Association between time of admission to the ICU and mortality: a systematic review and metaanalysis

The organizational and staffing structure of an ICU influences the outcome of critically ill and injured patients. A change in the ICU staffing structure frequently occurs at nighttime and on weekends (off-hours). We postulated that patients who are admitted to an ICU during off hours may be at an increased risk of death.

We performed a systematic review of the literature to assess whether admission to an ICU during off-hours is associated with an increased mortality. We selected studies that evaluated the association between time of admission to the ICU and mortality, with adjustment for severity of disease. We excluded studies that included pediatric and non-ICU patients. Study characteristics extracted included date of publication, study design, country where study was done, study population, time factor (weekend or night shift), severity adjustment tool, and outcome.

Ten cohort studies met our inclusion criteria; eight of these studies evaluated nighttime admissions, whereas six studies evaluated weekend admissions. The pooled analysis demonstrated that nighttime admission was not associated with an increased mortality (odds ratio [OR], 1.0 [95% CI, 0.87-1.17]; P = .956); however, patients admitted over the weekend had a significant increase in the adjusted risk of death (OR, 1.08 [95% CI, 1.04-1.13]; P < .001). Significant heterogeneity was found in the studies that evaluated nighttime admissions.

Whereas patients admitted to an ICU over the weekend appear to be at an increased risk of death, nighttime admissions were not associated with an increased mortality. The lower level of staffing and intensity of care provided by many hospitals over the weekend may account for this finding. The heterogeneity noted between studies evaluating nighttime admissions likely reflects the diverse organizational structure of the hospitals and ICUs where these studies were carried out.