Effect of Time of Day and EMS Performance Criteria on the Odds of Return of Spontaneous Circulation for Out-of-Hospital Cardiac Arrest

Introduction—Time of day might affect the expediency with which out-of-hospital cardiac arrest (OHCA) patients receive critical interventions. EMS professionals working extended shifts might be less likely to perform skills in a timely manner, and this delay in treatment might reduce the odds of achieving return of spontaneous circulation (ROSC) in the prehospital setting.

Objective—To analyze time-of-day variation in the likelihood of attaining ROSC.

Methods—A retrospective analysis of cardiac arrest patient records in the North Carolina Prehospital Medical Information System (PreMIS) database was conducted. Included were OHCAs occurring in adults between Jan. 1, 2012, and June 30, 2014. Excluded were traumatic arrests, unwitnessed arrests, arrests with on-scene termination of efforts, and records missing demographic or treatment variables. Time of day was stratified into morning (0700–1459), afternoon (1500–2259), and night (2300–0659) shifts. A logistic regression model for ROSC was fitted using time of day (referent=morning), demographic, and treatment variables as predictors.

Results—This study analyzed a total of 8,779 cardiac arrest patients, of whom 2,889 (32.9%) achieved ROSC in the field. The proportions of patients attaining ROSC were 33.8%, 35.2%, and 27.6% for morning, afternoon, and night respectively. In comparison to patients experiencing cardiac arrest during the morning hours, patients arresting at night were less likely to attain ROSC (OR 0.804, p=0.00) while arrests occurring during the afternoon were not statistically different from morning arrests (OR 0.939, p=0.26). Females (OR 1.33, p=0.00), patients with shockable presenting rhythms (OR 2.64, p=0.00), and patients receiving bystander CPR (OR 1.90, p=0.00) were more likely to attain ROSC. Each additional year of age (OR 0.996, p=0.00), unwitnessed arrests (OR 0.313, p=0.00), and each additional minute of EMS response time (OR 0.964, p=0.00) reduced the likelihood of ROSC.

Conclusion—Within the limitations of the study design, patients experiencing cardiac arrest at night were 20% less likely to attain ROSC after controlling for other confounding variables.