Intraoperative transesophageal ultrasonography can measure renal blood flow

Abstract

Objective: To determine the feasibility of acquiring Doppler-derived indices of renal blood flow by transesophageal ultrasonography in the perioperative period. Design: Prospective, sequential, institutional review board—approved study. Setting: University teaching hospital. Participants: Nine patients with normal renal function, scheduled for elective primary coronary artery bypass graft surgery. Interventions: Two-dimensional images of renal parenchyma and Doppler measurement of intrarenal arterial blood flow during internal mammary dissection were acquired. To effect renal blood flow changes, the renal vasodilator dopamine, 2 μg/kg/min, was infused for 20 minutes after baseline measurements were made. Renal Doppler measurements were repeated to determine whether transesophageal ultrasonography can follow these changes. Measurements and Main Results: Hemodynamic measurements (heart rate, mean arterial blood pressure, cardiac output, and cardiac index) and Doppler velocity measurements of intrarenal arterial blood flow (peak systolic, end-diastolic, and mean velocity) were made at time 1 (T1 = baseline) and at time 2 (T2 = after 20 minutes of dopamine infusion). The derived Doppler indices, pulsatility index and resistive index, were calculated according to standard formulae. Measurements were compared by paired Student's t-test (two-tailed, p < 0.05, significant). There were no statistical differences between cardiac index (2.10 ± 0.93 L/min/m2v 2.21 ± 0.92 L/min/m2, p = 0.254) and mean arterial pressure (82.3 ± 11.2 mmHg v 83.3 ± 14.5 mmHg, p = 0.872) between T1 and T2. Systolic renal velocity increased from 44.7 ± 13.0 cm/s to 63.0 ± 20.4 cm/s (p = 0.005), diastolic velocity increased from 12.7 ± 4.0 cm/s to 22.4 ± 7.8 cm/s (p = 0.0003), and mean velocity increased from 22.5 ± 6.6 cm/s to 34.1 ± 11.7 cm/s (p = 0.003) after infusion of dopamine. These results indicate an increase in renal blood flow from baseline values. The pulsatility index decreased from 1.44 ± 0.29 to 1.21 ± 0.24 (p = 0.0005), whereas the resistive index decreased from 0.71 ± 0.06 to 0.64 ± 0.06 (p = 0.0004) after dopamine. Reductions in pulsatility and resistive indices indicate a reduction in renal vascular resistance. Conclusion: This study demonstrates the ability to acquire two-dimensional images of kidney and renal arterial Doppler velocities using transesophageal ultrasonography during cardiac surgery. Transesophageal renal arterial Doppler waveform analysis can follow changes in renal blood flow patterns secondary to interventional therapy. Copyright © 2001 by W.B. Saunders Company