Survival and neurologic outcome after cardiopulmonary resuscitation with four different chest compression-ventilation ratios

Study objective: The optimal ratio of chest compressions to ventilations during cardiopulmonary resuscitation (CPR) is unknown. We determine 24-hour survival and neurologic outcome, comparing 4 different chest compression-ventilation CPR ratios in a porcine model of prolonged cardiac arrest and bystander CPR. Methods: Forty swine were instrumented and subjected to 3 minutes of ventricular fibrillation followed by 12 minutes of CPR by using 1 of 4 models of chest compression-ventilation ratios as follows: (1) standard CPR with a ratio of 15:2; (2) CC-CPR, chest compressions only with no ventilations for 12 minutes; (3) 50:5-CPR, CPR with a ratio of 50:5 compressions to ventilations, as advocated by authorities in Great Britain; and (4) 100:2-CPR, 4 minutes of chest compressions only followed by CPR with a ratio of 100:2 compressions to ventilations. CPR was followed by standard advanced cardiac life support, 1 hour of critical care, and 24 hours of observation, followed by a neurologic evaluation. Results: There were no statistically significant differences in 24-hour survival among the 4 groups (standard CPR, 7/10; CC-CPR, 7/10; 50:5-CPR, 8/10; 100:2-CPR, 9/10). There were significant differences in 24-hour neurologic function, as evaluated by using the swine cerebral performance category scale. The animals receiving 100:2-CPR had significantly better neurologic function at 24 hours than the standard CPR group with a 15:2 ratio (1.5 versus 2.5; P=.007). The 100:2-CPR group also had better neurologic function than the CC-CPR group, which received chest compressions with no ventilations (1.5 versus 2.3; P=.027). Coronary perfusion pressures, aortic pressures, and myocardial and kidney blood flows were not significantly different among the groups. Coronary perfusion pressure as an integrated area under the curve was significantly better in the CC-CPR group than in the standard CPR group (P=.04). Minute ventilation and Pao₂ were significantly lower in the CC-CPR group. Conclusion: In this experimental model of bystander CPR, the group receiving compressions only for 4 minutes followed by a compression-ventilation ratio of 100:2 achieved better neurologic outcome than the group receiving standard CPR and CCCPR. Consideration of alternative chest compression-ventilation ratios might be appropriate.