Evaluation of decapsulation of the canine kidney on renal function following acute ischemia

Intra-abdominal hypertension: evolving concepts

This article focuses primarily on the recent literature on abdominal compartment syndrome (ACS) and the definitions and recommendations published by the World Society for the Abdominal Compartment Syndrome. The definitions regarding increased intra-abdominal pressure (IAP) are listed and are followed by an overview of the different mechanisms of organ dysfunction associated with intra-abdominal hypertension (IAH). Measurement techniques for IAP are discussed, as are recommendations for organ function support and options for treatment in patients who have IAH. ACS was first described in surgical patients who had abdominal trauma, bleeding, or infection; but recently, ACS has been described in patients who have other pathologies. This article intends to provide critical care physicians with a clear insight into the current state of knowledge regarding IAH and ACS.

Pathophysiology of renal hemodynamics and renal cortical microcirculation in a porcine model of elevated intra-abdominal pressure

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Renal blood flow and intrarenal distribution of blood flow after decapsulation in the postischemic kidney

Previous reports suggest the value of renal decapsulation in the prevention of renal failure after acute ischemia. It has been suggested that this response is due to a release of "compartmental" pressure resulting in increased blood flow to the decapsulated kidney. Ten dogs were evaluated following 90 minutes of renal ischemia created by occlusion of the suprarenal aorta. Each animal underwent random unilateral decapsulation, with the contralateral kidney acting as control. Labeled 15 micron microspheres (Se85 and Ce141) were injected into the left ventricle at 15 minutes and one hour following decapsulation in six dogs. In the remaining animals the injection was carried out at 15 minutes and 48 hours. No difference in renal blood flow was found between decapsulated and control kidneys in either group. Similarly, using sectioned kidneys no difference in intrarenal distribution of blood flow was found. These data suggest that the effects caused by decapsulation are not due to hemodynamic alterations.