Elsevier

The Lancet

Volume 356, Issue 9225, 15 July 2000, Pages 185-189
The Lancet

Articles
Hospital mortality in relation to staff workload: a 4-year study in an adult intensive-care unit

https://doi.org/10.1016/S0140-6736(00)02478-8Get rights and content

Summary

Background

Few studies have examined mortality rates in relation to the workload of hospital staff. We investigated this issue in one adult intensive-care unit (ICU) in the UK.

Methods

We measured ICU workload per shift during each patient's stay for all admissions between 1992 and 1995 that met criteria for adjustment of mortality risk by the APACHE II equation (n=1050). APACHE II data were validated by one observer. Measures of workload in each patient's stay included occupancy, total ICU nursing requirement as defined by the UK Intensive Care Society, and the ratio of occupied to appropriately staffed beds. Over the period, staffing was appropriate for between 4·1 and 5·3 occupied beds (1·3 nurses per patient).

Findings

There were 337 deaths, 49 more (95% CI 34–65) than predicted by the APACHE II equation. 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 [1·9–5·0]) in patients exposed to high than in those exposed to low ICU workload, defined by average nursing requirement per occupied bed and peak occupancy; the unadjusted odds ratio for this comparison was 4·0 (2·6–6·2). After exclusion of measures of nursing requirement, adjusted mortality increased with the ratio of occupied to appropriately staffed beds during each patient's stay. All logistic regression models fitted the data satisfactorily.

Interpretation

Variations in mortality may be partly explained by excess ICU workload. This methodology may have implications for planning and clinical governance.

Introduction

Patients in intensive-care units (ICUs) could be at greater risk when nursing or medical workload is high than during periods of lower workload. Under these circumstances, the risks of iatrogenic complications,1 human error,2 delayed weaning from mechanical ventilation,3 and hospital-acquired infection4, 5, 6 could all increase, with potentially adverse consequences. To provide guidance on appropriate workload, the UK Intensive Care Society7 has proposed a nursing dependency schedule recommending the numbers of nurses required for different types of patients. We investigated whether hospital mortality is independently related to nursing requirement and other measures of workload, after adjusting for risk by use of the APACHE II (Acute Physiology and Chronic Health Evaluation) equation.8, 9, 10

Section snippets

Patients and staffing policy

This retrospective analysis was done on data from a prospective cohort study of all admissions to the ICU at Ninewells Hospital, Dundee, Scotland, between Jan 1, 1992, and Dec 31, 1995. The unit provides medical and surgical intensive care, with the exception of patients who have undergone cardiac surgery and some types of neurosurgery, for a population of 440 000 in Tayside and North Fife. Throughout the study, the ICU medical establishment provided for continuous cover by one consultant, one

Measures of workload

Occupancy per shift was the highest number of ICU beds occupied each shift, and peak occupancy was the highest occupancy per shift during the patient's stay. Nursing requirement per shift, recorded by the senior nurse at the end of each shift, was the highest number of nurses required for the ICU according to the recommendations of the UK Intensive Care Society7 (0·5 nurses per patient per shift for patients who are spontaneously breathing and need simple monitoring only; 1·0 for artificially

Statistical analyses

Statistical analyses were undertaken with SPSS (version 8·0). For each patient, the predicted risk of mortality, R, was calculated from the APACHE II equation.8 We did univariate analyses to test how strongly each measure of ICU workload was individually associated with observed mortality, having adjusted for logit (R)—ie, In(R/1-R). All measures of ICU workload that were significant (p<0·05) in univariate analysis were then fitted, with logit (R), in multivariate models of mortality by forward

Results

There were 1286 admissions during the study period. 236 were excluded: 88 patients were younger than 16 years; 21 were discharged from the ICU within 8 h; 36 died in the ICU within 8 h; 61 were readmitted to the ICU without being discharged from the hospital; 28 were transferred from another ICU; and two had burns. Thus, there were 1050 separate episodes in the cohort (table 1), representing 1025 patients, because 25 episodes were readmissions after discharge home. Among the 1050 episodes,

Discussion

We found that patients exposed to high ICU workload were more likely to die than those exposed to lower workload, both before and after adjustment for risk by the APACHE II equation. 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.

This study recruited a complete cohort of all admissions eligible for assessment by the APACHE II equation

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