Wildfire-related PM₂.₅ and Intensive Care Unit Admissions and Bed Utilization in the United States, 2006-2015

Abstract

BACKGROUND AND AIM: Wildfire smoke is a growing public health concern in the United States. Numerous studies have documented associations between ambient smoke exposure and severe patient outcomes for single fire seasons or limited geographic regions. However, there are few national-scale health studies of wildfire smoke in the U.S., few studies investigating Intensive Care Unit (ICU) admissions as an outcome, and few specifically framed around hospital operations. This study retrospectively examined the associations between ambient wildfire-related PM₂.₅ at a hospital ZIP code with total hospital ICU admissions using a national-scale hospitalization data set during the years 2006-2015. METHODS: Wildfire smoke was characterized using a combination of kriged PM₂.₅ monitor observations and satellite-derived plume polygons from NOAA’s Hazard Mapping System. ICU admissions data were acquired from Premier, Inc. and encompass 15-20% of all U.S. ICU admissions during the study period. Associations were estimated using a distributed-lag conditional Poisson model under a time-stratified case-crossover design. The impact on ICU admissions and bed utilization of a severe 7-day 120 μg/m³ smoke wave was simulated. RESULTS:We found that a 10 μg/m³ increase in daily wildfire PM₂.₅ was associated with a 2.7% (95% CI: 1.3, 4.1; p=0.00018) increase in ICU admissions five days later. Following the simulated smoke wave, our results predict ICU bed utilization peaking at 131% (95% CI: 43, 239; p0.00001) over baseline. CONCLUSIONS:Our work suggests that hospitals may need to pre-position vital critical care resources when severe smoke events are forecast. KEYWORDS: Intensive Care Unit, Wildfire, Smoke, Particulate Matter, Critical Care