Distribution of clinically identified reversible causes in emergency department and out-of-hospital cardiac arrest: a retrospective cohort study.

BACKGROUND: Rapid identification of potentially reversible causes is essential during cardiac arrest resuscitation. The American Heart Association 5Hs and 5Ts framework is widely used as a structured cognitive aid during resuscitation. Emergency department cardiac arrest (EDCA) occurs in a distinct clinical environment and may involve different patterns of clinically identified reversible causes than out-of-hospital cardiac arrest (OHCA). We aimed to compare the distribution of clinically identified reversible causes between EDCA and OHCA. METHODS: We conducted a retrospective cohort study of adult cardiac arrest patients who received cardiopulmonary resuscitation in a tertiary emergency department between 2018 and 2024. Patients were classified as EDCA or OHCA. Reversible causes were classified using predefined operational definitions based on contemporaneous clinical documentation and available diagnostic information during resuscitation, representing clinically identified or suspected reversible causes rather than definitive etiologic diagnoses. The primary analysis compared the distribution of clinically identified reversible causes between EDCA and OHCA. Secondary exploratory analyses used Firth's penalized logistic regression with prespecified confounding adjustment. RESULTS: Among 910 patients, 275 (30.2%) had EDCA and 635 (69.8%) had OHCA. Hypoxia was the most frequently identified cause but occurred less often in EDCA (46.6% vs. 57.2%; adjusted odds ratio [aOR], 0.61; 95% CI, 0.45-0.83). Hypovolemia was identified more frequently in EDCA (33.1% vs. 23.2%; aOR 1.80, 95% CI 1.22-2.65). Cardiac tamponade was also identified more frequently in EDCA (2.9% vs. 0.6%; aOR 5.14, 95% CI 1.52-17.40). No statistically significant adjusted differences were observed for the remaining reversible causes. CONCLUSION: Among patients receiving cardiopulmonary resuscitation in the emergency department, the distribution of clinically identified reversible causes differed between EDCA and OHCA. Hypovolemia and cardiac tamponade were identified more frequently in EDCA, whereas hypoxia was identified less frequently. These findings describe patterns of clinical recognition during resuscitation rather than definitive etiologic differences and should be confirmed in multicenter studies using standardized disease-based etiologic classifications.