Background: The 2005 revised guidelines for cardiopulmonary resuscitation (CPR) suggest a universal compression-to-ventilation (C:V) ratio of 30:2. The effects of this ratio in a realistic CPR scenario have not been investigated completely.
Material and methods: After 4 min of untreated ventricular fibrillation (VF), 24 pigs were randomly assigned to 6 min of basic-life support (BLS) CPR with 21% oxygen, and either (1) chest compressions only ("CC" group, n=8), or (2) cycles of 30 compressions followed by two breaths with a self-inflating bag (Fio2 0.21, C:V ratio 30:2; "30:2" group, n=8), or (3) 15 compressions followed by two breaths (C:V ratio 15:2; "15:2" group, n=8), all followed by advanced life support.
Results: Arterial PO2 during BLS-CPR was higher in the 15:2 group compared to the 30:2 and CC groups (74+/-3 vs. 59+/-2 and 33+/-4 mmHg, respectively; p<0.05). Both mixed-venous PO2 and SO2 were higher in the 15:2 and 30:2 groups, compared to the CC group ( PO2 : 23+/-2 and 25+/-1 vs. 17+/-1 mmHg; SO2: 21+/-6 and 19+/-3 vs. 8+/-1 %, respectively; p<0.05). Arterial pH decreased in the 30:2 and CC groups compared to the 15:2 group (7.33+/-0.03 and 7.25+/-0.02 vs. 7.51+/-0.04, respectively; p<0.001). 4/8, 2/8, and 0/8 animals in the 15:2, 30:2, and CC groups, respectively, had ROSC at the end of the study period (p=ns).
Conclusions: Increasing the chest compression ratio from 15:2 to 30:2 resulted in changes in arterial, but not mixed-venous, blood gases; therefore, the advantages of more chest compressions may outweigh a decrease in gas exchange.