Renal arterial resistive index response to intraabdominal hypertension in a porcine model*

Abstract

The abdominal compartment syndrome is a potentially life-threatening condition with frequent renal involvement. There are few if any means of inferring subclinical effects before organ dysfunction. Because intrarenal pressure correlates with renal sonographic indices in other renal diseases, the purpose of this study was to determine the relationship between increasing intraabdominal hypertension and renal vascular flow velocities in a porcine model using renal Doppler ultrasound. Animal study. University research laboratory. Eight anesthetized, mechanically ventilated, well-hydrated, 30-kg female Yorkshire pigs. Intraabdominal hypertension was induced by instillation of warmed intraperitoneal saline through a midline laparoscopic port. Intraabdominal pressure (IAP) was continuously monitored directly from the peritoneum and indirectly from the bladder. IAP was varied from 0 to 50 mm Hg in increments of 5 mm Hg. At each IAP level, gray-scale, color, and spectral Doppler renal arcuate artery ultrasound was obtained and resistive index (RI) and peak airway pressure calculated. Excellent agreement between direct and indirect IAP was found (bias, 0.032 mm Hg; 95% limits, -5.5 to 5.6 mm Hg). A linear relationship between RI and indirect IAP was observed and was defined by the regression equation: RI = 0.553 + 0.0104 x bladder pressure. There was a trend toward different RIs between left and right kidneys (p = .052) at the same IAP. RI varied in a linear fashion at low peak airway pressure and demonstrated an inflection point with steeper subsequent slope after peak airway pressure of 30 cm H2O. RI values rapidly returned to near baseline after abdominal decompression. In this model, the renal artery RI correlated strongly and linearly with the severity of intraabdominal hypertension, making renal Doppler ultrasound a potential noninvasive screening tool for the renal effects of intraabdominal hypertension. Further studies are warranted.