Association of intensive care unit occupancy during admission and inpatient mortality: a retrospective cohort study

Purpose There is conflicting evidence regarding the influence of intensive care unit (ICU) occupancy at the time of admission on important patient outcomes such as mortality. The objective of this analysis was to characterize the association between ICU occupancy at the time of ICU admission and subsequent mortality. Methods This single-centre, retrospective cohort study included all patients admitted to the ICU at the Vancouver General Hospital between 4 January 2010 and 8 October 2017. Intensive care unit occupancy was defined as the number of ICU bed hours utilized in a day divided by the total amount of ICU bed hours available for that day. We constructed mixed-effects logistic regression models controlling for relevant covariates to assess the impact of admission occupancy quintiles on total inpatient (ICU and ward) and early (72-hr) ICU mortality. Results This analysis included 10,365 ICU admissions by 8,562 unique patients. Compared with ICU admissions in the median occupancy quintile, admissions in the highest and second highest occupancy quintile were associated with a significant increase in the odds of inpatient mortality (highest: odds ratio [OR], 1.33; 95% confidence interval [CI], 1.12 to 1.59; P value < 0.001; second highest: OR, 1.21; 95% CI, 1.02 to 1.44; P value < 0.03). No association between admission occupancy and 72-hr ICU mortality was observed. Conclusions Admission to the ICU on days of high occupancy was associated with increased inpatient mortality, but not with increased 72-hr ICU mortality. Capacity strain on the ICU may result in significant negative consequences for patients, but further research is needed to fully characterize the complex effects of capacity strain.