Factors associated with CPR quality in out-of-hospital cardiac arrest

Although high quality cardiopulmonary resuscitation (CPR) has been associated with increased survival from out-of-hospital cardiac arrest (OHCA), little is known about arrest factors that influence CPR quality, particularly with trained rescuers. This study examined the association between CPR quality and arrest factors in OHCA.

A retrospective observational study using data from the Victorian Ambulance Cardiac Arrest Registry (VACAR) between 11-February-2019 and 31-May-2025. The study included all adult, medical OHCAs with an attempted resuscitation involving >2  min of CPR. Multivariable fractional, logistic and linear regression models were used to assess the factors associated with percentage of compressions at target depth (50-100  mm), percentage at target rate (100-120/min), compression fraction ≥90 % and mean release velocity.

Among 9174 OHCAs examined, median [Q1, Q3] percentage of compressions at target depth was 81 % [58, 93], rate 68 % [48, 82], compression fraction 92 % [89, 94] and mean (standard deviation) release velocity was 380 (65) mm/s. In multivariable models, Fire Services assistance and longer resuscitation duration were associated with improvements across all metrics, while increased number of rescuers improved depth and release velocity. Reduced CPR performance was associated with residential care home location, increasing patient age (depth and compression fraction), shockable arrest rhythm and EMS-witnessed arrest (compression fraction) and metropolitan arrest location.

This study identified prehospital factors associated with improved CPR quality, including the involvement of fire-fighter first responders, highlighting their vital role in the emergency medical response. Recognising areas of poorer performance, such as in residential care and shockable arrest rhythms, can inform targeted improvements.