Purpose: Retention of skills and knowledge has been shown to be poor after resuscitation training. The effect of a "booster" is controversial and may depend on its timing. We compared the effectiveness of an early versus late booster session after Basic Life Support (BLS) training for skill retention at 4 months.

Methods: We performed a single-blind randomized controlled trial in a simulation environment. Eligible participants were adult laypeople with no BLS training or practice in the 6 months prior to the study. We provided participants with formal BLS training followed by an immediate BLS skills post-test. We then randomized participants to one of three groups: control, early booster, or late booster. Based on their group allocation, participants attended a brief BLS refresher at either 3 weeks after training (early booster), at 2 months after training (late booster), or not at all (control). All participants underwent a BLS skills retention test at 4 months. We measured BLS skill performance according to the Heart and Stroke Foundation's skills testing checklist for adult CPR and the use of an automated external defibrillator.

Results: A total of 80 laypeople were included in the analysis (control group, n = 28; early booster group, n = 23; late booster group, n = 29). The late booster group achieved better skill retention (mean difference in checklist score at retention compared to the immediate post-test = - 0.8 points out of 15, [95% CI - 1.7, 0.2], P = 0.10) compared to the early booster (- 1.3, [- 2.6, 0.0], P = 0.046) and control group (- 3.2, [- 4.7, - 1.8], P < 0.001).

Conclusion: A late booster session improves BLS skill retention at 4 months in laypeople.

Trial registration number: NCT02998723.