Introduction: In telephone-assisted cardiopulmonary resuscitation (T-CPR), protocols are used to help the bystander via standardized instructions. However, the requested compression depth is rarely achieved. This study was designed to investigate the effect of intensified wording and/or repetitive target depth instructions on compression depth.

Methods: In this investigator-blinded, randomized, 4- armed, factorial study, 32 volunteers were requested to perform 10 minutes of compression only- CPR on a manikin. Participants were randomized either to standard wording (“push down 5cm”), intensified wording (“it is very important to push down 5cm every time”), standard wording with repeated instructions every 20 seconds, or intensified wording every 20 seconds. Three dispatchers were randomized to give the differing instructions. Primary outcome was defined as relative compression depth (absolute compression depth minus leaning depth) in millimeters. Secondary outcomes were physical exertion measured via heart rate, systolic/diastolic blood pressure, and the nine-hole peg test (NHPT) after CPR. We used a random effects regression model. Values are presented in mean and standard deviation or 95% Confidence interval as appropriate.

Results: Relative compression depth was 35±10 mm in the standard group versus 31±11 mm in the intensified wording group, versus 25±8 mm in the repeated standard and 31±14 mm in the repeated intensified wording group.  Adjusted for design, Body Mass Index and female sex, intensified wording and repetition led to decreased compression depth of 13 (95%CI: -25- -1) mm (p=0.04) and 9 (95%CI: -21-3) mm (p=0.13), respectively. Interaction was not statistically significant. Secondary outcomes showed no significant differences between standard and interventional groups.

Conclusion: For protocol driven, bystander T-CPR, we have demonstrated a significant negative effect of intensified wording, whereas repetition showed a non-significant negative effect.  Careful consideration of possible outcomes should occur before changing or intensifying the wording of CPR compression instructions.

Download Original Paper