Physiologic effects of externally applied continuous negative abdominal pressure for intra-abdominal hypertension

Background: To determine the ability of an externally applied continuous negative abdominal pressure device (CNAP) to reverse the effects of elevated intra-abdominal pressure on the central nervous and cardiovascular systems. Methods: Anesthetized, ventilated swine had catheters placed for measurement of intra-abdominal (IAP), intracranial (ICP), central venous, pulmonary artery, pulmonary artery occlusion, mean arterial, peak inspiratory, inferior vena cava, and femoral vein pressures. After the animals stabilized, baseline measurements were obtained. IAP was increased by incrementally in stilling an isosmotic polyethylene glycol solution into the peritoneal cavity until it was 25 mm Hg above baseline. IAP mas maintained at 25 mm Hg above baseline for 2 hours. CNAP was then applied for 2 hours. All parameters were remeasured 30 minutes after each increase in WP, at 2 hours after attaining maximum IAP, and lastly at 2 hours after abdominal decompression. Cardiac index was maintained near baseline by volume expansion. Results: Elevation of WP to 25 mm Hg above baseline for 2 hours caused increases (p < 0.05) in central venous pressure (10.3 +/- 0.9 to 15.2 +/- 1.7), inferior vena cava pressure (13.0 +/- 1.0 to 29.5 +/- 1.5), femoral vein pressure (13.5 +/- 0.5 to 33.3 +/- 1.3), ICP (10.6 +/- 1.5 to 21.0 +/- 1.5), and peak inspiratory pressure (18.3 +/- 0.3 to 34.2 +/- 1.0). The mean arterial pressure (106.3 +/- 3.5 to 125.8 +/- 3.4), pulmonary artery pressure (24.3 +/- 2.3 to 31.3 +/- 1.7), and pulmonary artery occlusion pressure rose (12.3 +/- 0.9 to 17.5 +/- 3.5), but not significantly. Cardiac index (3.3 +/- 0.5 to 3.4 +/- 0.4) remained essentially unchanged. CNAP significantly (p < 0.05) decreased IAP (30.7 +/- 1.3 to 18.2 +/- 1.3), central venous pressure (15.2 +/- 1.7 to 12.4 +/- 2.1), inferior vena cava (29.5 +/- 1.5 to 19.2 +/- 1.3), and ICP (21.0 +/- 1.5 to 16.2 +/- 1.3). Pulmonary artery occlusion pressure (17.5 +/- 3.5 to 15.0 +/- 3.1) and peak inspiratory pressure (34.2 +/- 1.0 to 29.7 +/- 1.1) decreased, but not significantly. Conclusion: Acutely elevated IAP causes a significant increase in ICP and impaired cardiovascular and pulmonary function, Abdominal decompression remains the standard of care for abdominal compartment syndrome. However, in patients in whom an increased WP does not require surgical decompression, the results of this study suggest that externally applied CNAP may be of value.