1828: DUTY CYCLE OF 33% IS ASSOCIATED WITH HIGHER END-TIDAL CO2 LEVEL DURING CARDIOPULMONARY RESUSCITATION

Abstract

Learning Objectives: The aim of this crossover experimental study was to investigate whether a duty cycle of 33% is associated with higher end-tidal CO2 (ETCO2) level during cardiopulmonary resuscitation (CPR) compared with a duty cycle of 50%. Methods: Six male domestic pigs were assigned to the ‘DC33’ group (n = 3) or an ‘DC50’ group (n = 3) after experiments using hemorrhage-autotransfusion model. After 3 min of no-flow time from induced cardiac arrest, 5 min of chest compression with a rate of 100 per min was provided with a duty cycle of 33% for the DC33 group and 50% for the DC50 group (phase I), then 1 mg of epinephrine was administered intravenously, and defibrillation was delivered every minute until return of spontaneous circulation (ROSC). After 30 min of stabilization period from ROSC, the pigs were re-assigned to the opposite groups. Cardiac arrest was induced once again, and 5 min of chest compression was provided after 3 min from the induction of cardiac arrest in the same manner as in the phase I (phase II). The primary outcome was ETCO2 and the secondary outcomes were arterial systolic blood pressure (ASBP) and coronary perfusion pressure (CPP). Results: ETCO2 (20.5 ± 4.5 mmHg vs 19.8 ± 5.5 mmHg, P = 0.005), ASBP (77.8 ± 19.5 vs 71.8 ± 10.9, P < 0.001), and CPP (15.0 ± 13.8 vs 8.0 ± 13.9, P < 0.001) during 5 min of chest compression were all higher in the DC33 group compared with the DC50 group. In a linear mixed model, duty cycle of 33% affected ETCO2 significantly (P < 0.001), increasing ETCO2 in the DC33 group by 0.88 ± 0.18 mmHg compared with DC50 group. The interaction between ETCO2 and time was significant (P < 0.001), and ETCO2 increased over time in the DC33 group (0.53 mmHg/min) while ETCO2 decreased in the DC50 group (-0.89 mmHg/min). Duty cycle of 33% increased ASBP (6.25 mmHg, P < 0.001) and CPP (8.34 mmHg, P < 0.001) compared with duty cycle of 50%. The interactions were also significant between ASBP and time (2.00 mmHg/min in DC33 group vs -0.88 mmHg/min in DC50 group, P < 0.001) and between CPP and time (0.89 mmHg/min in DC33 group vs -2.62 mmHg in DC50 group, P < 0.001). Conclusions: A duty cycle of 33% increased ETCO2 during CPR compared with a duty cycle of 50%. Moreover, ETCO2 increased over time during CPR with a duty cycle of 33% while ETCO2 decreased with a duty cycle of 50%.