(Not) Everybody Is Working for the Weekend*

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The intensity of intensivist staffing in the ICU has been known to be an important influence on ICU outcomes for many years (1). In the United States, requirements for certification by organizations such as the Leapfrog Group, specifying intensivist presence during daytime hours, are potentially at odds with a putative shortage of intensivists and models of care required to address the needs of a burgeoning critical care patient population (2–4). Although the ICU may be staffed on weekends with highly skilled nurses and respiratory therapists, lessened intensivist availability during that time has led to concerns about care delivery and outcomes.
Epidemiologic clues about suboptimal medical care on the weekends have been present since the 1970s. Rogot et al (5) published the daily variations in congestive heart disease, stroke and influenza mortality which clearly demonstrated higher rates of death on weekends compared with weekdays, the so-called “weekend effect.” It was unclear from this initial observational study whether increased mortality was the result of increased disease prevalence, severity, or suboptimal care. That question was addressed in a study by Bell and Redelmeier (6) which evaluated a cohort of over 3 million hospital admissions from 1988 to 1997. The authors demonstrated that conditions such as ruptured abdominal aortic aneurysm, acute epiglottis, and pulmonary embolism had an increased mortality when a patient was admitted over the weekend. Furthermore, of the top 100 conditions that resulted in hospital mortality, 23 demonstrated this alarming pattern of higher weekend mortality.
Since 2001, over 17 cohort studies have focused on the question of whether out-of-hours ICU admission is associated without worsened outcomes. These studies have been highly variable, and discrepancies between studies have been attributed to different work shift schemes, intensivist coverage, physician-to-patient ratio, and even definition of “out-of-hours.” Previously, the most complete analysis was done by Cavallazzi et al (7) in a meta-analysis of 10 cohort studies consisting of a total of over 135,000 patients. Contrary to expectations, there was no association between night admission and worsened outcomes; however, an association between weekend admissions and mortality was found. This latter finding was met with skepticism as it was mainly driven by results from only one of the 10 studies included in the analysis. Another shortcoming of the systematic review by Cavallazzi et al (7) was the lack of consideration of potential causes for the increased weekend mortality.
Subsequently, in the years since 2010, at least seven studies have been published which appeared to confirm the weekend effect. In this issue of Critical Care Medicine, Galloway et al (8) present an updated systematic review regarding the impact of out-of-hours admission on mortality. An analysis of 902,551 patients from 16 cohort studies conducted across multiple countries was conducted in order to identify whether time of admission or day of admission was associated with increased ICU mortality. Consistent with Cavallazzi et al (7), nighttime admissions were not at an increased risk of death, but a significant increase in mortality for patients admitted over the weekend (odds ratio [OR], 1.05; 95% CI, 1.01–1.09) was found. Additionally, the authors sought to determine which factors contributed to increased weekend mortality. Interestingly, the weekend effect had a strong geographic component. Studies conducted in North America clearly demonstrated increased weekend mortality (OR, 1.08; 95% CI, 1.03–1.12), whereas studies based in Europe (OR, 1.05; 95% CI, 0.99–1.13) and Asia (OR, 0.89; 95% CI, 0.63–1.25) did not.
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