Pre-hospital factors and survival after out-of-hospital cardiac arrest according to population density, a nationwide study

Aim: This study aimed to examine the impact of population density on bystander cardiopulmonary resuscitation (CPR) and survival after out-of-hospital cardiac arrest (OHCA). Methods: Through the Danish Cardiac Arrest Registry (2001-2013), OHCAs -18 years of presumed cardiac cause were identified, and divided according to the OHCA location in four population density groups (inhabitants/km(2)) based on urban/rural area-definitions: low (<300/km(2)), medium (300 -1499/km2), high (1500-2999/km(2)), very high (>3000/km(2)). The association between population density, bystander cardiopulmonary resuscitation (CPR) and survival was examined using logistic regression, adjusted for age, sex, comorbitidies and calendar-year. Results: 18,248 OHCAs were identified. Patients in areas of high compared to low population density were older, more often female, had more comorbidities, more witnessed arrests (very high: 59.6% versus low: 55.0%), shorter response time (very high: 10min versus low: 14min), but less bystander CPR (very high: 34.3% versus low: 45.1%). Thirty-day survival was higher in areas of higher population density (very high: 10.2% vs. low 5.3%), also in best-cases of witnessed arrests with bystander CPR and response time <10min (very high: 33.6% versus low: 13.8%). The same trends were found in adjusted analyses with lower odds for bystander CPR (odds ratio [OR] 0.55 95% confidence interval [CI] 0.46-0.66) and higher odds for 30-day survival (OR 2.78, 95%CI 1.95-3.96) in the highest population density areas compared to low. Conclusions: Having an OHCA in higher populated areas were found associated with less bystander CPR, but higher survival. Identification of arearelated factors can help target future pre-hospital care.