Observed long-term mortality after 18,000 person-years among survivors in a large regional drowning registry

Abstract

Aim: Long-term outcomes beyond one year after non-fatal drowning are uncharacterized. We estimated long-term mortality and identified prognostic factors in a large, population-based cohort.

Methods: Population-based prospective cohort study (1974-1996) of Western Washington Drowning Registry (WWDR) subjects surviving the index drowning through hospital discharge. Primary outcome was all-cause mortality through 2012. We tabulated Utstein-style exposure variables, estimated Kaplan-Meier curves, and identified prognostic factors with Cox proportional hazard modeling. We also compared 5-, 10-, and 15-year mortality estimates of the primary cohort to age-specific mortality estimates from United States Life Tables.

Results: Of 2824 WWDR cases, 776 subjects (5[IQR 2-17] years, 68% male) were included. Only 63 (8%) non-fatal drowning subjects died during 18,331 person-years of follow-up. Long-term mortality differed by Utstein variables (age, precipitating alcohol use, submersion interval, GCS, CPR, intubation, defibrillation, initial vital signs, neurologic status at hospital discharge) and inpatient markers of illness severity (mechanical ventilation, vasopressor use, seizure, pneumothorax). Survival differed by age (HR 1.04;95%CI 1.03-1.05), drowning-related cardiac arrest (HR 3.47;95%CI 1.97-6.13), and neurologic impairment at hospital discharge (HR 5.10;95% CI 2.70-9.62). In adjusted analysis, age (HR 1.05;95%CI 1.03-1.06) and severe neurologic impairment at discharge (HR 2.31;95%CI 1.01-5.28) were associated with long-term mortality. Subjects aged 5-15 years had higher mortality risks than those calculated from Life Tables.

Conclusion: Most drownings were fatal, but survivors of non-fatal drowning had low risk of subsequent long-term mortality similar to the general population that was independently associated with age and neurologic status at hospital discharge.

Keywords: Drowning; Long-term follow-up; Mortality; National Death Index.