Effects of compression rate and compression/Relaxation ratio on the hemodynamics of simultaneous sterno-thoracic cardiopulmonary resuscitation in the canine model of cardiac arrest

Study objectives: This study is designed to determine the compression rate and the compression:relaxation ratio to produce the optimal hemodynamic effect with simultaneous sternothoracic cardiopulmonary resuscitation (SST-CPR) and to investigate the mechanism for the blood flow generated by SST-CPR. Methods: A canine model of ventricular fibrillation was used. Twelve mongrel dogs were divided into 2 groups. In the first, 6 animals were resuscitated by using SST-CPR with the compression duration varied randomly at 2-minute intervals, 30%, 40%, and 50% of the CPR cycle, at a constant rate of 80/minute. In the other 6 dogs, SST-CPR was performed with a randomly varied compression rate, 60, 80, 100, and 120/minute, at a 50:50 compression:relaxation ratio. Results: During SST-CPR, increasing the compression:relaxation ratio from 30:70 to 50:50 increased the end-tidal CO2from 10±2 mm Hg to 15±3 mm Hg. Increasing the compression rate from 60 to 100/minute tended to improve the carotid blood flow. Conclusion: The maximal hemodynamic effect with SST-CPR was generated when the compression rate was 100/minute and the compression:relaxation ratio was 50:50. A combination of the cardiac and the thoracic pump theories may be the mechanism for the blood flow produced by SST-CPR.