Extremity compartment syndrome in pigs during hypobaric simulation of aeromedical evacuation

Introduction: Extremity compartment syndrome (ECS) is diagnosed when the pressure within a muscle compartment increases to within 45 mmHg of mean arterial pressure. Increased pressure limits perfusion and eventually produces tissue necrosis. This can result in disability or loss of the affected limb. Hypobaric pressure during aeromedical evacuation (AE) has been hypothesized to increase the incidence of ECS. This was tested in a threshold model of ECS in swine. Methods: Injury was induced by placing an angioplasty balloon between the tibia and the anterior muscle compartment and infl ating the balloon to produce an intracompartmental pressure (ICP) 30 mmHg greater than mean arterial pressure for either 5 h or 6 h. Afterwards, animals were maintained either at ground level pressure or at a pressure equivalent to a simulated altitude of 2135 m above sea level for 8 h. ICP was monitored for signs of ECS development. At the end of the period the muscle was collected and evaluated for pathological changes and expression of various molecules associated with infl ammation and tissue injury. Results: Simulated altitude did not increase incidence of ECS, peak intracompartmental pressures, or time to onset of ECS. However, muscle degeneration and formation of microvascular thrombi were reduced by exposure to altitude. TNF, IL-1 b, IL-6, IGFBP5, and TGFB2 were increased ( P , 0.05) by exposure to altitude, whereas FGF, IGF1, IGFBP4, BMP4, nitrotyrosine, and nitrate were unchanged (P<0.05). Discussion: Simulated altitude did not increase incidence of ECS. Infl ammatory protein expression was increased in muscle, but some aspects of pathology were less severe following altitude exposure.