In-Hospital vs. Out-of-Hospital Cardiac Arrest: Patient Characteristics and Survival

Background Cardiac arrests are often categorized into two separate groups depending on the location of the arrest: in-hospital cardiac arrest (IHCA) and out-of-hospital cardiac arrest (OHCA). Despite this distinction, few studies have compared the two groups directly. The aim of this study was to compare patient characteristics, cardiac arrest characteristics, and outcomes for IHCA and OHCA patients. Methods Data on IHCA and OHCA in Denmark were obtained from two nationwide, prospective registries. All adult (≥18 years old) patients with index IHCA or OHCA from January 1, 2017 to December 31, 2018 were included. Supplementary information on outcomes, hospitalizations, and chronic diseases came from additional national registries. The primary outcome was 30-day survival and secondary outcomes were return of spontaneous circulation (ROSC) and 1-year survival. Results The study included 3501 patients with IHCA and 8846 patients with OHCA. The two groups were similar in demographics, most comorbidities, and initial cardiac arrest rhythm. In the unadjusted analysis, IHCA was associated with increased survival to 30 days compared to OHCA (risk ratio [RR] = 1.41; 95% CI, 1.30; 1.54) and 1 year (RR = 1.46; 95% CI, 1.33; 1.61). Adjusting for age, sex, and comorbidities did not change the RR substantially. When cardiac arrest characteristics were added to the model, the RR decreased from 1.51 (95% CI, 1.39; 1.65) to 1.06 (95% CI, 0.93; 1.20) for survival to 30 days and from 1.66 (95% CI, 1.50; 1.84) to 1.09 (95% CI, 0.94; 1.26) for survival to 1 year. In all subgroup analyses based on cardiac arrest characteristics (e.g. witnessed status), the association between location and outcome was substantially mitigated compared to the primary analyses. Conclusions In this large, national study, we found that IHCA and OHCA patients were remarkably similar in demographics and most comorbidities. IHCA patients had better outcomes compared to OHCA patients, although these differences disappeared when comparing patients with similar cardiac arrest characteristics.