ELEVATED INTRAABDOMINAL PRESSURE INCREASES PLASMA-RENIN ACTIVITY AND ALDOSTERONE LEVELS

Objective: To study the effects of elevated intra-abdominal pressure u pon renal function and the renin-angiotensin-aldosterone system. Mater ials and Methods: Two groups of anesthetized, ventilated swine were st udied, Intra-abdominal pressure was increased in experimental animals (n = 6) by incrementally instilling an isosmotic ethylene glycol solut ion into the peritoneal cavity until intra-abdominal pressure was 25 m m Hg above baseline, The intravascular volume was then expanded until cardiac index returned to baseline, Lastly, the solution was drained t o decompress the abdomen, Control animals underwent surgical preparati on but did not have their intra-abdominal pressure raised, Changes in systemic and pulmonary hemodynamic parameters, renal venous pressure, and urine output were recorded, Venous samples for plasma renin activi ty, aldosterone, and atrial natriuretic factor were drawn after each c hange in either intra-abdominal pressure or intravascular volume in ex perimental animals, and at the same time points in control animals. Me asurements and Main Results: Elevated intra-abdominal pressure signifi cantly (p < 0.05, analysis of variance) increased renal venous pressur e, pleural pressure, wedge pressure, and pulmonary artery pressure com pared to both baseline and control animals; whereas cardiac index and urine output decreased significantly, Both plasma renin and aldosteron e levels increased significantly compared with baseline and controls, Intravascular volume expansion significantly increased urine output an d decreased significantly both plasma renin activity and aldosterone l evels, Abdominal decompression further significantly decreased both pl asma renin activity and aldosterone levels, There were no significant changes in atrial natriuretic factor at any time point. Conclusions: E levated intra-abdominal pressure decreases urine output and significan tly up-regulates the hormonal output of the renin-angiotensin-aldoster one system. Intravascular volume expansion in combination with abdomin al decompression reverses the effects of acutely elevated intra-abdomi nal pressure upon renal function and the renin-angiotensin-aldosterone system.