Pathophysiology of Renal Hemodynamics and Renal Cortical Microcirculation in a Porcine Model of Elevated Intra-abdominal Pressure

Abstract

Elevated intra-abdominal pressure (IAP) has been shown to impair renal perfusion and renal function. This study was designed to further investigate the effects of elevated IAP on renal venous hemodynamics and renal perfusion pressure (RPP). Another aim was to evaluate the renal cortical microcirculation by sidestream dark field (SDF) imaging in a porcine model of elevated IAP. In 11 pigs, IAP was increased stepwise while renal hemodynamics and urinary output were recorded. RPP (RPP = mean arterial pressure minus IAP) and renal filtration gradient (RFG = mean arterial pressure minus 2xIAP) were calculated. Renal cortical microcirculatory perfusion was assessed by calculating the microvascular flow index (MFI) based on SDF data. With IAP elevated to 30 mm Hg, renal arterial and venous flow decreased in parallel by 34% (p < 0.05) and RPP decreased by 12% (p < 0.05). With increasing IAP, renal vascular resistance increased and MFI decreased significantly. RFG showed a moderate correlation with renal blood flow (r = 0.39, p < 0.05) and MFI (r = 0.46, p < 0.005), whereas RPP did not. In a porcine model of IAP-induced renal impairment, we observed a parallel decrease in renal venous and arterial blood flow together with blood flow redistribution away from the kidney. SDF imaging was used for the first time to assess renal cortical microcirculation and MFI was found to decrease with increasing IAP. RFG, as a clinical estimator of renal perfusion, correlated moderately with renal blood flow and microcirculatory perfusion, whereas RPP did not. Increased renal vascular resistance with elevated IAP might account for this.