ICU Nursing Staff Workload and Patient Mortality
Abstract & Commentary
Synopsis: Among 1050 adult patients admitted to an ICU, those exposed to high nursing staff workload were more likely to die than those exposed to a lower workload, both before and after adjusting for severity of
illness.
Source: Tarnow-Mordi WO, et al. Lancet 2000;356: 185-189.
This retrospective study from scotland examined outcomes among all patients admitted to a community hospital’s medical-surgical ICU during a four-year period in relation to staff workload. Tarnow-Mordi and colleagues hypothesized that high workload might exert an effect on outcome by altering the frequency of human error, by delaying weaning from mechanical ventilation, or by increasing the incidence of nosocomial infections. They used a locally-agreed formula to calculate the number of appropriately staffed beds, and the APACHE II equation to assess severity of illness, for four categories of admission. Medical staffing in the unit did not change during the study period.
Of 1286 ICU admissions during the study period, 236 were excluded from the study (too young, discharge within 8 hours, died within 8 hours, readmitted to ICU, transferred from another ICU, burns), leaving 1050 admissions for data analysis. Two hundred twenty-six patients died in the ICU and another 111 prior to hospital discharge. This total of 337 hospital deaths was 49 (95% CI, 34-65) more than the number predicted by the APACHE II score. The ICU was full at 295 (28%) admissions; median occupancy was 5.8 beds, and median nursing requirement was 1.6 per patient.
On multiple logistic regression analysis, adjusted mortality was more than two times higher (odds ratio, 3.1, 95% CI, 1.9-5.0) in patients exposed to high than in those exposed to low workload. After exclusion of measures of nursing requirement, adjusted mortality increased with the ratio of occupied to appropriately staffed ICU beds. The three measures of ICU workload most strongly associated with mortality were peak occupancy, average nursing requirement per occupied bed per shift, and the ratio of occupied to appropriately staffed beds. Tarnow-Mordi et al conclude that variations in ICU mortality may be partially explained by excess ICU workload.
COMMENT BY DAVID J. PIERSON, MD, FACP, FCCP
It has been well documented that ICU admission and discharge criteria tend to change at times of high bed occupancy, with patients tending to be sicker both on admission and on transfer out of the unit than at times when the pace is less hectic. In those circumstances, it is to be expected that the likelihood of error and of lapses in technique would increase.
Studies reporting how findings differ from what they "should have been" based on APACHE II scores or other comparisons to population-based scoring systems have their own problems, and the results of this retrospective study cannot tell us why more patients died in Tarnow-Mordi et al’s ICU during times of increased staff load. This study also cannot tell us whether increasing staffing in this particular ICU at times of increased workload would decrease mortality. However, the findings of increased mortality when staffing was most stretched, and of correlations between bed occupancy, staffing, and patient mortality, are consistent with common sense and my own experience in the ICU, given the known effects of nosocomial infections and clinician error on outcomes.
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