External cardiopulmonary resuscitation augmented by the military antishock trousers.

The external pressure suit (MAST) is beneficial in hypovolemic shock by preventing lower extremity venous pooling. Previous data from this laboratory demonstrated that internal cardiac massage is significantly improved when combined with MAST. This study was designed to see if external massage (EM) could be similarly augmented by this device. Twenty anesthetized pigs underwent left thoracotomy and placement of a left atrial catheter for pressure determination and microsphere injection. A flow probe was placed around the aorta for measurement of cardiac output, axillary artery catheters were placed for blood pressure determination and microsphere sampling, and central venous pressure was monitored. Hemodynamic collection of microsphere injections was performed during resting conditions, during EM alone after electrically induced ventricular fibrillation, and during EM after inflation of the MAST suit. Significant increases in mean arterial pressure, systolic arterial pressure, and diastolic pressure were noted with EM and MAST suit inflation over EM alone. Left atrial pressure doubled during EM and MAST suit inflation. Cardiac output was not augmented by the inflation of the MAST. Myocardial blood flow and brain blood flow increased during EM and MAST, but renal blood flow decreased. These data suggest that unlike internal massage, cardiac output during EM and MAST is not improved by increased venous return and flow during EM may be due to a different mechanism than direct cardiac compression.