Hemodynamic monitoring during cardiac surgery is currently based on pressure measurements from an arterial cannula and central venous catheter. While central venous pressure (CVP) is routinely measured during cardiac surgery, the hemodynamic impact of venous hypertension on end-organ perfusion often remains unappreciated. We present a case in which transesophageal echography (TEE) was used to observe the impact of CVP variations on intrarenal venous flow velocities during cardiac surgery. The patient provided written permission for publication of this report.
An 82-year-old woman presented for the progressive onset of angina. Coronary angiography revealed triple vessel disease. She underwent triple coronary artery bypass grafting off-pump. Preoperative echocardiography revealed normal left ventricular systolic function with moderate diastolic dysfunction (grade II) and normal right ventricular function with mild tricuspid regurgitation (grade 1).
After induction of anesthesia, the TEE probe was positioned to obtain a transgastric view of the left kidney during the surgical procedure (Figure 1). A biphasic renal venous flow with a systolic and a diastolic component was noted initially with a CVP measurement of 11 mm Hg (Figure 2A). At that time, the mean arterial pressure to mean pulmonary artery pressure ratio was 4 (65 mm Hg/16 mm Hg). Also, hepatic vein Doppler at the beginning of surgery showed a predominance of the diastolic over the systolic component suggestive of pseudonormal filling (diastolic dysfunction) of the right ventricle.1 In response to those findings, inhaled epoprostenol (75 μg) was administered. Within 25 minutes, the mean arterial pressure/mean pulmonary artery pressure ratio increased to 15 (73 mm Hg/5 mm Hg). During this period, renal venous flow became continuous during the cardiac cycle and CVP decreased to 3 mm Hg (Figure 2B).
During the bypass of the posterior descending artery, the renal venous flow became biphasic again and CVP increased to 6 mm Hg (Figure 3A). At that time, the suspicion of myocardial ischemia during bypass prompted the administration of intravenous nitroglycerin (3 × 20 μg). The CVP decreased to 2 mm Hg within 10 minutes of administration, and renal venous flow returned to a continuous pattern that remained until the end of surgery (Figure 3B). The patient did not develop acute kidney injury or any other complication in the postoperative period.
Extracardiac TEE can be used to assess renal blood flow in real time during cardiac surgery. From a transgastric long-axis view of the heart, the TEE probe is advanced 3–5 cm in the stomach. Turning the probe 90°–180° to the left while maintaining a multiplane angle rotation of 90° will usually result in obtaining a longitudinal view of the spleen followed by the left kidney. The sequence of probe manipulation is seen in the Supplemental Digital Content, Video 1, http://links.lww.com/AACR/A208, associated with this article. An alternate method using a corkscrew pattern is also described by Bandyopadhyay et al.2 The right kidney is not assessable by transgastric TEE in the majority of patients. Color Doppler is used to identify the renal vein flow at the level of the renal hilum, which is color-coded red as the velocity is toward the probe. In our experience, the venous flow velocity at the cortico-medullar junction is <0.2 m/s, more often closer to 0.1 m/s. Therefore, adjustment of the Nyquist limit and exclusion of low-velocity filters are important to record these signals.
In this case, the impact of CVP variations on renal vein flow patterns was observed. Alteration in intrarenal venous flow has been described recently in congestive heart failure patients. In this population, abnormal discontinuous patterns (biphasic with flow in both systole and diastole or monophasic with flow only in diastole) were associated with an increased risk of mortality or hospitalization.3 Furthermore, correction of those abnormal venous patterns could be done using either inhaled agents as previously reported for portal hypertension4 or intravenous agents such as nitroglycerine.
Abnormal patterns of renal venous flow are produced by the transmission of CVP pressure during the cardiac cycle through the noncompliant central venous system as shown in Figure 4. Other conditions affecting venous compliance such as increased intraabdominal and intrathoracic pressure might influence venous flow patterns. However, in open chest condition, increase in intrathoracic and intraabdominal pressure is unlikely to increase CVP. A predominant diastolic hepatic venous flow pattern lacks specificity, because it is recorded in many different etiologies such as atrial fibrillation, tachycardia, constrictive pericarditis, lung disease, moderate tricuspid regurgitation, or right ventricular diastolic dysfunction. The extent to which renal venous flow could be influenced by those factors remain to be determined. Severe right ventricular failure produces changes in the CVP waveform because the limited systolic excursion of the tricuspid annulus results in a reduction of the X descent and prominence of the Y descent. The severe monophasic diastolic pattern of renal venous flow alteration as shown in Figure 4C could be related to the minimal reduction in pressure (no X descent) in the right atrium during systole as right ventricular failure progresses. This pattern is similar to what is seen on the hepatic vein Doppler waveform in the setting of diastolic right ventricular failure.1 However, the renal venous system is much more distal in comparison with the hepatic veins that are direct tributaries of the inferior vena cava. Consequently, the appearance of the renal pattern might require both right ventricular dysfunction and a significant reduction of central venous compliance. In a recent article by Nijst et al,5 it was shown that a volume challenge will worsen the renal venous pattern only in the presence of abnormal cardiac function.
Right ventricular dysfunction can occur in cardiac surgery patients and is associated with a mortality rate up to 22%.6 Organ dysfunction in this setting stems from the combination of a decreased cardiac output and elevated venous pressure resulting in a reduction of the arteriovenous gradient responsible for organ perfusion. While elevated absolute CVP values7 is a known risk factor for acute kidney injury in cardiac surgery, the optimal targets to prevent this complication remain unclear. The use of perioperative extracardiac TEE is enabling clinicians to monitor hemodynamic changes happening directly in end-organs in response to interventions. Whether this information could be used clinically to personalize management and avoid complications remains to be investigated.
Name: William Beaubien-Souligny, MD.
Contribution: This author helped obtain the written consent from the patient, draft the manuscript, and edit the figures and the video.
Conflicts of Interest: None.
Name: André Y. Denault, MD, PhD.
Contribution: This author helped perform the ultrasound assessment and review the manuscript.
Conflicts of Interest: André Y. Denault was a Speaker for Medtronic, CAE Healthcare and Masimo.
This manuscript was handled by: Nikolaos J. Skubas, MD, DSc, FACC, FASE.
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