Intra-abdominal hypertension, prone ventilation, and abdominal suspension.

Despite basic laboratory work suggesting inherent physiologic rationale and particular attraction for use among the most critically ill subgroups with either acute lung injury or adult respiratory distress syndrome (ARDS), prospective trials of prone ventilation (PV) have been unable to demonstrate treatment effects on mortality.1,2 Although the exact physiology of improvements in gas exchange with PV remains complex and controversial, this technique was originally suggested as a simple means of alleviating intrusion of the intraabdominal contents on the thoracic volume.3 In the obese, it is felt to be important to freely suspend the abdominal cavity, with the thoracoabdominal weight supported on the chest and pelvic bones. This unloading of the lung bases markedly improves relative pulmonary function.4 Unfortunately, prospective trials of PV in acute lung injury/ARDS have not either considered or reported this factor. We recently encountered a morbidly obese (414 pounds, 5 foot 2 inches) patient with a surgical emergency. Her intraabdominal pressures (IAP) reflected a preexisting compliant abdomen with a preoperative IAP of 10 mm Hg, despite possessing an incarcerated incisional hernia with a perforated and ischemic colon. This required a resection, anastomosis, and bioprosthetic abdominal wall reconstruction. Unfortunately, her course was complicated by ARDS and intraabdominal hypertension to 20 mm Hg.5 As her gas exchange worsened, she was initially proned without suspension. This resulted in worsening intraabdominal hypertension to 24 mm Hg, with concurrent peak airway pressure of 44 cm · H2O. After suspension and abdominal unloading, however, her IAPs decreased progressively to 23, 21, 17, and 14 mm Hg over the subsequent 4 hours (peak airway pressures also decreased to 38, 27, 25, and 22 cm · H2O, respectively). They remained at 14 mm Hg for the following 72 hours. As she improved, her intraabdominal hypertension resolved (IAP <12 mm Hg), and she was thereafter able to ventilate in the supine position. She was ultimately discharged to a rehabilitation facility independent of mechanical ventilation. Our experience with this case has prompted us to reflect on the belief that the abdominal condition and positioning seems to be critical to the technique of PV. We think this issue needs to be raised in the future to allow for proper evaluation of the potential merits of the PV technique.