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

AimTo determine whether defibrillation with manual pressure augmentation (MPA) reduces transthoracic impedance and improves cardioversion and survival from initially shockable outof-hospital cardiac arrest (OHCA) compared with standard defibrillation. MethodsInvestigator-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. ResultsThe 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. ConclusionsIn this prematurely terminated RCT, MPA reduced transthoracic impedance but did not improve survival or other clinical outcomes in initially shockable OHCA.