Effects of intra-abdominal pressure on respiratory system mechanics in mechanically ventilated rats.

We investigated the effects of intra-abdominal pressure on respiratory system compliance at different PEEP levels. 20 ventilated rats underwent four pressure levels (7, 9, 11, 13 mm Hg) of helium pneumoperitoneum and were allocated to one of the four PEEP groups (0, 3, 6 and 9 cm H(2)O). From the expiratory pressure-volume curve the mathematical inflection point (MIP) was calculated. Volume-dependent compliance was analyzed using the SLICE-method. MIP-pressure correlated to the intra-abdominal pressure (r(2)=0.94, p<0.001). Peak inspiratory pressure increased with intra-abdominal pressure, and was lower after recruitment-maneuvers (p<0.001). The compliance gain following recruitment-maneuvers depended on PEEP, intra-abdominal pressure and intratidal volume (all p<0.001). Mean arterial pressure was independent of PEEP (p=0.068) and intra-abdominal pressure (p=0.293). Volume-dependent compliance courses varied according to PEEP and intra-abdominal pressure. The level of intra-abdominal pressure alters respiratory system mechanics in healthy lungs. Intratidal compliance can be used to guide the PEEP adjustment in intra-abdominal hypertension. If counterbalanced by PEEP, elevated intra-abdominal pressure has no negative effects on oxygenation or hemodynamics.