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Preventable adverse drug events in hospitalized patients

A comparative study of intensive care and general care units

Cullen, David J. MD, MS; Sweitzer, Bobbie Jean MD; Bates, David W. MD; Burdick, Elisabeth MS; Edmondson, Amy PhD; Leape, Lucian L. MD

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Objectives  To compare the frequency and preventability of adverse drug events and potential adverse drug events in intensive care units (ICUs) and non-ICUs. To evaluate systems factors involving the individual caregivers, care unit teams, and patients involved in each adverse drug event by comparing ICUs with non-ICUs and medical ICUs with surgical ICUs.

Design  Prospective cohort study. Participants included all 4,031 adult admissions to a stratified, random sample of 11 medical and surgical units in two tertiary care hospitals over a 6-month period. Units included two medical and three surgical ICUs and four medical and two surgical general care units.

Setting  Two tertiary care hospitals: Eleven medical and surgical units, including two medical and three surgical ICUs.

Patients  Adult admissions (n = 4,031).

Interventions  None.

Measurements and Main Results  Rate of preventable adverse drug events and potential adverse drug events, length of stay, charges, costs, and measures of the unit's environment.

Incidents were detected by stimulated self-report by nurses and pharmacists and by daily review of all charts by nurse investigators. Incidents were subsequently classified by two independent reviewers as to whether they represented adverse drug events or potential adverse drug events and as to severity and preventability. Those individuals involved in the preventable adverse drug event and potential adverse drug event underwent detailed interviews by peer case-investigators.

The rate of preventable adverse drug events and potential adverse drug events in ICUs was 19 events per 1000 patient days, nearly twice that rate of non-ICUs (p < .01). The medical ICU rate (25 events per 1000 patient days) was significantly (P < .05) higher than the surgical ICU rate (14 events per 1000 patient days). When adjusted for the number of drugs used in the previous 24 hrs or ordered since admission, there were no differences in rates between ICUs and non-ICUs. ICU acuity, length of stay, and severity of the adverse drug event were greater in ICUs than non-ICUs, but there were no differences between medical ICU and surgical ICU patients. Structured interviews indicated almost no differences between ICUs and non-ICUs for many characteristics of the patient, patient care team, systems, and individual caregivers.

Conclusions  The rate of preventable and potential adverse drug events was twice as high in ICUs compared with non-ICUs. However, when adjusted for the number of drugs ordered, there was no greater likelihood for preventable adverse drug events and potential adverse drug events to occur in ICUs than in non-ICUs. Preventable adverse drug events and potential adverse drug events occurred in units that functioned normally and involved caregivers who were working under reasonably normal circumstances, not at the extremes of workload, stress, or a difficult environment. (Crit Care Med 1997; 25:1289-1297)

From the Departments of Anaesthesia (Drs. Cullen and Sweitzer), Massachusetts General Hospital and Harvard Medical School; Division of General Medicine, Department of Medicine (Dr. Bates), Brigham & Women's Hospital; Department of Health Policy and Management (Ms. Burdick and Dr. Leape), Harvard School of Public Health; Department of Psychology (Dr. Edmondson), Harvard University, Boston, MA.

See Appendix for a listing of the members of the Adverse Drug Event Prevention Study Group.

Supported, in part, by research grant R01-HS07107-01 from the Agency for Health Care Policy and Research, and by a grant from the Risk Management Foundation.

© Williams & Wilkins 1997. All Rights Reserved.