Blunting or reversal of the systolic forward flow velocities through the hepatic venous system may be a marker of either right ventricular diastolic dysfunction or severe tricuspid regurgitation,44,102,104 and absence of a biphasic hepatic signal or blunted velocities may indicate IVC stenosis24 or resistance to venous return.34 This can occur in any procedure in which the IVC is surgically manipulated or anastomosed, as in a Fontan procedure (Supplemental Digital Contents 33 and 34, Figure 10, Video View 6, https://links.lww.com/AA/D500, https://links.lww.com/AA/D501),108 orthotopic heart transplantation,24 or liver transplantation.24,35 The abnormal aspect of the hepatic venous velocity is similar to pulmonic vein stenosis in lung transplantation with loss of systolic and diastolic flow.9 This can lead to venous hypertension, as well as liver and renal failure.36 Hemodynamically compromised anastomotic stricture and extrinsic compression of the IVC have been detected by TGAUS, allowing for rapid intervention.37,62 Hepatic vein evaluation may also be of use during noncardiac surgical procedures such as transjugular intrahepatic portosystemic shunt placement.44 In these patients, their shunts can be examined by TGAUS (Supplemental Digital Content 35, Figure 11, https://links.lww.com/AA/D502). Maximum velocities through the shunt >190 or <90 cm/s may indicate shunt occlusion, which may place the patient at risk for variceal bleeding and hepatic dysfunction—both significant concerns in the perioperative setting.44,79

Careful examination of portal venous velocity with color and pulsed-wave Doppler may also assist in the assessment of right heart function, which can lead to hepatic venous congestion.75,76 This can be done by interrogation of the portal vein or splenic vein just caudal to the pancreas (see the following). Normal portal venous velocity is typically laminar. However, elevated right atrial pressure may transmit retrograde through the IVC and portal venous system, which will decrease forward systolic flow velocity and cause a pulsatile pulsed-wave Doppler spectral profile (Supplemental Digital Content 29, Figure 9D, https://links.lww.com/AA/D496). This pattern and even flow reversal can also be observed in cirrhosis and portal hypertension.109 Portal vein pulsatility index (PVPI) can be calculated as the ratio of maximal and minimal velocity ([Vmax − Vmin]/Vmax). An association has been observed between PVPI >0.5 and high right atrial pressure, moderate or greater tricuspid regurgitation, and right ventricular dysfunction.75,110 More recently, PVPI has been linked to cardiorenal syndrome and acute kidney injury after cardiac surgery.111,112 Eljaiek et al75 previously reported that an intraoperative PVPI ≥0.5 measured with TGAUS was the most important predictor of postoperative complications after cardiac surgery in 115 cardiac surgical patients; it was also determined as superior to any hemodynamic, 2D, and Doppler cardiac measurement. An international multicenter study (NCT03656263) is currently exploring the clinical significance of portal hypertension after cardiac surgery. Finally, air resulting from intestinal ischemia can be present in the portal vein of hemodynamically unstable patients (Supplemental Digital Contents 36 and 37, Figure 12, Video View 5, https://links.lww.com/AA/D503, https://links.lww.com/AA/D504).13,20 The absence of a portal velocity signal in a patient in shock has been reported in abdominal compartment syndrome.24

Hepatic artery Doppler velocities can be used to assess hepatic perfusion and anastomosis after liver transplantation.113 Changes in hepatic artery Doppler velocities and resistance indices are influenced by the severity of cirrhosis and portal hypertension.109 In cardiac surgery, Gårdebäck et al22 were able to demonstrate a 50% reduction in hepatic blood velocities during hypothermic CPB using TGAUS as the primary method of monitoring. No reduction was observed in normothermic CPB. Careful examination of the liver may also give rise to new and important diagnoses. Heterogeneous appearance of the liver parenchyma is suggestive of cirrhosis or chronic liver disease, whereas the detection of focal lesions may cause suspicion of neoplasm or liver abscess.44 In unstable patients, free fluid between the liver and the diaphragm can indicate the presence of a hemoperitoneum or be suggestive of ascites. They should be followed by paracentesis if suspicion of spontaneous bacterial peritonitis is raised (Supplemental Digital Contents 29 and 30, Figure 9, Video View 6, https://links.lww.com/AA/D496, https://links.lww.com/AA/D497).

Spleen

The spleen is located on the left side of the stomach. The upper pole sits under the diaphragm, while the lower pole sits at the splenic flexure of the colon.

TGAUS Examination Technique for Splenic View 7

Using a 2-chamber TG TEE view, a leftward axial rotation of the TEE probe with dual rotating knob at 9 o’clock will enable identification of the spleen (Supplemental Digital Contents 38–43, Figure 13, Video View 7, https://links.lww.com/AA/D505, https://links.lww.com/AA/D506, https://links.lww.com/AA/D507, https://links.lww.com/AA/D508, https://links.lww.com/AA/D509, https://links.lww.com/AA/D510). A leftward axial rotation of the ultrasound probe will then display the complete homogenous anatomical structure. TGAUS imaging of the splenic artery and vein can be obtained from a TG view by rotating to the left and changing the omniplane angle to 90°.34 The splenic vein and artery can be evaluated with color Doppler using a Nyquist limit of 30 cm/s for the interrogation of the splenic hilum. The normal maximal splenic vein velocity is 27 ± 4 cm/s and is typically monophasic.114 The splenic vein position under the pancreas is described in the following. The splenic artery can also be identified as a branch of the celiac artery as described previously (Figure 3; Supplemental Digital Content 4, Video View 1, https://links.lww.com/AA/D471). The maximal arterial Doppler velocity is 100 cm/s.91,95 Pulsed-wave Doppler is placed 1 cm into the artery from the hilum, and the splenic arterial Doppler resistive index can be calculated as (splenic resistance index = [peak systolic velocity − end-diastolic velocity]/peak systolic velocity).

Clinical Applications

Splenomegaly should be suspected when the spleen is noted to extend beyond the left kidney, with normal dimensions: longitudinal: 12 to 14 cm, lateral: <5 cm, and anteroposterior: <7 cm. The longitudinal measurement of the spleen is limited by the maximal width of the TGAUS beam, with the probe being close to the organ. Free peritoneal fluid (Supplemental Digital Contents 38, 42, and 43, Figure 13D, E, Video View 7, https://links.lww.com/AA/D505, https://links.lww.com/AA/D509, https://links.lww.com/AA/D510) and splenic rupture may be detectable using TGAUS in the setting of a traumatic injury or surgical complication (Supplemental Digital Content 38, Figure 13F, https://links.lww.com/AA/D505).14,81 Splenic vein interrogation at the hilum will provide similar information to the portal vein in terms of right ventricular dysfunction. Splenic arterial Doppler will also be influenced by any stenosis beyond its origin, identified by abnormal aliasing on color Doppler or elevated velocities on spectral Doppler (Supplemental Digital Content 9, Figure 4C, https://links.lww.com/AA/D476). The presence of right heart failure will lead to an increase in the splenic vein pulsatility index ([peak systolic velocity − end-diastolic velocity]/peak systolic velocity).103 Finally, changes in the resistance index of the splenic artery have been validated as a method to evaluate fluid responsiveness95,109 similar to the renal resistance index (RRI).115 A <4% reduction in the splenic Doppler resistance index generally excludes fluid responsiveness in mechanically ventilated patients, while >9% splenic Doppler resistance index reduction indicates fluid responsiveness.95

Kidneys

The left kidney lies posterior and inferior to the spleen and can be visualized during TGAUS. Doppler examination of renal artery blood flow velocity confirms the presence of renal flow, which may be a concern during aortic surgery, as well as allows for the calculation of RRI. In one-third of kidneys, >1 renal artery might be present.91

TGAUS Examination Technique for Kidney View 8

Chouinard et al3 first described TEE examination of the kidneys in 1991, and then Yang et al83 and Bandyopadhyay et al84 described their examination protocol by using color Doppler to visualize renal perfusion and the renal parenchyma. The examination should start with a TG left ventricular long-axis view with left-sided axial rotation of the dual rotating knob up to 9 o’clock. In our experience, as the kidney is just behind the spleen, further axial rotation of the TGAUS probe at an imaging plane of 90° is often enough to image the left kidney. Contrary to the spleen, the kidney has an outer cortex and inner medulla surrounded by the hyperechogenic Gerota fascia (Supplemental Digital Contents 44 and 45, Figure 14A, Video View 8, https://links.lww.com/AA/D511, https://links.lww.com/AA/D512). To calculate the maximal longitudinal diameter, it is possible to advance multiplane angle rotation to 120° to 140°. The normal renal size is 10 to 12 cm on its long axis. Then, as with other organs, a rightward to leftward axial rotation allows for a more complete examination of the left kidney. The use of TGAUS to image the right kidney using a TG short-axis view has been reported in adults and in children.85,86 In our experience, it is difficult to identify the right kidney given its location further from the stomach. Once the 2D examination is complete, interrogation of the arterial and venous circulation can be done using Doppler at a Nyquist limit of 10 cm/s. This low-velocity limit is important to identify the venous velocities.78 On certain systems, low-velocity filters have to be removed before interrogation. The short-axis view at the level of the aorta is also useful in the identification of the 2 renal arteries, renal vein, SMA, splenic vein, and artery (Supplemental Digital Contents 5–8, Figures 2 and 3, Video View 2, https://links.lww.com/AA/D472, https://links.lww.com/AA/D473, https://links.lww.com/AA/D474, https://links.lww.com/AA/D475). The renal artery and vein diameters are 4.0 ± 0.9 and 8.1 ± 2.90 mm, respectively.83 The renal artery Doppler velocities are typically 52 ± 20 cm/s with a rapid upstroke.83,91,93 Pulsed-wave Doppler can be applied to an interlobar artery to examine peak systolic and end-diastolic velocities, which can be used to calculate RRI (RRI = [peak systolic velocity − end-diastolic velocity]/peak systolic velocity).3,84,85 Normal renal venous Doppler velocities obtained with TGAUS83 are typically laminar, continuous, and <20 cm/s.116 Right renal artery velocities are obtainable in approximately 56% to 88% of patients12,82,86 and left renal artery in 15% to 67% of patients.12,82,83

Clinical Applications

Because fibrous tissue (eg, glomerulosclerosis and interstitial fibrosis) increases echogenicity, chronic kidney disease is typically associated with increased echogenicity and reduction in size. The contrast between the cortex and medulla disappears. TGAUS can diagnose hydronephrosis or renal cysts (Supplemental Digital Contents 44 and 46, Figure 14D, Video View 8, https://links.lww.com/AA/D511, https://links.lww.com/AA/D513). The RRI may be of particular interest in patients at risk of renal dysfunction, as elevated values (>0.7) have been shown to be associated with an increased risk of acute kidney injury in cardiac surgical patients,117–119 although it can be falsely elevated in patients with aortic insufficiency.87 Aspects of the arterial renal Doppler profile can also be diagnostic of certain pathological conditions. For instance, a tardus parvus spectral profile can be seen with renal artery stenosis or aortic stenosis (Supplemental Digital Content 48, Figure 15A, https://links.lww.com/AA/D515). In addition, renal venous congestion can be diagnosed using Doppler interrogation at the corticomedullary junction. Three patterns have been described: normal continuous, biphasic, and monophasic patterns (Supplemental Digital Contents 48, 51, and 52, Figures 15B and 16, Video View 8, https://links.lww.com/AA/D515, https://links.lww.com/AA/D518, https://links.lww.com/AA/D519).112,116,120 The renal venous Doppler profiles change in parallel with the increase in right atrial pressure and the severity of right ventricular dysfunction.78,112,116,120 The biphasic and monophasic patterns have been associated with increased mortality in heart failure116,121 and postoperative renal failure in cardiac surgery.78,112 Finally, during cardiac surgery, air emboli can be detected in the renal vessels that could contribute to postoperative renal dysfunction (Supplemental Digital Contents 48–50, Figure 15C, D, Video View 8, https://links.lww.com/AA/D515, https://links.lww.com/AA/D516, https://links.lww.com/AA/D517).

In addition, TGAUS can also assist in the diagnosis and surgical management of renal cell carcinoma (Supplemental Digital Contents 44 and 47, Figure 14E, F, Video View 8, https://links.lww.com/AA/D511, https://links.lww.com/AA/D514), from which IVC involvement can occur in 4% to 10% of cases.65 Traditionally, these tumors may require complicated resections involving sternotomy, CPB, and even deep hypothermic circulatory arrest with significant morbidity and mortality rates.46,65,122 TGAUS can be used to monitor the burden of thrombus and possible propagation/migration to the right atrium during surgery with IVC thrombectomy and reconstruction. Some authors have suggested that TGAUS can provide real-time assessment of the mobility, fragility, and degree of IVC invasion by the tumor or risk of embolization into the right atrium using the Neves and Zincke classification of renal cell carcinoma.43,45,50,51,66,123,124 Tumors can evolve between the time of preoperative testing and the day of surgery; TGAUS is, therefore, considered an important tool to accurately locate the tumor intraoperatively, which will improve surgical planning,50,52,67,68 as well as guide and direct69 catheter-guided49 or robot-assisted thrombectomy.70 Tumor resection may require clamping of the IVC, which dramatically affects preload. TGAUS is also a useful tool to differentiate hypotension due to changes in preload versus tumor embolization with resulting right ventricular failure and obstructive shock.51,67 Once the resection is complete, TGAUS can also be used to carefully examine the IVC for any residual tumor.67 The intraoperative guidance afforded by TGAUS may allow for a less invasive catheter-based cavoatrial thrombectomy, thus sparing the patient from sternotomy, CPB, and its associated complications.50,71,72

Pancreas

The pancreas sits behind the stomach. The pancreatic body lies anterior to the aorta and the pancreatic head is located to the right of the portal vein. The pancreatic body and tail are located to the left of the portal vein, with the body approximately between the portal vein and left kidney and the tail approximately between the left kidney and the spleen. A lesion in the head versus body-tail can greatly impact management (eg, Whipple surgery versus distal body-tail pancreatectomy). However, the exact distinction between pancreatic body and tail does not significantly impact management. Recognition of the splenic artery and vein helps locate the pancreatic body, because these vessels travel along its length. Normal pancreatic texture is isoechoic with dimensions of head (3 cm), body (2–3 cm), and tail (1–2 cm).14

TGAUS Examination Technique for Pancreatic View 9 (Pancreas) and Subpancreatic Splenic Vessels View 10.

TGAUS Pancreatic View 9.

The examination of the pancreas is similar to the other abdominal structures. The TGAUS probe is turned to the patient’s back with the dual-rotating knob at 6 o’clock, using a longitudinal plane and scanning from the spleen hilum to the head of the pancreas (Supplemental Digital Contents 53 and 55, Figure 17A, B, Video View 9, https://links.lww.com/AA/D520, https://links.lww.com/AA/D522). The pancreas sits between the TGAUS probe and the splenic vein. Using color Doppler at a Nyquist limit of 20 cm/s, both the splenic vein and splenic artery can be visualized in a short-axis view.

TGAUS Subpancreatic Splenic Vessels View 10.

The splenic vessels can be more easily visualized and interrogated using a short-axis view. By turning the dual rotating knob at 6 o’clock, the aorta and celiac trunk can be identified (Figure 3; Supplemental Digital Content 4, Video View 1, https://links.lww.com/AA/D471). A slight axial rotation of the dual rotating probe toward the celiac bifurcation will allow the identification of the splenic artery. Color Doppler is then turned on using a Nyquist limit of 20 cm/s. Slowly advancing the probe shows the splenic vein, which is optimally oriented for Doppler interrogation (Supplemental Digital Contents 53 and 56, Figure 17C, Video View 10, https://links.lww.com/AA/D520, https://links.lww.com/AA/D523). The success rate of obtaining TGAUS views 9 and 10 is >90% of the time, similar to the portal vein.75,76

Clinical Applications

The splenic artery can easily be monitored intraoperatively from a pancreatic view or just after the bifurcation of the celiac trunk (Figure 3; Supplemental Digital Content 4, Video View 1, https://links.lww.com/AA/D471), and its role has been described before in TGAUS View 8. Splenic artery air emboli can be monitored and detected from this position (Supplemental Digital Contents 9 and 11, Figure 4D, Video View 1, https://links.lww.com/AA/D476, https://links.lww.com/AA/D478). The splenic vein reaches the portal vein (Supplemental Digital Content 26, Figure 8C, https://links.lww.com/AA/D493) and, therefore, yields similar information in terms of right ventricular dysfunction and splanchnic venous congestion (Supplemental Digital Contents 57–59, Figure 18, Video View 10, https://links.lww.com/AA/D524, https://links.lww.com/AA/D525, https://links.lww.com/AA/D526).14,76

VALIDATION OF TGAUS

Information about 2D anatomy and Doppler velocity of specific abdominal organs can be provided using TGAUS. Because TGAUS uses a high-resolution 7.5-MHz probe, the spatial resolution will be higher with a 0.2-mm wavelength than a transabdominal ultrasound using a 3.75-MHz probe with a 2.4-mm wavelength. This resolution provides more precise information for structures near the probe, similar to the comparison between TEE and TTE imaging for the diagnosis of endocarditis.125 The proximity to abdominal organs and major vessels, along with the absence of gastrointestinal air artifacts, is the advantage of TGAUS. However, a larger number of abdominal organs can be interrogated using transabdominal ultrasound compared to TGAUS.

In regard to Doppler studies comparing TGAUS and transabdominal ultrasound, hepatic vein examination with TGAUS was first described by Pinto et al,104 who showed it to be superior to a transabdominal approach.102,104 The success rate of TGAUS was 100% compared to 48% with a transabdominal approach. Examinations were not done simultaneously, but flow pattern and velocities were similar.104 Similar findings were recorded by another group, with the exception that Doppler tracings of the left hepatic vein could only be acquired in 18% of patients with TGAUS compared to 47% with transabdominal ultrasound. Hulin et al24 reported blunted hepatic venous flow in a patient after heart transplantation using both modalities simultaneously. RRI was measured with both TGAUS and transabdominal ultrasound in 2 studies of postoperative cardiac surgical patients.88,89 In the first study by Kararmaz et al,88 there was a statistically significant correlation between RRI done with TGAUS and RRI obtained using transabdominal ultrasound (r = 0.86, P < .0001). In the second study by Regolisti et al,89 both techniques were done sequentially and not compared. However, as observed in the first study, Regolisti et al89 observed that an elevated RRI was associated with an increased risk of postoperative renal failure but with a limited predictive ability. In terms of TGAUS of the stomach, gastric volume estimated with ultrasound was originally validated and compared to upper endoscopic examination findings. No comparison between TGAUS and surface ultrasound has been reported to this day. Doppler signals of the celiac artery, SMA, hepatic artery, splenic artery, and portal and splenic veins using both TGAUS and transabdominal ultrasound acquired simultaneously have also not been reported. However, portal pulsatility diagnosed with either method correlates with echocardiographic and hemodynamic parameters of right ventricular function75 and is associated with similar prolonged postoperative length of ICU stay.75,111,112 In addition, splenic venous Doppler signals have been correlated with the parameters of right ventricular function using TGAUS (Supplemental Digital Content 54, Figure 17, Video View 10, https://links.lww.com/AA/D521), similar to those reported using transabdominal ultrasound.103

Few studies have compared TGAUS with computed tomography or magnetic resonance. The spatial resolution of TGAUS remains higher than computed tomography.126 However, computed tomography provides more complete information on several organs inaccessible to TGAUS. Several studies have reported findings using both techniques. Moreover, TGAUS enables direct intraabdominal access views during the simultaneous performance of TEE and may uncover unrelated yet significant findings. TGAUS may provide a significant advantage over computed tomography or magnetic resonance imaging when a patient is critically ill, hemodynamically unstable, or already undergoing a surgical procedure.13

In one study, TGAUS and computed tomography of the descending aorta were performed to identify the position of the celiac artery.11 There was no significant difference between both methods. Another study described detecting an aortic dissection at the level of the mesenteric artery with visualization of the true and false lumens and the celiac trunk using TGAUS and computed tomography.13 The corresponding computed tomography examinations of TGAUS views 1, 4, and 8 are shown in Figure 3 (Supplemental Digital Content 4, Video View 1, https://links.lww.com/AA/D471) and Supplemental Digital Contents 23 and 44, Figures 7D and 14C, https://links.lww.com/AA/D490, https://links.lww.com/AA/D511. In a systematic review, the use of endoscopic ultrasound of the stomach for cancer staging was compared with computed tomography.127 In studies comparing them directly, endoscopic ultrasound performed better. Some trials have reported the diagnosis of renal cell tumor extension in the IVC diagnosed by TGAUS, computed tomography, and magnetic resonance imaging.50,52,53 In another study, computed tomography and TGAUS have been used in a patient with liver angioma undergoing liver resection,80 as well as in the diagnosis of portal air embolism (Supplemental Digital Contents 36 and 37, Figure 12, Video View 5, https://links.lww.com/AA/D503, https://links.lww.com/AA/D504),20 in splenic hematoma,81 and in renal cell carcinoma (Supplemental Digital Content 44, Figure 14F, https://links.lww.com/AA/D511). Dynamic Doppler changes during a medical78 or surgical intervention such as cavoatrial thrombectomy46,49,69,72 are radiation-free and easier to monitor with TGAUS than with computed tomography.

CONTRAINDICATIONS, COMPLICATIONS, FUTURE DEVELOPMENTS, AND LIMITATIONS OF TGAUS

The contraindications for TGAUS are similar to those for TEE128 and include absolute contraindications, such as esophageal stricture or tumor, and those that are relative, such as esophageal varices or a previous gastrointestinal surgery.128 Complications can arise from the use of both TEE and TGAUS. Oropharyngeal, esophageal, stomach, and splenic lacerations can be associated with the use of TEE and TGAUS.129–133 The invasive nature of the modality also precludes imaging in patients with known esophageal or gastric pathologies. In a survey that included 100,604 TGAUS procedures performed in 67 centers in Germany, the complication rate was 0.34%, and almost all complications were duodenal and esophageal perforations, with only 1 case of stomach perforation.134 The reduced risk of stomach perforation could be related to the increased flexibility of the stomach compared to the esophagus and the duodenum.135 As TGAUS does not allow imaging at the level of the duodenum, the risk is most likely similar to that associated with TEE. The risk of major complications mentioned to patients by gastroenterologists is <1 of 1000, a rate similar to that reported for TEE by Piercy et al.136 Comprehensive training and competency in the use of TEE remain essential elements to prevent such complications.8

The role of TGAUS in the imaging of other abdominal structures will likely continue to evolve. The relevance of TGAUS in exploring the anatomy of the small and large bowels and adrenal gland has been reported137–139 and should be studied with TGAUS in the perioperative setting and in the ICU. For perioperative applications, TGAUS is relegated to patients whose clinical conditions limit appropriate transabdominal ultrasound imaging. Common examples in the OR and ICU include patients presenting with morbid obesity, subcutaneous emphysema, anasarca, surgical dressings, and open chests or abdomens. In the OR, TEE and TGAUS provide the anesthesiologist with the ability to perform clinically useful noncardiac imaging that the surgical field and drapes would normally preclude. TGAUS is most useful when there is a cardiac indication for TEE probe placement, and an abdominal organ assessment is complementary.

As the resolution of ultrasound equipment such as 3D TGAUS will continue to evolve, the TEE and TGAUS probes of the future may allow improved imaging of structures outside of traditional cardiac applications. However, the anatomical location of the esophagus and stomach in relation to other structures will always be a major limiting factor. Finally, this review is based on the currently limited literature (Supplemental Digital Content 2, Table, https://links.lww.com/AA/D469), which only counts a few prospective and clinical trials, and on the authors’ bias and experience on the use of TGAUS. The proposed 10 views need to be systematically studied, compared, and validated with other modalities to determine their feasibility and usefulness. Outcome from a systematic use of TGAUS remains to be documented.

DISCLOSURES

Name: André Y. Denault, MD, PhD, ABIM-CCM, FRCPC, FASE, FCCS.

Contribution: This author helped with the conception and design; the acquisition, analysis, and interpretation of data; and critical revision for key intellectual content, gave final approval of the version to be published, and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: A. Y. Denault is on the Speakers Bureau for CAE Healthcare (2011), Masimo (2017), and Edwards (2019). He received a research grant from Edwards (2019).

Name: Michael Roberts, DO, FASE.

Contribution: This author helped acquire, analyze, and interpret the data and critically revise the key intellectual content; gave final approval of the version to be published; and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: None.

Name: Theodore Cios, MD, MPH, FASE.

Contribution: This author helped acquire, analyze, and interpret the data and critically revise the key intellectual content; gave final approval of the version to be published; and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: None.

Name: Anita Malhotra, MD.

Contribution: This author helped acquire, analyze, and interpret the data and critically revise the key intellectual content; gave final approval of the version to be published; and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: None.

Name: Sarto C. Paquin, MD.

Contribution: This author helped acquire, analyze, and interpret the data and critically revise the key intellectual content; gave final approval of the version to be published; and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: None.

Name: Stéphanie Tan, MD.

Contribution: This author helped acquire, analyze, and interpret the data and critically revise the key intellectual content; gave final approval of the version to be published; and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: None.

Name: Yiorgos Alexandros Cavayas, MD, MSc, FRCPC.

Contribution: This author helped acquire, analyze, and interpret the data and critically revise the key intellectual content; gave final approval of the version to be published; and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: None.

Name: Georges Desjardins, MD, FRCPC, FASE.

Contribution: This author helped with the conception and design; the acquisition, analysis, and interpretation of data for the work; and revising it critically for important intellectual content, gave final approval of the version to be published, and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: None.

Name: John Klick, MD, FCCP, FASE, FCCM.

Contribution: This author helped with the conception and design; the acquisition, analysis, and interpretation of data; and critical revision for key intellectual content, gave final approval of the version to be published, and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Conflicts of Interest: None.

This manuscript was handled by: Nikolaos J. Skubas, MD, DSc, FACC, FASE.

REFERENCES

1. Bryson GL, Grocott HP. Point-of-care ultrasound: a protean opportunity for perioperative care. Can J Anaesth. 2018;65:341–344.
2. Ramsingh D, Bronshteyn YS, Haskins S, Zimmerman J. Perioperative point-of-care ultrasound: from concept to application. Anesthesiology. 2020;132:908–916.
3. Chouinard MD, Pinheiro L, Nanda NC, Sanyal RS. Transgastric ultrasonography: a new approach for imaging the abdominal structures and vessels. Echocardiography. 1991;8:397–403.
4. Strohm WD, Phillip J, Hagenmüller F, Classen M. Ultrasonic tomography by means of an ultrasonic fiberendoscope. Endoscopy. 1980;12:241–244.
5. DiMagno EP, Buxton JL, Regan PT, et al. Ultrasonic endoscope. Lancet. 1980;1:629–631.
6. Bhutani MS, Deutsch JC. Digital Human Anatomy and Endoscopic Ultrasonography. 2005.B C Decker;
7. Hawes RH, Fockens P, Varadarajulu S. Endosonography. 2015.Saunders/Elsevier;
8. Hahn RT, Abraham T, Adams MS, et al.; American Society of Echocardiography; Society of Cardiovascular Anesthesiologists. Guidelines for performing a comprehensive transesophageal echocardiographic examination: recommendations from the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists. Anesth Analg. 2014;118:21–68.
9. Nicoara A, Skubas N, Ad N, et al. Guidelines for the use of transesophageal echocardiography to assist with surgical decision-making in the operating room: a surgery-based approach: from the American Society of Echocardiography in collaboration with the Society of Cardiovascular Anesthesiologists and the Society of Thoracic Surgeons. J Am Soc Echocardiogr. 2020;33:692–734.
10. Zhou L, Jariwala N, Frazin L. Should the celiac artery be used as an anatomical marker for the descending thoracic aorta during transesophageal echocardiography? Echocardiography. 2016;33:66–68.
11. Vasaiwala S, Vidovich MI, Connolly J, Frazin L. Transesophageal echocardiography of the descending thoracic aorta: establishing an accurate anatomic marker using the celiac artery. Echocardiography. 2010;27:1093–1097.
12. Orihashi K, Matsuura Y, Sueda T, et al. Abdominal aorta and visceral arteries visualized by transgastric echocardiography: technical considerations. Hiroshima J Med Sci. 1997;46:151–157.
13. Orihashi K, Sueda T, Okada K, Imai K. Perioperative diagnosis of mesenteric ischemia in acute aortic dissection by transesophageal echocardiography. Eur J Cardiothorac Surg. 2005;28:871–876.
14. Denault A, Liberman M, Paquin S. Extra-Cardiac Transesophageal Ultrasonography Basic Transesophageal and Critical Care Ultrasound. 2018:Taylor and Francis, CRC Press, 41–61.
15. Orihashi K, Matsuura Y, Sueda T, et al. Abdominal aorta and visceral arteries visualized with transesophageal echocardiography during operations on the aorta. J Thorac Cardiovasc Surg. 1998;115:945–947.
16. Orihashi K, Matsuura Y, Sueda T, Watari M, Okada K. Reversible visceral ischemia detected by transesophageal echocardiography and near-infrared spectroscopy. J Thorac Cardiovasc Surg. 2000;119:384–386.
17. Denault AY, Couture P, Vegas A, Buithieu J, Tardif JC. Transesophageal Echocardiography Multimedia Manual: A Perioperative Transdisciplinary Approach. 2011.2nd ed. Informa Healthcare;
    18. Biri S, Biri İ, Gultekin Y, Yurdakul M, Ozdemir M, Tola M. Doppler ultrasonography criteria of superior mesenteric artery stenosis. J Clin Ultrasound. 2019;47:267–271.
    19. Reed NR, Kalra M, Bower TC, Vrtiska TJ, Ricotta JJ II, Gloviczki P. Left renal vein transposition for nutcracker syndrome. J Vasc Surg. 2009;49:386–393.
    20. Denault A, Shaaban Ali M, Couture EJ, et al. A practical approach to cerebro-somatic near-infrared spectroscopy and whole-body ultrasound. J Cardiothorac Vasc Anesth. 2019;33(suppl 1):S11–S37.
    21. Denault A, Deschamps A, Murkin JM. A proposed algorithm for the intraoperative use of cerebral near-infrared spectroscopy. Semin Cardiothorac Vasc Anesth. 2007;11:274–281.
    22. Gårdebäck M, Settergren G, Brodin LA. Hepatic blood flow and right ventricular function during cardiac surgery assessed by transesophageal echocardiography. J Cardiothorac Vasc Anesth. 1996;10:318–322.
    23. Raymond M, Grønlykke L, Couture EJ, et al. Perioperative right ventricular pressure monitoring in cardiac surgery. J Cardiothorac Vasc Anesth. 2019;33:1090–1104.
    24. Hulin J, Aslanian P, Desjardins G, Belaïdi M, Denault A. The critical importance of hepatic venous blood flow Doppler assessment for patients in shock. A A Case Rep. 2016;6:114–120.
    25. Nomura T, Lebowitz L, Koide Y, Keehn L, Oka Y. Evaluation of hepatic venous flow using transesophageal echocardiography in coronary artery bypass surgery: an index of right ventricular function. J Cardiothorac Vasc Anesth. 1995;9:9–17.
    26. Denault AY, Couture P, Buithieu J, et al. Left and right ventricular diastolic dysfunction as predictors of difficult separation from cardiopulmonary bypass. Can J Anaesth. 2006;53:1020–1029.
    27. Couture P, Denault AY, Pellerin M, Tardif JC. Milrinone enhances systolic, but not diastolic function during coronary artery bypass grafting surgery. Can J Anaesth. 2007;54:509–522.
    28. Couture P, Denault AY, Shi Y, et al. Effects of anesthetic induction in patients with diastolic dysfunction. Can J Anaesth. 2009;56:357–365.
    29. Rudski LG, Lai WW, Afilalo J, et al. Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography. J Am Soc Echocardiogr. 2010;23:685–713.
    30. Denault AY, Beaulieu Y, Couture P, et al. Acute intraoperative effect of intravenous amiodarone on right ventricular function in patients undergoing valvular surgery. Eur Heart J Acute Cardiovasc Care. 2015;4:316–325.
    31. Fadel BM, Husain A, Alassoussi N, Dahdouh Z, Mohty D. Spectral Doppler of the hepatic veins in pulmonary hypertension. Echocardiography. 2015;32:170–173.
    32. Sun DD, Hou CJ, Yuan LJ, Duan YY, Hou Y, Zhou FP. Hemodynamic changes of the middle hepatic vein in patients with pulmonary hypertension using echocardiography. PLoS One. 2015;10:e0121408.
    33. Hekimsoy İ, Kibar Öztürk B, Soner Kemal H, et al. Hepatic and splenic sonographic and sonoelastographic findings in pulmonary arterial hypertension. Ultrasonography. 2021;40:281–288.
    34. Vegas A, Denault A, Royse C. A bedside clinical and ultrasound-based approach to hemodynamic instability—part II: bedside ultrasound in hemodynamic shock: continuing professional development. Can J Anaesth. 2014;61:1008–1027.
    35. Beaubien-Souligny W, Pépin MN, Legault L, et al. Acute kidney injury due to inferior vena cava stenosis after liver transplantation: a case report about the importance of hepatic vein Doppler ultrasound and clinical assessment. Can J Kidney Health Dis. 2018;5:2054358118801012.
    36. Jacobsohn E, Avidan MS, Hantler CB, Rosemeier F, De Wet CJ. Case report: inferior vena-cava right atrial anastomotic stenosis after bicaval orthotopic heart transplantation. Can J Anaesth. 2006;53:1039–1043.
    37. Bjerke RJ, Mieles LA, Borsky BJ, Todo S. The use of transesophageal ultrasonography for the diagnosis of inferior vena caval outflow obstruction during liver transplantation. Transplantation. 1992;54:939–941.
    38. Ko EY, Kim TK, Kim PN, Kim AY, Ha HK, Lee MG. Hepatic vein stenosis after living donor liver transplantation: evaluation with Doppler US. Radiology. 2003;229:806–810.
    39. Almeida J, Garcia R, Monteiro V, Pinho P. Pseudo-pericardial tamponade after cardiac surgery. J Am Soc Echocardiogr. 2009;22:211.e5–211.e6.
    40. Mizuguchi KA, Padera RF Jr, Kowalczyk A, Doran MN, Couper GS, Fox AA. Transesophageal echocardiography imaging of the total artificial heart. Anesth Analg. 2013;117:780–784.
    41. Rehfeldt KH, Wittwer ED, Mauermann WJ. Inferior vena cava obstruction after total artificial heart implantation. Anesth Analg. 2014;119:26–29.
    42. Essandoh M, Whitson BA. Caval stenosis after bicaval orthotopic heart transplantation: routine transesophageal echocardiography assessment of the caval anastomoses may avert this complication. J Cardiothorac Vasc Anesth. 2020;34:568–569.
    43. Blinn JA, Margulis V, Joshi RV. Transesophageal echocardiography imaging of the inferior vena cava and hepatic vein masses. A A Pract. 2019;12:295–297.
    44. Huang J, Zhou J, Settles D, Maher T. Evaluation of hepatic structures by transesophageal echocardiography. J Cardiothorac Vasc Anesth. 2014;28:1328–1330.
    45. Schallner N, Wittau N, Kehm V, Humburger F, Schmidt R, Steinmann D. Intraoperative pulmonary tumor embolism from renal cell carcinoma and a patent foramen ovale detected by transesophageal echocardiography. J Cardiothorac Vasc Anesth. 2011;25:145–147.
    46. Sobczyński R, Golabek T, Mazur P, Chłosta P. Transoesophageal echocardiography reduces invasiveness of cavoatrial tumour thrombectomy. Wideochir Inne Tech Maloinwazyjne. 2014;9:479–483.
    47. Burbano NH, Vlah C, Argalious M. Residual inferior vena cava thrombus detected by transesophageal echocardiography after resection of a malignant adrenal mass. A A Case Rep. 2015;5:143–145.
    48. El-Sayed Ahmed MM, Al-Najjar RM, Aftab M, Anton JM, Colen JS, Reul RM. Early detection of a cavopulmonary tumor embolus with the use of transesophageal echocardiography. Tex Heart Inst J. 2015;42:66–69.
    49. Seiler A, Gnadinger P, Glotzbach J, Silverton NA. Transesophageal echocardiography-guided tumor/thrombus debulking using the angiovac transcatheter aspiration device. J Cardiothorac Vasc Anesth. 2020;34:1005–1009.
    50. Oikawa T, Shimazui T, Johraku A, et al. Intraoperative transesophageal echocardiography for inferior vena caval tumor thrombus in renal cell carcinoma. Int J Urol. 2004;11:189–192.
    51. Komanapalli CB, Tripathy U, Sokoloff M, Daneshmand S, Das A, Slater MS. Intraoperative renal cell carcinoma tumor embolization to the right atrium: incidental diagnosis by transesophageal echocardiography. Anesth Analg. 2006;102:378–379.
    52. Treiger BF, Humphrey LS, Peterson CV Jr, et al. Transesophageal echocardiography in renal cell carcinoma: an accurate diagnostic technique for intracaval neoplastic extension. J Urol. 1991;145:1138–1140.
    53. Sigman DB, Hasnain JU, Del Pizzo JJ, Sklar GN. Real-time transesophageal echocardiography for intraoperative surveillance of patients with renal cell carcinoma and vena caval extension undergoing radical nephrectomy. J Urol. 1999;161:36–38.
    54. Allen G, Klingman R, Ferraris VA, Fisher H, Harte F, Singh A. Transesophageal echocardiography in the surgical management of renal cell carcinoma with intracardiac extension. J Cardiovasc Surg (Torino). 1991;32:833–836.
    55. Singh I, Jacobs LE, Kotler MN, Ioli A. The utility of transesophageal echocardiography in the management of renal cell carcinoma with intracardiac extension. J Am Soc Echocardiogr. 1995;8:245–250.
    56. Chen H, Ng V, Kane CJ, Russell IA. The role of transesophageal echocardiography in rapid diagnosis and treatment of migratory tumor embolus. Anesth Analg. 2004;99:357–359.
    57. Hou JZ, Zeng ZC, Wang BL, Yang P, Zhang JY, Mo HF. High dose radiotherapy with image-guided hypo-IMRT for hepatocellular carcinoma with portal vein and/or inferior vena cava tumor thrombi is more feasible and efficacious than conventional 3D-CRT. Jpn J Clin Oncol. 2016;46:357–362.
    58. Berman AT, Parmet JL, Harding SP, et al. Emboli observed with use of transesophageal echocardiography immediately after tourniquet release during total knee arthroplasty with cement. J Bone Joint Surg Am. 1998;80:389–396.
    59. Hudcova J, Schumann R. Fatal right ventricular failure with intracardiac thrombus formation during liver transplantation not apparent on postmortem examination. Anesth Analg. 2006;103:506.
    60. Tashjian JA, Fraint H, DiNardo J, Rouine-Rapp K. Inferior vena cava thrombus in a postpartum patient with Fontan physiology: a case report. A A Case Rep. 2017;9:136–139.
    61. Nanji JA, Ansari JR, Yurashevich M, et al. Transesophageal echocardiographic observation of caval thrombus followed by intraoperative placement of inferior vena cava filter for presumed pulmonary embolism during cesarean hysterectomy for placenta percreta: a case report. A A Pract. 2019;12:37–40.
    62. Vetrugno L, Barbariol F, Baccarani U, Forfori F, Volpicelli G, Della Rocca G. Transesophageal echocardiography in orthotopic liver transplantation: a comprehensive intraoperative monitoring tool. Crit Ultrasound J. 2017;9:15.
    63. Diebel LN, Wilson RF, Dulchavsky SA, Saxe J. Effect of increased intra-abdominal pressure on hepatic arterial, portal venous, and hepatic microcirculatory blood flow. J Trauma. 1992;33:279–282.
    64. Casanova GA, Zingg EJ. Inferior vena caval tumor extension in renal cell carcinoma. Urol Int. 1991;47:216–218.
    65. Skinner DG, Pritchett TR, Lieskovsky G, Boyd SD, Stiles QR. Vena caval involvement by renal cell carcinoma. Surgical resection provides meaningful long-term survival. Ann Surg. 1989;210:387–392.
    66. George J, Grebenik K, Patel N, Cranston D, Westaby S. The importance of intraoperative transoesophageal monitoring when operating on renal cancers that involve the right atrium. Ann R Coll Surg Engl. 2014;96:e18–e19.
    67. Thangaswamy CR, Manikandan R, Bathala Vedagiri SC. Role of transoesophageal echocardiography in renal cell carcinoma: a brief review. BMJ Case Reports. 2017;2017:bcr2017221532.
    68. Calderone CE, Tuck BC, Gray SH, Porter KK, Rais-Bahrami S. The role of transesophageal echocardiography in the management of renal cell carcinoma with venous tumor thrombus. Echocardiography. 2018;35:2047–2055.
    69. Souki FG, Demos M, Fermin L, Ciancio G. Transesophageal echocardiography-guided thrombectomy of intracardiac renal cell carcinoma without cardiopulmonary bypass. Ann Card Anaesth. 2016;19:740–743.
    70. Essandoh M, Tang J, Essandoh G, et al. Transesophageal echocardiography guidance for robot-assisted level III inferior vena cava tumor thrombectomy: a novel approach to intraoperative care. J Cardiothorac Vasc Anesth. 2018;32:2623–2627.
    71. Kostibas MP, Arora V, Gorin MA, et al. Defining the role of intraoperative transesophageal echocardiography during radical nephrectomy with inferior vena cava tumor thrombectomy for renal cell carcinoma. Urology. 2017;107:161–165.
    72. Zlatanovic P, Koncar I, Jakovljevic N, Markovic D, Mitrovic A, Davidovic L. Transesophageal echocardiography-guided thrombectomy of level IV renal cell carcinoma without cardiopulmonary bypass. Braz J Cardiovasc Surg. 2019;34:229–232.
    73. Martinelli SM, Mitchell JD, McCann RL, Podgoreanu MV, Mathew JP, Swaminathan M. Intraoperative transesophageal echocardiography diagnosis of residual tumor fragment after surgical removal of renal cell carcinoma. Anesth Analg. 2008;106:1633–1635.
    74. Sharma V, Cusimano RJ, McNama P, Wasowicz M, Ko R, Meineri M. Intraoperative migration of an inferior vena cava tumour detected by transesophageal echocardiography. Can J Anaesth. 2011;58:468–470.
    75. Eljaiek R, Cavayas YA, Rodrigue E, et al. High postoperative portal venous flow pulsatility indicates right ventricular dysfunction and predicts complications in cardiac surgery patients. Br J Anaesth. 2019;122:206–214.
    76. Denault AY, Beaubien-Souligny W, Elmi-Sarabi M, et al. Clinical significance of portal hypertension diagnosed with bedside ultrasound after cardiac surgery. Anesth Analg. 2017;124:1109–1115.
    77. Beaubien-Souligny W, Denault A, Robillard P, Desjardins G. The role of point-of-care ultrasound monitoring in cardiac surgical patients with acute kidney injury. J Cardiothorac Vasc Anesth. 2019;33:2781–2796.
    78. Beaubien-Souligny W, Denault AY. Real-time assessment of renal venous flow by transesophageal echography during cardiac surgery. A A Pract. 2019;12:30–32.
    79. Vannucci A, Johnston J, Earl TM, Doyle M, Kangrga IM. Intraoperative transesophageal echocardiography guides liver transplant surgery in a patient with thrombosed transjugular intrahepatic portosystemic shunt. Anesthesiology. 2011;115:1389–1391.
    80. Vetrugno L, Pompei L, Zearo E, Della Rocca G. Could transesophageal echocardiography be useful in selected cases during liver surgery resection? J Ultrasound. 2016;19:47–52.
    81. Poularas J, Saranteas T, Karakitsos D, Karabinis A. Transoesophageal ultrasound monitoring of subcapsular splenic haematoma in the intensive care unit. Anaesth Intensive Care. 2009;37:862–863.
    82. Royse CF, Bird H, Royse AG. Routine assessment of coeliac axis and renal artery flow is not feasible with transoesophageal echocardiography. Anaesthesia. 2009;64:103–104.
    83. Yang PL, Wong DT, Dai SB, et al. The feasibility of measuring renal blood flow using transesophageal echocardiography in patients undergoing cardiac surgery. Anesth Analg. 2009;108:1418–1424.
    84. Bandyopadhyay S, Kumar Das R, Paul A, Sundar Bhunia K, Roy D. A transesophageal echocardiography technique to locate the kidney and monitor renal perfusion. Anesth Analg. 2013;116:549–554.
    85. Garwood S, Davis E, Harris SN. Intraoperative transesophageal ultrasonography can measure renal blood flow. J Cardiothorac Vasc Anesth. 2001;15:65–71.
    86. Zabala L, Ullah S, Pierce CD, et al. Transesophageal Doppler measurement of renal arterial blood flow velocities and indices in children. Anesth Analg. 2012;114:1277–1284.
    87. Andrew BY, Cherry AD, Hauck JN, et al. The association of aortic valve pathology with renal resistive index as a kidney injury biomarker. Ann Thorac Surg. 2018;106:107–114.
    88. Kararmaz A, Kemal Arslantas M, Cinel I. Renal resistive index measurement by transesophageal echocardiography: comparison with translumbar ultrasonography and relation to acute kidney injury. J Cardiothorac Vasc Anesth. 2015;29:875–880.
    89. Regolisti G, Maggiore U, Cademartiri C, et al. Renal resistive index by transesophageal and transparietal echo-Doppler imaging for the prediction of acute kidney injury in patients undergoing major heart surgery. J Nephrol. 2017;30:243–253.
    90. Andrew BY, Andrew EY, Cherry AD, et al. Intraoperative renal resistive index as an acute kidney injury biomarker: development and validation of an automated analysis algorithm. J Cardiothorac Vasc Anesth. 2018;32:2203–2209.
    91. Pellerito J, Polak J. Introduction to Vascular Ultrasonography. 2012.6th ed. Elsevier Health Sciences;
    92. Asbeutah AM, Buredha B, Mahmood M, Al-Mohana A. Doppler waveform characteristics in the celiac and superior mesenteric arteries in normal children and adults with the use of duplex ultrasound. J Vasc Ultrasound. 2018;32:133–136.
    93. Wood MM, Romine LE, Lee YK, et al. Spectral Doppler signature waveforms in ultrasonography: a review of normal and abnormal waveforms. Ultrasound Q. 2010;26:83–99.
    94. Myers KA, Clough A. Making Sense of Vascular Ultrasound: A Hands-on Guide. 2004.Arnold;
      95. Brusasco C, Tavazzi G, Robba C, et al. Splenic Doppler resistive index variation mirrors cardiac responsiveness and systemic hemodynamics upon fluid challenge resuscitation in postoperative mechanically ventilated patients. Biomed Res Int. 2018;2018:1978968.
      96. Sakamoto T, Fujiogi M, Matsui H, Fushimi K, Yasunaga H. Clinical features and outcomes of nonocclusive mesenteric ischemia after cardiac surgery: a retrospective cohort study. Heart Vessels. 2020;35:630–636.
      97. Siddiqui WJ, Bakar A, Aslam M, et al. Left renal vein compression syndrome: cracking the nut of clinical dilemmas—three cases and review of literature. Am J Case Rep. 2017;18:754–759.
      98. Perlas A, Mitsakakis N, Liu L, et al. Validation of a mathematical model for ultrasound assessment of gastric volume by gastroscopic examination. Anesth Analg. 2013;116:357–363.
      99. Ikeda Y, Ishii S, Yazaki M, et al. Portal congestion and intestinal edema in hospitalized patients with heart failure. Heart Vessels. 2018;33:740–751.
      100. Perlas A, Chan VW, Lupu CM, Mitsakakis N, Hanbidge A. Ultrasound assessment of gastric content and volume. Anesthesiology. 2009;111:82–89.
      101. Sato K, Kawamura T, Wakusawa R. Hepatic blood flow and function in elderly patients undergoing laparoscopic cholecystectomy. Anesth Analg. 2000;90:1198–1202.
      102. Meierhenric R, Gauss A, Georgieff M, Schütz W. Use of multi-plane transoesophageal echocardiography in visualization of the main hepatic veins and acquisition of Doppler sonography curves. Comparison with the transabdominal approach. Br J Anaesth. 2001;87:711–717.
      103. Bolognesi M, Quaglio C, Bombonato G, et al. Splenic Doppler impedance indices estimate splenic congestion in patients with right-sided or congestive heart failure. Ultrasound Med Biol. 2012;38:21–27.
      104. Pinto FJ, Wranne B, St Goar FG, Schnittger I, Popp RL. Hepatic venous flow assessed by transesophageal echocardiography. J Am Coll Cardiol. 1991;17:1493–1498.
      105. Menaker J, Tabatabai A, Rector R, et al. Incidence of cannula-associated deep vein thrombosis after veno-venous extracorporeal membrane oxygenation. ASAIO J. 2017;63:588–591.
      106. Chartier L, Béra J, Delomez M, et al. Free-floating thrombi in the right heart: diagnosis, management, and prognostic indexes in 38 consecutive patients. Circulation. 1999;99:2779–2783.
      107. Schütz W, Meierhenrich R, Träger K, Gauss A, Radermacher P, Georgieff M. Is it feasible to monitor total hepatic blood flow by use of transesophageal echography? An experimental study in pigs. Intensive Care Med. 2001;27:580–585.
      108. Denault A, Vegas A, Lamarche Y, Tardif J, Couture P. Basic Transesophageal and Critical Care Ultrasound. 2018.Taylor and Francis, CRC Press;
      109. Kok T, van der Jagt EJ, Haagsma EB, Bijleveld CM, Jansen PL, Boeve WJ. The value of Doppler ultrasound in cirrhosis and portal hypertension. Scand J Gastroenterol Suppl. 1999;230:82–88.
      110. Styczynski G, Milewska A, Marczewska M, et al. Echocardiographic correlates of abnormal liver tests in patients with exacerbation of chronic heart failure. J Am Soc Echocardiogr. 2016;29:132–139.
      111. Beaubien-Souligny W, Eljaiek R, Fortier A, et al. The association between pulsatile portal flow and acute kidney injury after cardiac surgery: a retrospective cohort study. J Cardiothorac Vasc Anesth. 2018;32:1780–1787.
      112. Beaubien-Souligny W, Benkreira A, Robillard P, et al. Alterations in portal vein flow and intrarenal venous flow are associated with acute kidney injury after cardiac surgery: a prospective observational cohort study. J Am Heart Assoc. 2018;7:e009961.
      113. García-Criado A, Gilabert R, Salmerón JM, et al. Significance of and contributing factors for a high resistive index on Doppler sonography of the hepatic artery immediately after surgery: prognostic implications for liver transplant recipients. AJR Am J Roentgenol. 2003;181:831–838.
      114. Stankovic Z, Csatari Z, Deibert P, et al. Normal and altered three-dimensional portal venous hemodynamics in patients with liver cirrhosis. Radiology. 2012;262:862–873.
      115. Beaubien-Souligny W, Huard G, Bouchard J, Lamarche Y, Denault A, Albert M. Doppler renal resistance index for the prediction of response to passive leg-raising following cardiac surgery. J Clin Ultrasound. 2018;46:455–460.
      116. Iida N, Seo Y, Sai S, et al. Clinical implications of intrarenal hemodynamic evaluation by Doppler ultrasonography in heart failure. JACC Heart Fail. 2016;4:674–682.
      117. Bossard G, Bourgoin P, Corbeau JJ, Huntzinger J, Beydon L. Early detection of postoperative acute kidney injury by Doppler renal resistive index in cardiac surgery with cardiopulmonary bypass. Br J Anaesth. 2011;107:891–898.
      118. Guinot PG, Bernard E, Abou Arab O, et al. Doppler-based renal resistive index can assess progression of acute kidney injury in patients undergoing cardiac surgery. J Cardiothorac Vasc Anesth. 2013;27:890–896.
      119. Hertzberg D, Ceder SL, Sartipy U, Lund K, Holzmann MJ. Preoperative renal resistive index predicts risk of acute kidney injury in patients undergoing cardiac surgery. J Cardiothorac Vasc Anesth. 2017;31:847–852.
      120. Husain-Syed F, Birk HW, Ronco C, et al. Doppler-derived renal venous stasis index in the prognosis of right heart failure. J Am Heart Assoc. 2019;8:e013584.
      121. Puzzovivo A, Monitillo F, Guida P, et al. Renal venous pattern: a new parameter for predicting prognosis in heart failure outpatients. J Cardiovasc Dev Dis. 2018;5:52.
      122. Hatcher PA, Anderson EE, Paulson DF, Carson CC, Robertson JE. Surgical management and prognosis of renal cell carcinoma invading the vena cava. J Urol. 1991;145:20–23.
      123. Neves RJ, Zincke H. Surgical treatment of renal cancer with vena cava extension. Br J Urol. 1987;59:390–395.
      124. Clarke R, Wells J, Finn C. Morphology identification using transesophageal echocardiography in migratory renal cell carcinoma surgery. J Cardiothorac Vasc Anesth. 2011;25:153–155.
      125. Birmingham GD, Rahko PS, Ballantyne F III. Improved detection of infective endocarditis with transesophageal echocardiography. Am Heart J. 1992;123:774–781.
      126. Kim IC, Chang S, Hong GR, et al. Comparison of cardiac computed tomography with transesophageal echocardiography for identifying vegetation and intracardiac complications in patients with infective endocarditis in the era of 3-dimensional images. Circ Cardiovasc Imaging. 2018;11:e006986.
      127. Kelly S, Harris KM, Berry E, et al. A systematic review of the staging performance of endoscopic ultrasound in gastro-oesophageal carcinoma. Gut. 2001;49:534–539.
      128. Mayo PH, Narasimhan M, Koenig S. Critical care transesophageal echocardiography. Chest. 2015;148:1323–1332.
      129. Chow MS, Taylor MA, Hanson CW III. Splenic laceration associated with transesophageal echocardiography. J Cardiothorac Vasc Anesth. 1998;12:314–316.
      130. Olenchock SA Jr, Lukaszczyk JJ, Reed J III, Theman TE. Splenic injury after intraoperative transesophageal echocardiography. Ann Thorac Surg. 2001;72:2141–2143.
      131. Côté G, Denault A. Transesophageal echocardiography-related complications. Can J Anaesth. 2008;55:622–647.
      132. Hilberath JN, Oakes DA, Shernan SK, Bulwer BE, D’Ambra MN, Eltzschig HK. Safety of transesophageal echocardiography. J Am Soc Echocardiogr. 2010;23:1115–1127.
      133. Ramalingam G, Choi SW, Agarwal S, et al.; Association of Cardiothoracic Anaesthesia and Critical Care. Complications related to peri-operative transoesophageal echocardiography—a one-year prospective national audit by the Association of Cardiothoracic Anaesthesia and Critical Care. Anaesthesia. 2020;75:21–26.
      134. Jenssen C, Faiss S, Nürnberg D. [Complications of endoscopic ultrasound and endoscopic ultrasound-guided interventions—results of a survey among German centers]. Z Gastroenterol. 2008;46:1177–1184.
      135. Jenssen C, Alvarez-Sánchez MV, Napoléon B, Faiss S. Diagnostic endoscopic ultrasonography: assessment of safety and prevention of complications. World J Gastroenterol. 2012;18:4659–4676.
      136. Piercy M, McNicol L, Dinh DT, Story DA, Smith JA. Major complications related to the use of transesophageal echocardiography in cardiac surgery. J Cardiothorac Vasc Anesth. 2009;23:62–65.
      137. Sandek A, Bauditz J, Swidsinski A, et al. Altered intestinal function in patients with chronic heart failure. J Am Coll Cardiol. 2007;50:1561–1569.
      138. Maturen KE, Wasnik AP, Kamaya A, et al. Ultrasound imaging of bowel pathology: technique and keys to diagnosis in the acute abdomen. AJR Am J Roentgenol. 2011;197:W1067–W1075.
      139. Gottlieb M, Peksa GD, Pandurangadu AV, Nakitende D, Takhar S, Seethala RR. Utilization of ultrasound for the evaluation of small bowel obstruction: a systematic review and meta-analysis. Am J Emerg Med. 2018;36:234–242.

      Supplemental Digital Content

      Copyright © 2021 International Anesthesia Research Society