Continuous external counterpressure during closedchest resuscitation

Blood flow during closed-chest CPR may result from variations in intrathoracic pressure rather than selective compression of the cardiac ventricles. During chest compression, the thoracic and abdominal cavities are subjected to positive pressure fluctuations. It has been suggested that compression of the abdomen may improve left heart outflow during CPR by limiting diaphragmatic movement or improving venous return. Abdominal compression has been performed experimentally with pneumatic abdominal binders and with the abdominal compartment of the conventional military antishock trouser (MAST) garment. The MAST garment might also improve cardiac output with CPR through an “autotransfusion” effect. In animal studies, MAST-augmented CPR has improved systolic pressures; it has not been shown to improve vital organ perfusion. In the only available clinical study, CPR with the MAST did not improve survival from prehospital cardiac arrest when compared with conventional CPR alone. If inflation of the MAST does produce blood displacement from the peripheral to the central venous circulation, such an effect may be detrimental in that the arteriovenous pressure gradients necessary for vital organ flow may be adversely affected. Inflation of the MAST during CPR may also adversely effect artificial ventilation. Selective abdominal binding also increases systolic pressures during CPR but does not improve subdiaphragmatic venous return. Although abdominal binding may increase common carotid flow, it has not been shown to improve cerebral or myocardial perfusion when compared with conventional CPR alone. These CPR adjunct techniques have not been shown to improve outcome from cardiac arrest and should remain experimental until further welldesigned studies addressing regional vital organ flow and outcome of resuscitation are performed.