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

AIM: 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. METHODS: 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 joules with anterior-lateral pad position. Primary outcome was survival to hospital discharge. RESULTS: 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 ohms [95% CI -12.9, -4.1]; p<0.001), and larger in per‑protocol analyses (AR -15.0 ohms [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 1,000 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. CONCLUSIONS: In this prematurely terminated RCT, MPA reduced transthoracic impedance but did not improve survival or other clinical outcomes in initially shockable OHCA. Trial registration ACTRN12621000804886.