Excessive chest compression rate is associated with insufficient compression depth in out-of-hospital cardic arrest

Introduction : In the 2010 Guidelines on Cardiopulmonary Resuscitation the relationship between compression rate and depth is considered to be a knowledge gap. In order to characterise this relationship, we performed an observational study in out-of-hospital cardiac arrest patients. We hypothesized that faster chest compressions are associated with decreased depth. Materials and methods : In patients undergoing out-of-hospital cardiopulmonary resuscitation according to 2005 Guidelines, chest compression rate and depth were recorded using an accelerometer on a Zoll E-series monitor-defibrillator providing feedback for compressions <4 cm deep and <80/min. Compression depth was compared for rates <80/min, 80-120/min and >120/min. Multilevel models with repeated measurements of compression depth and rate, nested within patients, were used with depth as a continuous and as a categorical variable. A difference in depth ≥0.5 cm was considered clinically significant. Results are reported as means and standard error. Results and discussion : One hundred and thirty-three consecutive patients were analysed (213409 compressions). Of all compressions 2% were <80/min, 62% between 80-120/min and 36% >120/min, 36 % were <4 cm deep, 45% between 4 and 5 cm, 19% >5cm. Compression depth for rates 80-120/min was 4.6 (±0.003) cm compared to 3.9 (±0.003) cm for compressions >120/min (mean difference 0.7 cm, P<0.001). In 77 out of 133 (58 %) patients a statistically significant lower depth was observed for rates >120/min compared to rates 80-120/min, in 40 out of 133 (30%) this difference was also clinically significant. Moreover, the multilevel models showed that the deepest compression occurred at a rate of 64/min, with progressively lower depths at higher rates. Age and sex of the patient had no additional effect on depth. Conclusions : This study showed an association between higher compression rates and lower compression depths. To avoid superficial compressions, feedback devices should alert rescuers when compression rates become excessively high.

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