Alterations in Portal Vein Flow and Intrarenal Venous Flow Are Associated With Acute Kidney Injury After Cardiac Surgery: A Prospective Observational Cohort Study

Abstract

Background Acute kidney injury ( AKI ) after cardiac surgery is associated with adverse outcomes. Venous congestion can impair kidney function, but few tools are available to assess its impact at the bedside. The objective of this study was to determine whether portal flow pulsatility and alterations in intrarenal venous flow assessed by Point-Of-Care ultrasound are associated with AKI after cardiac surgery. Methods and Results This single-center prospective cohort study recruited patients undergoing cardiac surgery with cardiopulmonary bypass. Hepatic and renal Doppler ultrasound assessments were performed before surgery, at the intensive care unit admission, and daily for 3 days after surgery. The primary statistical analysis was performed using proportional hazards model for time-dependent variables. Among the 145 patients included, 49 patients (33.8%) developed AKI after cardiac surgery. The detection of portal flow pulsatility was associated with an increased risk of AKI (hazard ratio: 2.09, confidence interval, 1.11-3.94, P=0.02), as were severe alterations of intrarenal venous flow (hazard ratio: 2.81, confidence interval, 1.42-5.56, P=0.003). These associations remained significant in multivariable models. The addition of these markers to preoperative risk factors and central venous pressure measurement at intensive care unit admission improved the prediction of AKI . (Continuous net reclassification improvement: 0.364, confidence interval, 0.081-0.652 for portal Doppler and net reclassification improvement: 0.343, confidence interval, 0.081-0.628 for intrarenal Doppler) Conclusions Portal flow pulsatility and intrarenal flow alterations are markers of venous congestion and are independently associated with AKI after cardiac surgery. These tools might offer valuable information to develop strategies aimed at treating or preventing congestive cardiorenal syndrome after cardiac surgery. Clinical Trial Registration URL : https://www.clinicaltrials.gov . Unique identifier: NCT 02831907.

Keywords: acute kidney injury; cardiac surgery; congestive heart failure; point‐of‐care ultrasound.

Figure 1

Pulse‐wave Doppler assessment of portal vein flow by transthoracic ultrasound. A, Probe position in the mid to posterior axillary position shown using the Vimedix simulator (with permission of CAE Healthcare, St‐Laurent, Canada). B, Color Doppler of hepatic vessels showing the position of the hepatic vein (HV) and the portal vein (PV). C, Normal portal flow showing minimal variations of flow velocities during the cardiac cycle (pulsatility fraction: 18.4%). D, Abnormal variations of portal flow velocities during the cardiac cycle (pulsatility fraction: 66%). E, Normal hepatic vein waveform with systolic component (S) equal to or greater than the diastolic component (D). F, Abnormal hepatic venous flow with systolic component (S) less than the diastolic component and, (E), when severe, with reversal of hepatic flow during systole. PG indicates pressure gradient; RPV, right portal vein; Vel, velocities.

Figure 2

Doppler assessment of renal interlobar arterial and venous flow by transabdominal echography. A, Probe position in the posterior axillary position to obtain a longitudinal view of the right and left kidney shown using the Vimedix simulator (with permission of CAE Healthcare, St‐Laurent, Canada). B, Longitudinal view of the right kidney with color Doppler to identify interlobar vessels. The intrarenal venous waveform was classified into 3 patterns. Pattern 1: (C) Normal continuous venous flow during the cardiac cycle or brief interruption of venous flow during atrial contraction. Pattern 2: (D) Discontinuous biphasic venous flow with systolic and diastolic components. Pattern 3: (E) Discontinuous venous flow with flow exclusively detectable during diastole.

Figure 3

Flowchart of studied patients. AKI indicates acute kidney injury; ECMO, extracorporal membrane oxygenation; TAVR, transcatheter aortic valve replacement.

Figure 4

Portal and intrarenal venous flow during the perioperative period. A, Portal flow pulsatility (PF≥50%). B, Intrarenal venous flow patterns. C, Measured portal pulsatility fraction (PF) according to intrarenal flow patterns. D, Proportion of assessments showing concordance or discordance between abnormal portal flow (PF≥50%) or abnormal intrarenal venous patterns (Pattern >1) *Significant difference P<0.05. POD indicates postoperative day.

Figure 5

Acute kidney injury (AKI)–free survival according to (A) portal Doppler patterns and (B) intrarenal venous flow patterns at the intensive care unit (ICU) admission after cardiac surgery. The association between each ultrasound finding and AKI was determined by univariate Cox regression and the results are presented adjacent to the survival curves as hazard ratio (HR) with 95% confidence intervals (CI). PF indicates pulsatility fraction of the portal vein.

Figure 6

Reclassification plots illustrating the added value of the studied ultrasound markers compared with a baseline risk prediction model of acute kidney injury (AKI). A, New model with the addition of portal flow pulsatility at ICU admission. B, New model with the addition of severe intrarenal venous flow alteration at ICU admission. AKI cases above the reference line and non‐AKI cases below the reference are appropriately reclassified in the new model. For both analyses, the baseline model was composed of preoperative risk factors (AKI risk score13 and intervention on thoracic aorta) and central venous pressure measurement at ICU admission. ICU indicates intensive care unit.