What is the maximal group size at which instructors are able to correct BLS course participants’ errors?

The ideal group size for effective teaching of cardiopulmonary resuscitation is currently under debate.

Medical students and nurses were recruited as simulated “BLS course participants”. Each was instructed to make three different errors randomly assigned from a list of 12 predefined errors during the seven-minute study period.

Eight different participating BLS instructors were randomized to one group size, ranging between three and ten simulated “BLS course participants”, which summed up to 64 participating instructors. Instructors were asked to correct all possibile errors.

The primary outcome was the maximal group size at which instructors were still able to correct 80% of BLS course participants’ errors.

The percentage of correctly identified and corrected errors varied between 89% for a group of three participants and 72% for a group of ten. Threshold of group size at which a life support instructor is still able to detect and correct 80% of participants’ errors during BLS training is six participants.

Fig. 1 – (A) Percentage of correctly identified and corrected errors (= success rate) for each group size. Coloured dots show the values of individual instructors as a function of group size. The black dots and vertical lines denote the median and interquartile range for each group. (B) Effect plot of the logistical-binomial regression model. The solid line depicts the mean prediction for a specific group size and the shaded bars denote the corresponding 95% confidence intervals of the prediction.

This randomized controlled simulation trial demonstrates that a BLS instructor is able to detect 80% of all errors made during CPR training when group size is limited to six or less participants. Logistic regression confirms a linear relationship between success rate of error detection and group size. A maximum instructor-to-participant ratio of one to six for cardiopulmonary resuscitation courses is recommended.

Nabecker S, Huwendiek S, Theiler L, Huber M, Petrowski K, Greif R. The effective group size for teaching cardiopulmonary resuscitation skills – A randomized controlled simulation trial. Resuscitation 2021. DOI: 10.1016/j.resuscitation.2021.05.034