Immediate hemodynamic consequences of MAST inflation in normo- and hypovolemic anesthetized swine

Use of the military antishock trouser (MAST) remains controversial in part because its mechanism(s) of action are poorly understood. We studied two aspects of the hemodynamic response to MAST inflation in 14 anesthetized swine. First, in six swine the relation that existed between inferior vena cava flow and aortic pressure/cardiac output was determined before and during inflation of the MAST, and then before and after removal of 30% of the calculated blood volume. Inflation of the MAST before hemorrhage had little effect on cardiac output but increased aortic pressure by 25%. Inflation of the MAST after hemorrhage increased cardiac output by 41% and increased aortic pressure by 62%. Three different inflation pressures were studied (40, 80, and 120 mm Hg) and were found to give equivalent results. Inflation of the MAST translocated about 3 ml/kg of blood to the heart. A second group of eight swine were instrumented so that the radiomicrosphere technique could be used to measure organ blood flow. Inflation of the MAST following hemorrhage increased coronary perfusion by 50% and cerebral perfusion by about one third. Flow to kidney, liver, and small intestine was not changed. We conclude that, in addition to tamponade of venous bleeding and the splinting of lower extremity fractures, use of the MAST might cause a clinically important increase in the perfusion of the heart and brain in some trauma patients.