DOES HYPOXIA OR HYPERCARBIA INDEPENDENTLY AFFECT RESUSCITATION FROM CARDIAC-ARREST

Study objective: In a previous cardiopulmonary resuscitation (CPR) study in swine, ventilation was associated with improved rate of return of spontaneous circulation (ROSC) compared with nonventilated animals, which had greater hypoxia and hypercarbic acidosis. We used the same model to determine the independent effect of hn?olria and hypercarbic acidosis on ROSC after cardiac arrest. Design: Laboratory model of cardiac arrest. Setting: University teaching hospital laboratory. Participants: Domestic swine (23 to 61 kg). Interventions: Twenty-four swine were randomly assigned to three groups receiving ventilation during CPR with 85% O-2/15% N-2 (control), 95% O-2/5% CO2 (hypercarbia), or 10% O-2/90% N-2 (hypoxia). Ah animals had ventricular fibrillation for 6 min without CPR, then CPR with one of the ventilation gases for 10 min,then defibrillation. Animals without ROSC received epinephrine, 85% O-2, CPR for another 3 min, and defibrillation. Measurements and results: During the tenth minute of CPR, the hypercarbic group had more mean (SD) arterial hypercarbia than the control group (PCO2, 47+/-6, compared with 34+/-6; p<0.01), and greater mixed venous hypercarbia (PCO2, 72+/-14, compared with 59+/-8; p<0.05), while mean arterial and mixed venous Pot was not significantly different. The hypoxic group had significantly less mean arterial (43+/-9 compared with 228+/-103 mm Hg) and mixed venous (22+/-5 compared with 35+/-7 mm Hg) Po-2 when compared with the control group (p<0.01), white mean arterial and mixed venous PCO2 were not signiticantly different. Thus, the model succeeded in producing isolated hypercarbia without hypoxia in the hypercarbic group and isolated hypoxia without hypercarbia in the hypoxic group, The rate of ROSC was 6/8 (75%) for the control group, 1/8 (13%) for the hypercarbic group, and 1/8 (13%) for the hypoxic group (p<0.02). Conclusions: Both hypoxia and hypercarbia independently had an adverse effect on resuscitation from cardiac arrest. In this model with a prolonged interval of untreated cardiac arrest, adequate ventilation was important for resuscitation.