Elevated Intra-abdominal Pressure Increases Plasma Renin Activity and Aldosterone Levels

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Abstract
To study the effects of elevated intra-abdominal pressure upon renal function and the renin-angiotensin-aldosterone system. Two groups of anesthetized, ventilated swine were studied. Intra-abdominal pressure was increased in experimental animals (n = 6) by incrementally instilling an isosmotic ethylene glycol solution into the peritoneal cavity until intra-abdominal pressure was 25 mm Hg above baseline. The intravascular volume was then expanded until cardiac index returned to baseline. Lastly, the solution was drained to decompress the abdomen. Control animals underwent surgical preparation 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 activity, aldosterone, and atrial natriuretic factor were drawn after each change in either intra-abdominal pressure or intravascular volume in experimental animals, and at the same time points in control animals. Elevated intra-abdominal pressure significantly (p < 0.05, analysis of variance) increased renal venous pressure, pleural pressure, wedge pressure, and pulmonary artery pressure compared to both baseline and control animals; whereas cardiac index and urine output decreased significantly. Both plasma renin and aldosterone levels increased significantly compared with baseline and controls. Intravascular volume expansion significantly increased urine output and decreased significantly both plasma renin activity and aldosterone levels. Abdominal decompression further significantly decreased both plasma renin activity and aldosterone levels. There were no significant changes in atrial natriuretic factor at any time point. Elevated intra-abdominal pressure decreases urine output and significantly up-regulates the hormonal output of the renin-angiotensin-aldosterone system. Intravascular volume expansion in combination with abdominal decompression reverses the effects of acutely elevated intra-abdominal pressure upon renal function and the renin-angiotensin-aldosterone system.