Relative effectiveness of interposed abdominal compression CPR: sensitivity analysis and recommended compression rates.
UNLABELLED: Interposed abdominal compression, IAC-CPR incorporates alternating chest and abdominal compressions to generate enhanced artificial circulation during cardiac arrest. The technique has been generally successful in improving blood flow and survival compared to standard CPR; however, some questions remain. OBJECTIVE: To determine "why does IAC-CPR produce more apparent benefit in some subjects than in others?" and "what is the proper compression rate, given that there are actually two compressions (chest and abdomen) in each cycle?" METHOD: Computer models provide a means to search for subtle effects in complex systems. The present study employs a validated 12-compartment mathematical model of the human circulation to explore the effects upon systemic perfusion pressure of changes in 35 different variables, including vascular resistances, vascular compliances, and rescuer technique. CPR with and without IAC was modeled. RESULTS AND CONCLUSIONS: Computed results show that the effect of 100 mmHg abdominal compressions on systemic perfusion pressure is relatively constant (about 16 mmHg augmentation). However, the effect of chest compression depends strongly upon chest compression frequency and technique. When chest compression is less effective, as is often true in adults, the addition of IAC produces relatively dramatic augmentation (e.g. from 24 to 40 mmHg). When chest compression is more effective, the apparent augmentation with IAC is relatively less (e.g. from 60 to 76 mmHg). The optimal frequency for uninterrupted IAC-CPR is near 50 complete cycles/min with very little change in efficacy over 20-100 cycles/min. In theory, the modest increase in systemic perfusion pressure produced by IAC can make up in part for poor or ineffective chest compressions in CPR. IAC appears relatively less effective in circumstances when chest pump output is high.