Positive association between ambulance double-crewing and OHCA outcomes: A New Zealand observational study

Background and objectives: New Zealand emergency medical service (EMS) crewing configurations generally place one (single) or two (double) crew on each responding ambulance unit. Recent studies demonstrated that double-crewing was associated with improved survival from out-of-hospital cardiac arrest (OHCA), therefore single-crewed ambulances have been phased out. We aimed to determine the association between this crewing policy change and OHCA outcomes in New Zealand. Methods: This is a retrospective observational study using data from the St John OHCA Registry on patients treated during two dierent time periods: the Pre-Period (1 October 2013-30 June 2015), when single-crewed ambulances were in use by EMS, and the Post-Period (1 July 2016-30 June 2018) when single-crewed ambulances were being phased out. Geographic areas identified as having low levels of double crewing during the Pre-Period were selected for investigation. The outcome of survival to thirty-days post-OHCA was investigated using logistic regression analysis. Results: The proportion of double-crewed ambulances arriving at OHCA events increased in the Post-Period (81.8%) compared to the Pre-Period (67.5%) (p <= 0.001). Response times decreased by two minutes (Pre-Period: median 8 min, IQR [6-11], Post-Period: median 6 min, IQR [4-9]; p <= 0.001). Thirty-day survival was significantly improved in the Post-Period (OR 1.63, 95%CI (1.04-2.55), p = 0.03). Conclusions: An association between improved OHCA survival following increased responses by double-crewed ambulances was demonstrated. This study suggests that improvements in resourcing are associated with improved OHCA outcomes.