CPR with simultaneous compression and ventilation at high airway pressure in 4 animal models.

CPR with simultaneous chest compression and ventilation at high airway pressure (SCV-CPR) improves blood flow in some studies but not in others, perhaps because of differences in the animal models employed. To resolve such discrepancies, we compared SCV-CPR to standard CPR in 4 mechanically different canine models, using both small and large dogs and small and large compression pads. The 4 groups were: large dogs receiving chest compression through a large pad (model A), large dogs receiving chest compression through a small pad (model B), small dogs receiving chest compression through a large pad (model C), and small dogs receiving chest compression through a small pad (model D). Cardiac output (CO) during CPR was determined by a specially modified indicator dilution method. Models A, B, and C all had similar mean COs of 14 ml/min . kg body weight during standard CPR, and 27 ml/min . kg during SCV-CPR. However, in model D, there was no significant difference during standard vs. SCV-CPR, and the mean output was 33 ml/min . kg. We conclude that in models A, B, and C, little direct heart compression occurred and the higher intrathoracic pressure pulses produced by SCV-CPR improved blood flow. However it seems likely that there was effective cardiac compression in model D. In the absence of direct cardiac compression, SCV-CPR provides an alternative means of generating satisfactory flow in a mechanically appropriate animal model.