Hospital Mortality with Different Days and Times of ICU Admission: Up and Running 24/7

Abstract & Commentary

Synopsis: Among 56,250 British ICU patients, hospital mortality rates were higher among those admitted on the weekend or at night, but the differences disappeared when confounding by illness severity and other aspects of case mix were eliminated.

Source: Wunsch H, et al. Intensive Care Med. 2004:30:895-901.

Wunsch and colleagues examined data from 75,621 consecutive admissions to 102 ICUs in England, Wales, and Northern Ireland to determine whether the day of the week or the time of the day patients were admitted affected hospital mortality. They excluded patients who spent less than 8 hours in the ICU, were younger than 16, were admitted after burns or cardiac surgery, were transferred from another ICU, or had insufficient data for determination of APACHE II scores. This left 56,250 patients for evaluation. The 24-hour day was divided into day (8 am-6 pm), evening (6 pm-midnight) and night (midnight-8 am) periods, to correspond with usual working schedules in ICUs in the United Kingdom.

There were almost twice as many ICU admissions on any given weekday as on Saturday or Sunday, mainly reflecting differences in scheduled surgery. In addition, substantially more patients were admitted during the day than in the evening, and during the evening than at night. Patients admitted on weekends had higher crude hospital mortality than patients admitted mid-week (Saturday vs weekends, 35% vs 27%; crude odds ratio, 1.41; 95% confidence interval 1.32-1.52). Night admissions were also associated with higher mortality compared with daytime admissions (crude mortality 34% vs 27%; OR, 1.43; 95% CI, 1.37-1.51). The differences diminished in each instance when adjusted using the overall UK APACHE II model, but remained statistically significant. However, when adjustment was carried out using individual components of the APACHE II model, the differences disappeared for both day of week and time of day. Thus, after appropriate adjustment for case mix, the day of the week, and time of day patients were admitted to the ICU were not associated with significant differences in hospital mortality.

Comment by David J. Pierson, MD

Patients admitted to the ICU on weekends, or at night regardless of the day of the week, are more likely to die in the hospital than patients admitted during the week or during the day. However, interpreting these differences is tricky. It is tempting to assume that fewer physicians, nurses, and support personnel are around at night and on the weekend, that diagnostic and other procedures would be less available, and that these things might lead to worse patient outcomes. But such does not turn out to be the case, at least in this study. Instead, patients admitted during the week and during the day tended to be postoperative and other elective admissions, with less severity of illness and less likelihood of dying in the hospital. Patients admitted on Saturday or Sunday, or in the middle of the night on any day of the week, are sicker and thus more likely to die.

There are limitations to this study with respect to the application of its findings to your practice and mine. It reflects what happens in ICUs in England, Wales, and Northern Ireland, which differs in important ways from critical care in North America. It does not include patients readmitted to the ICU (bounce-backs). And it does not sort out what happens on the ward after ICU discharge. Nonetheless, the findings of Wunsch et al support the concept that staffing in ICUs tends to be more constant around the clock and throughout the week than that on the general inpatient ward. Whether the ICUs involved were "open" or "closed," and the extent to which care was provided by trained and/or board-certified intensivists, both of which have been shown to affect patient outcomes,1,2 is also not specified in the paper. However, this study provides reassurance that concerns about the quality of care at different times of the 24-hour day and on different days of the week may be unfounded in the 24/7 environment of the ICU.


1. Carson SS, et al. JAMA. 1996;276:322-328.

2. Brown J, Sullivan G. Chest. 1989;96:127-129.

David J. Pierson, MD, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, is Editor of Critical Care Alert.