Benzodiazepine use as a cause of cognitive impairment in elderly hospital inpatients.

BACKGROUND

Benzodiazepine drugs are used very frequently by the elderly and have been associated with a number of untoward events in them. In an earlier publication, we showed that there was an association between benzodiazepine use and episodes of confusion in hospital. The purpose of this study was to examine that association in more detail by studying only patients with intact cognitive function on admission and by taking into consideration a range of demographic, drug use, and clinical confounders.

METHODS

A prospective cohort study was carried out of inpatients who had normal cognitive function on admission to hospital. The subjects were 418 hospital inpatients who had a normal result of a Mini-Mental State Examination (MMSE) performed within 24 hours of admission. They were aged 59-88 years. A clinical history and detailed drug use history were taken on admission and then the patients were followed prospectively for 10 days or until discharge, whichever was sooner. The MMSE was repeated every 2 days and all significant clinical events and episodes of delirium noted.

RESULTS

10.8% (95% Confidence Interval [CI]: 7.8-13.8%) of patients developed cognitive impairment (as indicated by a decrease in the MMSE). Factors that were statistically significantly related to the development of cognitive impairment included admission diagnoses of cancer or central nervous system (CNS) disease, alcohol consumption > 40 gms/day, hypoxia, and presence of benzodiazepines in the urine on admission. After adjusting for age, alcohol consumption, and admission diagnoses, those who reported taking benzodiazepines in daily doses equivalent to 5 mg or more of diazepam were at significantly higher risk of cognitive impairment than those who had not taken benzodiazepines (adjusted odds ratio = 3.5; 95% CI: 1.4-8.8). Twenty-one (5.0%, 95% CI: 2.9-7.1%) patients developed delirium as defined by the DSM-IIIR criteria. Age and hypoxia were statistically significantly related to the development of delirium. Due to the small number of cases of delirium, the power of the study to detect significant associations was low.

CONCLUSIONS

Elderly hospital inpatients who have intact cognitive function on admission to hospital have a low risk of developing cognitive impairment and delirium during their hospital stay. In this population, however, benzodiazepine use accounted for 29% of cases of cognitive impairment which did occur. The data also suggest that dehydration, urinary retention, and an admission diagnosis of CNS disease may be important risk factors for delirium.