Cardiopulmonary effects of raised intra-abdominal pressure before and after intravascular volume expansion

The cardiopulmonary effects of acutely elevated intra-abdominal pressure (IAP) were studied in a porcine model to help define more clearly IAP effects in patients with trauma. IAP was increased in six anesthetized swine by intra-abdominal instillation of isotonic ethylene glycol up to an IAP of 25 mm Hg above baseline. Systemic and pulmonary hemodynamic parameters were measured, as well as the effects on bladder pressure, pleural pressure, and pulmonary function. At IAP of 25 mm Hg above baseline, intravascular volume expansion with saline was administered to return the cardiac index (CI) to baseline. Raising IAP correlated with measured bladder pressures (r = 0.9, p = 0.001). At IAP of 25 mm Hg, CI was significantly decreased (p < 0.05, analysis of variance (ANOVA); 3.6 +/- 0.3 vs. 2.2 +/- 0.3 L/min/m2); whereas wedge, pulmonary arterial, and pleural pressures were all elevated (p < 0.05, ANOVA). However, transarterial wedge pressure (wedge--pleural pressure) declined nonsignificantly with increasing IAP. Raised IAP caused impaired pulmonary function with a decreased (p < 0.05, ANOVA) PaO2 and increased (p < 0.05, ANOVA) PaCO2. Despite the elevated wedge pressure, fluid resuscitation returned CI to baseline. These data clarify the hemodynamic changes associated with raised IAP and indicate that care must be taken in interpreting hemodynamic measurements to determine intravascular fluid status in patients with elevated IAP.