Did COVID-19 ICU patient mortality risk increase as Colorado hospitals filled? A retrospective cohort study

Abstract

Objectives To assess whether increasing levels of hospital stress—measured by intensive care unit (ICU) bed occupancy (primary), ventilators in use and emergency department (ED) overflow—were associated with decreasing COVID-19 ICU patient survival in Colorado ICUs during the pre-Delta, Delta and Omicron variant eras.Design A retrospective cohort study using discrete-time survival models, fit with generalised estimating equations.Setting 34 hospital systems in Colorado, USA, with the highest patient volume ICUs during the COVID-19 pandemic.Participants 9196 non-paediatric SARS-CoV-2 patients in Colorado hospitals admitted once to an ICU between 1 August 2020 and 1 March 2022 and followed for 28 days.Outcome measures Death or discharge to hospice.Results For Delta-era COVID-19 ICU patients in Colorado, the odds of death were estimated to be 26% greater for patients exposed every day of their ICU admission to a facility experiencing its all-era 75th percentile ICU fullness or above, versus patients exposed for none of their days (OR: 1.26; 95% CI: 1.04 to 1.54; p=0.0102), adjusting for age, sex, length of ICU stay, vaccination status and hospital quality rating. For both Delta-era and Omicron-era patients, we also detected significantly increased mortality hazard associated with high ventilator utilisation rates and (in a subset of facilities) states of ED overflow. For pre-Delta-era patients, we estimated relatively null or even protective effects for the same fullness exposures, something which provides a meaningful contrast to previous studies that found increased hazards but were limited to pre-Delta study windows.Conclusions Overall, and especially during the Delta era (when most Colorado facilities were at their fullest), increasing exposure to a fuller hospital was associated with an increasing mortality hazard for COVID-19 ICU patients.