Effect of vertical location on survival outcomes for out-of-hospital cardiac arrest in Singapore

Background: A large proportion of out-of-hospital cardiac arrest (OHCA) cases occur in high-rise residential buildings. This study aims to investigate the effect of vertical location on survival outcomes and response times. Methods: This is a retrospective study based on data obtained from the Singapore cohort of the Pan-Asian Resuscitation Outcomes Study (PAROS) from January 2011 to December 2014. Study subjects were OHCA cases, unwitnessed and transported by EMS personnel, with known vertical location (floor) data. Traumatic arrests with no resuscitation attempted and missing vertical locations were excluded. The primary outcome was survival to hospital discharge or 30 days post-cardiac arrest. Results: A total of 5678 OHCA cases were included in the study. The effect of floors on survival was manifested as a U-shaped response. Survival rates of 4.5% for the 4 pooled basement floors and 6.2% for the ground floor (floor 1) were contrasted by a substantial drop to 2.7% at floor 2 and continuing decline to 0.7% at floor 6. In a multivariable model using stepwise logistic regression, both linear (p = 0.0285) and quadratic (p = 0.0018) floor effects remained significant after adjustment for other significant risk factors, age, bystander witnessed arrest, first arrest rhythm, ROSC on scene/enroute, and EMS response times. Harrell's C-statistic for a predictive model incorporating these variables was 0.933. Conclusions: Vertical location is associated with OHCA survival probability with a U-shaped response, and this significance remained after adjustment for other significant OHCA variables. This relationship is likely multifactorial and more research is needed to elucidate the various factors.