Laparoscopy is used increasingly in managing critically ill patients. Carbon dioxide (CO 2 ) pneumoperitoneum is used during these procedures. The increased intra-abdominal pressure of CO 2 pneumoperitoneum, however, can affect cardiopulmonary performance adversely. Recently, gasless abdominal wall distention has been introduced as an alternative to CO 2 pneumoperitoneum. The purpose of this study was to compare the hemodynamic effects of gasless abdominal distention (GAD) with those of CO 2 pneumoperitoneum during mechanical ventilation with positive end-expiratory pressure (PEEP). Six anesthetized, paralyzed, mechanically ventilated adult swine were monitored with pulmonary artery and arterial catheters at incremental values of PEEP (0-20 cm H 2 0, by 5, Control) and then allowed to return to baseline hemodynamic status at 0 cm H 2 O PEEP. The animals were then randomly assigned to receive either CO 2 pneumoperitoneum at 15 mm Hg intra-abdominal pressure (PNEUMO) or GAD (equal to anterior abdominal wall displacement of CO 2 ) and PEEP was reapplied. The animals were allowed to return to hemodynamic baseline and PEEP was reapplied with the alternate method of abdominal wall distention. A complete hemodynamic profile and arterial/ mixed venous blood gas measurements were monitored at each value of PEEP. With GAD, central venous pressure (CVP), pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP), and P a CO 2 were significantly reduced, compared to PNEUMO, and P a O 2 was increased. Cardiac index was higher in GAD versus PNEUMO at baseline, but was lower for GAD at PEEP levels above 10 cm H 2 O. These results indicate that in its net effect, GAD does not exacerbate the adverse hemodynamic effects of PEEP. This technique may be a favorable alternative to CO 2 pneumoperitoneum in the critically ill ventilated patient when there is concern over PAP, CVP, PCWP, and P a O 2 /P a CO 2 .