Association between hourly call volume in the emergency medical dispatch center and dispatcher-assisted cardiopulmonary resuscitation instruction time in out-of-hospital cardiac arrest

Cardiac arrest recognition, ambulance dispatch and dispatcher-assisted cardiopulmonary resuscitation (DA-CPR) by emergency medical dispatch (EMD) are crucial for an optimal outcome of out-of-hospital cardiac arrest (OHCA). In EMD, crowding is caused by a mismatch between the number of emergency calls and the number of dispatchers available per shift. Crowding in the emergency department has been shown to decrease performance and outcomes; however, little is known about the effect of crowding in EMD. We aimed to evaluate the incidence of crowding in the EMD and the effect of emergency call crowding on dispatcher-assisted CPR instruction performance in OHCA calls. We used a nationwide OHCA database from 2013 to 2016 consisting of patients with the presumed cardiac origin who were dispatched by Seoul EMD. The main exposure was an hourly number of total incoming emergency calls to EMD. The number of hourly calls was categorized into quartiles (≤40 calls, 41–51 calls, 52–61 calls and ≥62 calls). The primary outcome was successful DA-CPR instruction provision within 120 s. Adjusted odds ratios (AORs) and 95% confidence intervals (CIs) were estimated to evaluate the association between EMD crowding and outcomes in the multivariable logistic regression model. Of a total of 12,722 patients, the proportion of successful DA instruction was highest in the least-crowded quartile and lowest in the most-crowded quartile (22.7% vs. 15.0%, p