MAST augmentation of external cardiac compression: role of changing intrapleural pressure.

Ventricular fibrillation was induced in nine dogs weighing 18 to 22 kg. CPR was performed with a mechanical chest compressor. Mean carotid flow during CPR was 7.9 +/- 1.5 ml/min. After MAST inflation to 100 mm Hg, the flow increased to 15.7 +/- 3.7 ml/min. Intrathoracic aortic systolic pressure was also significantly increased from 65 +/- 7 to 73 +/- 8 mm Hg. When the thorax was vented with chest tubes bilaterally, no change in carotid flow or arterial pressure was noted on closing or opening the chest tubes. One liver laceration and two gallbladder contusions were noted at autopsy. MAST inflation apparently augments carotid flow an systolic pressure. Variations in intrapleural pressure do not seem to have a significant influence on CPR.