Duty cycle of 33% increases cardiac output during cardiopulmonary resuscitation

BACKGROUND: The aim of this study was to investigate whether 33% duty cycle increases end-tidal carbon dioxide (ETCO(2)) level, a surrogate measurement for cardiac output during cardiopulmonary resuscitation (CPR), compared with 50% duty cycle. METHODS: Six pigs were randomly assigned to the DC33 or DC50 group. After 3 min of induced ventricular fibrillation (VF), CPR was performed for 5 min with 33% duty cycle (DC33 group) or with 50% duty cycle (DC50 group) (phase I). Defibrillation was delivered until return of spontaneous circulation (ROSC) thereafter. After 30 min of stabilization, the animals were re-assigned to the opposite groups. VF was induced again, and CPR was performed (phase II). The primary outcome was ETCO(2) during CPR, and the secondary outcomes were coronary perfusion pressure (CPP), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and right atrial pressure (RAP). RESULTS: Mean ETCO(2) was higher in the DC33 group compared with the DC50 group (22.5 mmHg vs 21.5 mmHg, P = 0.018). In a linear mixed model, 33% duty cycle increased ETCO(2) by 1.0 mmHg compared with 50% duty cycle (P < 0.001). ETCO(2) increased over time in the DC33 group [0.6 mmHg/min] while ETCO(2) decreased in the DC50 group [-0.6 mmHg/min] (P < 0.001). Duty cycle of 33% increased SAP (6.0 mmHg, P < 0.001), DAP (8.9 mmHg, P < 0.001) RAP (2.6 mmHg, P < 0.001) and CPP (4.7 mmHg, P < 0.001) compared with the duty cycle of 50%. CONCLUSION: Duty cycle of 33% increased ETCO(2), a surrogate measurement for cardiac output during CPR, compared with duty cycle of 50%. Moreover, ETCO(2) increased over time during CPR with 33% duty cycle while ETCO(2) decreased with 50% duty cycle.