Venous return in hemorrhagic shock after application of military anti-shock trousers

The effect of Military Anti-Shock Trousers (MAST) on inferior vena cava blood flow was studied during graded hypovolemia using a pump reservoir system and an in-line electromagnetic flowprobe. During hemorrhagic shock MAST inflation increased cardiac output 25.4% (

0.92 +/- 0.09 l/min) and arterial pressure 50% (

60 +/- 2 mmHg). The so-called "autotransfusion" effect due to blood displacement from the lower part of the body into the central circulation was found to be only 4.3 +/- 0.6 ml/kg, a volume much less than previously estimated in the literature. We conclude that MAST inflation reliably improves cardiac output and systemic blood pressure above the diaphragm in dogs subjected to hemorrhagic shock. This effect is mainly due to a diversion of the cardiac output to the upper half of the body due to impedance of flow to the abdomen and lower extremities, rather than to a significant volume shift constituting an autotransfusion of blood from the lower part of the body.