Association Between Intensive Care Unit Occupancy at Discharge, Afterhours Discharges, & Clinical Outcomes: An Historical Cohort Study

Background: There is a paucity of contemporary, patient-level data evaluating the association between discharge occupancy in the intensive care unit (ICU) and clinical outcomes such as readmission and mortality. Additionally, it is unknown whether increased occupancy at discharge may modify the timing of discharge (i.e. increased afterhours discharge) and further provoke negative clinical consequences. The objective of this single-center historical cohort study was to explore the association between ICU occupancy on the day of discharge and afterhours discharges, 72-hour readmission and 30-day mortality. Methods: This was a historical cohort study of a single large quaternary ICU in Canada. Discharge occupancy was defined as the number of hours of patient care delivered on the day of discharge divided by the total amount of hours of care available for that day (number of funded beds x 24 hours). Afterhours discharge was defined as a discharge between 22:00 and 6:59. Logistic regression models controlling for important covariates were constructed. Adjusted restricted cubic spline models were also created to control for non-linear relationships. Results: A total of 8,862 ICU discharges, representing 7,288 individual patients, between April 1, 2010 and August 10, 2017 were included in this analysis. A total of 1180 (13.3%) afterhours discharges, 408 (4.6%) 72-hour readmissions, and 574 (6.5%) 30-day post discharge deaths occurred. In the adjusted analysis, greater discharge occupancy was associated with afterhours discharges (per 10% increase; adjusted odds ratio (aOR) 1.12, 95% 1.03-120, p = 0.005). Discharge occupancy was not associated with 72-hour readmission (per 10% increase; aOR 0.97, 95% CI 0.87-1.09, p= 0.624) or 30-day mortality (per 10% increase; aOR 1.05, 95% CI 0.95-1.16, p= 0.323). Afterhours discharge was not associated with neither 72-hour readmission (aOR 1.15, 95% CI 0.86-1.54, p= 0.341) nor 30-day mortality (aOR 1.05, 95% CI 0.82-1.36, p= 0.691). Conclusions: Greater ICU occupancy on the day of discharge was associated with a significant increase in afterhours discharges. However, neither discharge occupancy nor afterhours discharge were associated with 72-hr readmission or 30-day mortality. Keywords: Intensive care unit; occupancy; capacity strain; process-of-care; afterhours discharge; readmission; mortality