A randomised controlled trial of defibrillation with manual pressure augmentation during out-of-hospital cardiac arrest.

Abstract

To determine whether defibrillation with manual pressure augmentation (MPA) reduces transthoracic impedance and improves cardioversion and survival from initially shockable out-of-hospital cardiac arrest (OHCA) compared with standard defibrillation. Investigator-initiated, open-label, two-arm, cluster-randomised controlled trial across 216 ambulance stations in Victoria, Australia (April 1, 2022-January 31, 2023). Adults (≥18 years) with OHCA and a shockable rhythm receiving an attempted resuscitation were eligible. Intervention clusters applied MPA during shock delivery using a choreographed sequence and safety protocols; control clusters performed standard defibrillation. All shocks were biphasic at 200 J with anterior-lateral pad position. Primary outcome was survival to hospital discharge. The intention-to-treat (ITT) population included 560 patients, (intervention, n = 279; control, n = 281). Survival to hospital discharge was 39.8% (111/279) in the intervention group vs 39.9% (112/281) in the control (absolute risk difference [AR] -0.1% [95% CI -8.2%, 8.0%]; adjusted odds ratio [AOR] 1.00 [95% CI 0.71, 1.40]; p = 0.99). Twelve‑month survival, favourable neurologic outcome, and quality of life were similar between groups. Transthoracic impedance was significantly reduced with MPA (AR -8.5 O [95% CI -12.9, -4.1]; p < 0.001), and larger in per‑protocol analyses (AR -15.0 O [95% CI -22.8, -7.2]; p < 0.001). Compliance with MPA was low (23.6%). Perceptible shocks were uncommon and comparable across groups (0.75 vs 0.71 per 1000 shocks delivered); no serious injuries occurred. The trial was prematurely terminated due to external safety reviews and operational delays, without outcome unblinding at the time of termination. In this prematurely terminated RCT, MPA reduced transthoracic impedance but did not improve survival or other clinical outcomes in initially shockable OHCA. ACTRN12621000804886.