Blood flow distribution during elevated intraperitoneal pressure in the rat

Aim:  Oliguria is seen during elevated intraperitoneal pressure, but the physiological mechanisms are not yet clarified. The purpose of the present study was to investigate the changes in renal function, cardiac output and distribution of systemic blood flow (BF) that occur in connection with an elevation of intra-abdominal pressure (IAP) in a rat model by isotope-labelled microsphere technique. Methods:  A 5 or 10 mmHg IAP was created by CO2 insufflation and maintained for 90 min in anaesthetized and mechanically ventilated rats. Rats with normal IAP served as controls. Blood flow and cardiac output measurements by injection of isotope-labelled microspheres were conducted at three time points. Acid–base balance, urine output, glomerular filtration rate (GFR) and urinary excretion products were also followed. Results:  Glomerular filtration rate decreased [0.7–0.1 mL min−1 g−1 kidney weight (KW)] with elevated IAP, as did urine output (8.5–0.6 μL min−1 g−1 KW). Dramatic decreases were seen in renal excretion of sodium (by 97%), potassium (by 94%) and osmotic active substances (by 93%). Cardiac output was diminished by 54% at 5 mmHg and by 65% at 10 mmHg intraperitoneal pressure and systemic vascular resistance (SVR) was elevated threefold. Conclusion:  Cardiac output, measured by microsphere technique, decreased during elevated intraperitoneal pressure by CO2 in anaesthetized rats, while SVR was elevated and renal excretory functions were decreased to a large extent.