Time of admission to intensive care unit, strained capacity, and mortality: A retrospective cohort study

Abstract Purpose We sought to study the association between afterhours ICU admission and ICU mortality considering measures of strained ICU capacity. Materials and methods Retrospective analysis of 4141 admissions to 2 ICUs in Lisbon, Portugal (06/2016–06/2018). Primary exposure was ICU admission on 20:00 h–07:59 h. Primary outcome was ICU mortality. Measures of strained ICU capacity were: bed occupancy rate ≥ 90% and cluster of ICU admissions 2 h before or following index admission. Results There were 1581 (38.2%) afterhours ICU admissions. Median APACHE II score (19 vs. 20) was similar between patients admitted afterhours and others ( P  = .27). Patients admitted afterhours had higher crude ICU mortality (15.4% vs. 21.9%; P P  = .12). While bed occupancy rate ≥ 90% was more frequent in patients admitted afterhours (23.1% vs. 29.1%) or deceased in ICU (23.6% vs. 33.7%), cluster of ICU admissions was more frequent in patients admitted during daytime hours (75.2% vs. 58.9%) or that survived the ICU stay (70.1% vs. 63.9%; P  ≤ .001 for all). These measures of strained ICU capacity were not associated with adjusted ICU mortality ( P  ≥ .10 for both). Conclusions Afterhours ICU admission and measures of strained ICU capacity were associated with crude but not adjusted ICU mortality.