Ambulance Density and Outcomes After Out-of-Hospital Cardiac Arrest.

Background: In out-of-hospital cardiac arrest (OHCA), geographic disparities in outcomes may reflect baseline variations in patients' characteristics but may also result from differences in the number of ambulances providing basic life support (BLS) and advanced life support (ALS). We aimed at assessing the association between allocated ambulance resources and outcomes in OHCA patients in a large urban community.

Methods: From May 2011 to January 2016, we analyzed a prospectively collected Utstein database for all OHCA adults. Cases were geocoded according to 19 neighborhoods and the number of BLS (firefighters performing cardiopulmonary resuscitation and applying automated external defibrillator) and ALS ambulances (medicalized team providing advanced care such as drugs and endotracheal intubation) was collected. We assessed the respective associations of Utstein parameters, socioeconomic characteristics, and ambulance resources of these neighborhoods using a mixed-effect model with successful return of spontaneous circulation as the primary end point and survival at hospital discharge as a secondary end point.

Results: During the study period, 8754 nontraumatic OHCA occurred in the Greater Paris area. Overall return of spontaneous circulation rate was 3675 of 8754 (41.9%) and survival rate at hospital discharge was 788 of 8754 (9%), ranging from 33% to 51.1% and from 4.4% to 14.5% respectively, according to neighborhoods ( P<0.001). Patient and socio-demographic characteristics significantly differed between neighborhoods ( P for trend <0.001). After adjustment, a higher density of ambulances was associated with successful return of spontaneous circulation (respectively adjusted odds-ratio [aOR], 1.31 [1.14-1.51]; P<0.001 for ALS ambulances >1.5 per neighborhood and aOR, 1.21 [1.04-1.41]; P=0.01 for BLS ambulances >4 per neighborhood). Regarding survival at discharge, only the number of ALS ambulances >1.5 per neighborhood was significant (aOR, 1.30 [1.06-1.59] P=0.01).

Conclusions: In this large urban population-based study of out-of-hospital cardiac arrests patients, we observed that allocated resources of emergency medical service are associated with outcome, suggesting that improving healthcare organization may attenuate disparities in prognosis.