Secondary Logo

Journal Logo

A Transesophageal Echocardiography Technique to Locate the Kidney and Monitor Renal Perfusion

Bandyopadhyay, Saikat, MBBS, DA, MD, FCCM; Kumar Das, Ratan, MBBS, MS, MCh; Paul, Abhijit, MBBS, DA, MD; Sundar Bhunia, Kalyan, MBBS, DNB; Roy, Deeptarka, MBBS, MD

doi: 10.1213/ANE.0b013e31827ab3b1
Cardiovascular Anesthesiology: Technical Communication
Free

Monitoring the renal arterial Doppler flow velocity indices, the resistive index and pulsatility index, with ultrasound may help predict renal dysfunction. However, such monitoring has been done intermittently by transcutaneous ultrasound in the postoperative intensive care setting. In the operating room, transesophageal echocardiography (TEE) is an alternative to transcutaneous ultrasound for obtaining indices of renal perfusion. However, it is difficult to locate the right kidney using TEE. We propose a new technique to locate the left kidney that, in our experience, is simple and easy to perform. We believe, starting from a transgastric left ventricular short-axis view, turning left to locate the abdominal aorta, and following it to the origin of the left renal artery may help locate the left kidney faster than previously described techniques. We also propose a new technique to monitor these Doppler indices using TEE during the intraoperative period.

From the Department of Anesthesiology and Pain Medicine, Department of Cardiothoracic and Vascular Surgery and the Department of Critical Care Medicine, Medica Superspecialty Hospital, Kolkata, India.

Accepted for publication October 8, 2012.

The authors declare no conflicts of interest.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.anesthesia-analgesia.org).

Reprints will not be available from the authors.

Address correspondence to Saikat Bandyopadhyay, MBBS, DA, MD, FCCM, D 401 Mayfair Greens, 449 S.N. Ghosh Ave., Narendrapur, Kolkata 700103, India. Address e-mail to drsakiban@gmail.com.

The search for clinical markers to detect and monitor acute kidney injury (AKI) as early as possible has been the focus of interest of investigators all around the world. The predictive value of serum creatinine, the most widely used variable to monitor renal function as an early marker of AKI, is rather poor.1

The ultrasound assessment of renal artery flow has been shown to be highly sensitive and specific in the early detection of AKI.2,3 On the basis of Doppler measurements of renal artery velocities, the resistive index (RI) is calculated as: RI = (peak systolic velocity – minimum diastolic velocity)/peak systolic velocity; and the pulsatility index (PI) is calculated as: PI = (peak systolic velocity – minimum diastolic velocity)/mean velocity.4

These indices are associated with resistance to flow distal to the point of measurement, with a higher value indicating increased resistance.2 However, they are affected by several interrelated variables (Table 1). The range of values of RI and PI in normal subjects is approximately 0.64 to 0.704,10 and 0.93 to 1.25,4 respectively. Bossard et al.3 recently reported that RI values >0.79 measured postoperatively in cardiac surgical patients predicted the onset of AKI, with values >0.83 predicting the need for dialysis. It may be worthwhile monitoring these indices in patients undergoing cardiopulmonary bypass having a higher risk of AKI (e.g., valvular surgery, prolonged bypass times, age >65 years)11 and those with preexisting comorbidities (e.g., decreased left ventricular ejection fraction, diabetes, borderline renal function).12

Table 1

Table 1

Most of the studies assessing these indices were done using transcutaneous ultrasound, which is not feasible to perform in the operating room. Transesophageal echocardiography (TEE) is an alternative.

We present a technique to image the left kidney and measure the RI and PI with TEE. As reported by Yang et al.,13 and consistent with our own experience, imaging of the right kidney is difficult because it lies too low inside the abdominal cavity, farther away from the esophagus. We therefore describe a technique to locate the left kidney.

Back to Top | Article Outline

METHODS

Sonography of the Left Kidney: How Does the Normal Kidney Look Using TEE?

It is essential for the inexperienced echocardiographer to be able to identify and differentiate the left kidney from closely related intra-abdominal organs. Figure 1 depicts the anatomical relationship between the left kidney and the related organs. Figure 2 demonstrates the transverse and longitudinal sonographic images of the left kidney in 2 dimensions and with color flow Doppler (CFD).

Figure 1

Figure 1

Figure 2

Figure 2

Back to Top | Article Outline

The Technique

We used a standard ultrasound machine (Philips HD 11 XE; Philips, Bothell, WA), a multiplane TEE probe, and a lower frequency (5 MHz) to better visualize the deeper intra-abdominal organs. Although the left kidney can be located, it may be impossible to obtain adequate images of the renal vasculature using standard cardiac presets. Therefore, a vascular preset becomes an essential prerequisite to ensure optimum visualization of the renal vasculature and allow for automated measurement of RI and PI.

The probe is advanced approximately 30 cm from the upper incisor teeth, and a standard midesophageal 4-chamber view is obtained. Starting from the 4-chamber view, the probe is advanced a further 8 to 10 cm to lead it through the short abdominal part of the esophagus eventually into the stomach and anteflexed to obtain a midpapillary transgastric short-axis (TG SAX) view. The esophagus lies initially along the right side of the descending aorta, then runs in front, and eventually a little left of the aorta. We believe that considerable ease in locating the left kidney occurs if the performer uses a simple maneuver we termed as the corkscrew technique (Fig. 3) (Video 1, see Supplemental Digital Content 1, http://links.lww.com/AA/A498) because of the TEE probe manipulations required to obtain the view. The direction of the turns of the probe to reach the left kidney follow a “corkscrew” pattern using the following steps:

Figure 3

Figure 3

Video 1

Video 1

  • STEP 1: Obtain a TG SAX view (Point A).
  • STEP 2: Turn the probe 90 to 270 degrees toward the LEFT until the SAX view of the descending aorta is imaged. The aorta is imaged anterior to the oval hypoechogenic vertebral body (Fig. 1)—(Point B).
  • STEP 3: Advance the probe (4–6 cm) following the aorta to the origin of the left renal artery (Point C). Use CFD to image the blood flow in left renal vessels.
  • STEP 4: Following the left renal artery, turn the probe RIGHT 90 degrees until the left kidney is visualized (Point D).

It is important to note that after an approximately 90- to 270-degree turn from TG SAX view, the transducer directly faces the aorta. Following it to the origin of the left renal artery, a turn of the probe to the right will help locate the left kidney. In cases where the origin of the left renal artery (from the aorta) cannot be located, a blind 90-degree right turn with probe advanced 4 to 6 cm beyond Point B may help locate the left kidney.

It is crucial to recognize the spleen and differentiate it from the left kidney. The concave inner border of the spleen comes in relation with the convex outer border of the left kidney. The spleen can be located by turning the probe farther to the right from the position where the SAX view of the left kidney is obtained. The spleen is uniformly hypoechogenic in contrast to the kidney, which has a central echogenic pelvis and hypoechogenic peripheral cortex, surrounded by the brightly echogenic fascia of Gerota and perinephric fat pad (Fig. 1B). In cases in which the echocardiographer experiences difficulty locating the spleen by merely turning the probe to the right, gently withdrawing the probe a few centimeters while turning it to the right may help locate the splenic vessels under CFD, which can be traced up to the splenic hilum to locate the concave inner border of the spleen.

The probe is finely adjusted until a clear image of the left kidney is obtained. CFD (Nyquist limit 15–20 cm/s) is used to visualize the renal vasculature. The kidney being one of the most vascular organs clearly stands out when CFD is used. Placing a CFD over the mid portion of the kidney body and varying the probe angle (0–30 degrees) may help visualize both the aorta and the left kidney simultaneously (Video 2, see Supplemental Digital Content 2, http://links.lww.com/AA/A499). Approximately 10% to 30% of individuals have multiple renal arteries (most common occurrence being another additional vessel) on each side.14 On reaching the hilum, the main renal artery divides into segmental branches that give rise to the interlobar arteries that divide again forming the arcuate arteries at the corticomedullary junction. The arcuate arteries traveling across the renal pyramids give rise to the interlobular arteries (Video 3, see Supplemental Digital Content 3, http://links.lww.com/AA/A500). With experience, one may be able to distinguish the branches from the main renal artery taking into consideration the relative size, order, and sequence of the branching. Once a clear view of the vessels is obtained, pulsed-wave Doppler is used to differentiate the main renal artery from the vein 1 to 2 cm before the hilum (Fig. 4).

Video 2

Video 2

Video 3

Video 3

Figure 4

Figure 4

The cursor is placed on the main renal artery (small gate, 1.2–1.8 mm is preferable) until a clear flow velocity waveform is obtained. When using the vascular preset, activation of the software will automatically trace the spectral Doppler envelopes (Video 4, see Supplemental Digital Content 4, http://links.lww.com/AA/A501) and calculate the Doppler indices RI and PI. In case the automated software is unavailable in the ultrasound platform, the indices may be able to be calculated after manually tracing the Doppler envelopes using the formulae mentioned previously following these steps (Fig. 5):

Figure 5

Figure 5

  • STEP 1: Obtain a good quality arterial Doppler flow velocity waveform and freeze it.
  • STEP 2: Use calipers to measure the peak systolic velocity (1.13 m/s) and the minimum diastolic velocity (0.250 m/s). Trace the waveform manually to obtain the mean velocity (0.402 m/s).

To obtain a mean value, the Doppler indices are measured over 3 to 5 cardiac cycles, and the average value is calculated. The TEE probe can be withdrawn to monitor the cardiac function and can be readvanced to locate the left kidney and renal artery at will. Because the corkscrew technique is simple, relocating the left kidney and continuing renal monitoring should not be difficult.

Back to Top | Article Outline

DISCUSSION

Although automated (or manual) calculation of the indices is possible, a few words of caution can help to obtain correct measurements and avoid unnecessary errors. It is mandatory to have a clear and continuous display of the velocity waveforms. Too much variability among individual waveforms (e.g., arrhythmias) can lead to error in calculation. Variability is more of an issue when relying on data generated by the automatic tracking system, whereas in the operator-selected waveforms it is up to the operator to choose comparable, similar waveforms. Data can be accepted as correct if the automated tracing of the waveform is perfectly aligned along its margin (Video 4, see Supplemental Digital Content 4, http://links.lww.com/AA/A501). The best way to obtain correct measurements is to ensure good quality waveform display by optimizing depth, adjusting gain, and placing the Doppler gate directly in the center of the renal artery. Although we record the Doppler indices from the main renal artery, these indices convey similar information when derived from branches of the renal artery.15 It is important to ensure that the measurements are taken from the renal and not from another artery, for example, splenic artery, which can be accomplished by tracing the renal artery from its origin to the hilum before taking Doppler measurements.

Video 4

Video 4

There are safety concerns over the prolonged use of Doppler ultrasound.16 We limit our use of automated monitoring to a few seconds at a time and routinely keep the power at its lowest limits without compromising on image quality. It is not possible to calculate total renal blood flow from a branch artery, but monitoring the Doppler indices may help to closely monitor renal perfusion.

Although the corkscrew technique helps to locate the left kidney with relative ease, locating the left renal artery can be a limiting factor because it may not always be possible to locate its origin from the aorta. Further studies are needed to evaluate the effectiveness of this technique in helping inexperienced echocardiographers locate the left kidney, to assess the intraoperative role of renal perfusion monitoring, and to investigate whether such monitoring has any clear advantage in predicting AKI at the earliest stage.

Back to Top | Article Outline

DISCLOSURES

Name: Saikat Bandyopadhyay, MBBS, DA, MD, FCCM.

Contribution: This author helped design and conduct the study, analyze the data, and prepare the manuscript.

Attestation: Saikat Bandyopadhyay attests to the integrity of the analysis and approved the final manuscript.

Name: Ratan Kumar Das, MBBS, MS, MCh.

Contribution: This author helped prepare the manuscript.

Attestation: Ratan Kumar Das attests to the integrity of the analysis and approved the final manuscript.

Name: Abhijit Paul, MBBS, DA, MD.

Contribution: This author helped prepare the manuscript.

Attestation: Abhijit Paul attests to the integrity of the analysis and approved the final manuscript.

Name: Kalyan Sundar Bhunia, MBBS, DNB.

Contribution: This author helped prepare the manuscript.

Attestation: Kalyan Sundar Bhunia attests to the integrity of the analysis and approved the final manuscript.

Name: Deeptarka Roy, MBBS, MD.

Contribution: This author helped prepare the manuscript.

Attestation: Deeptarka Roy attests to the integrity of the analysis and approved the final manuscript.

This manuscript was handled by: Martin J. London, MD.

Back to Top | Article Outline

REFERENCES

1. Herget-Rosenthal S, Marggraf G, Hüsing J, Göring F, Pietruck F, Janssen O, Philipp T, Kribben A. Early detection of acute renal failure by serum cystatin C. Kidney Int. 2004;66:1115–22
2. Darmon M, Schortgen F, Vargas F, Liazydi A, Schlemmer B, Brun-Buisson C, Brochard L. Diagnostic accuracy of Doppler renal resistive index for reversibility of acute kidney injury in critically ill patients. Intensive Care Med. 2011;37:68–76
3. 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;107:891–8
4. Petersen LJ, Petersen JR, Ladefoged SD, Mehlsen J, Jensen HA. The pulsatility index and the resistive index in renal arteries in patients with hypertension and chronic renal failure. Nephrol Dial Transplant. 1995;10:2060–4
5. Platt JF, Ellis JH, Rubin JM, DiPietro MA, Sedman AB. Intrarenal arterial Doppler sonography in patients with nonobstructive renal disease: correlation of resistive index with biopsy findings. AJR Am J Roentgenol. 1990;154:1223–7
6. Platt JF, Rubin JM, Ellis JH, DiPietro MA. Duplex Doppler US of the kidney: differentiation of obstructive from nonobstructive dilatation. Radiology. 1989;171:515–7
7. Kim SH, Byun HS, Park JH, Han JK, Han MC, Lee JS. Renal parenchymal abnormalities associated with renal vein thrombosis: correlation between MR imaging and pathologic findings in rabbits. AJR Am J Roentgenol. 1994;162:1361–5
8. Radermacher J, Chavan A, Schäffer J, Stoess B, Vitzthum A, Kliem V, Rademaker J, Bleck J, Gebel MJ, Galanski M, Brunkhorst R. Detection of significant renal artery stenosis with color Doppler sonography: combining extrarenal and intrarenal approaches to minimize technical failure. Clin Nephrol. 2000;53:333–43
9. Yang PL, Wong DT. Resistive index may not accurately reflect renal flow resistance in the presence of significant aortic insufficiency. Anesth Analg. 2009;109:2033
10. Keogan MT, Kliewer MA, Hertzberg BS, DeLong DM, Tupler RH, Carroll BA. Renal resistive indexes: variability in Doppler US measurement in a healthy population. Radiology. 1996;199:165–9
11. Mangos GJ, Brown MA, Chan WY, Horton D, Trew P, Whitworth JA. Acute renal failure following cardiac surgery: incidence, outcomes and risk factors. Aust N Z J Med. 1995;25:284–9
12. Conlon PJ, Stafford-Smith M, White WD, Newman MF, King S, Winn MP, Landolfo K. Acute renal failure following cardiac surgery. Nephrol Dial Transplant. 1999;14:1158–62
13. Yang PL, Wong DT, Dai SB, Song HB, Ye L, Liu J, Liu B. The feasibility of measuring renal blood flow using transesophageal echocardiography in patients undergoing cardiac surgery. Anesth Analg. 2009;108:1418–24
14. Urban BA, Ratner LE, Fishman EK. Three-dimensional volume-rendered CT angiography of the renal arteries and veins: normal anatomy, variants, and clinical applications. Radiographics. 2001;21:373–86
15. Taori KB, Chaudhary RS, Attarde V, Dhakate S, Sheorain V, Nimbalkar P, Wasnik PN. Renal Doppler indices in sickle cell disease: early radiologic predictors of renovascular changes. AJR Am J Roentgenol. 2008;191:239–42
16. Nelson TR, Fowlkes JB, Abramowicz JS, Church CC. Ultrasound biosafety considerations for the practicing sonographer and sonologist. J Ultrasound Med. 2009;28:139–50

Supplemental Digital Content

Back to Top | Article Outline
© 2013 International Anesthesia Research Society