Risk factors and prediction of postoperative delirium in elderly hip-surgery patients: implementation and validation of a medical risk factor model

OBJECTIVES: To evaluate risk factors for postoperative delirium in a cohort of elderly hip-surgery patients and to validate a medical risk stratification model. DESIGN: Prospective cohort study. SETTING: Medical school-affiliated general hospital in Alkmaar, the Netherlands. PARTICIPANTS: Six hundred three hip-surgery patients aged 70 and older screened for risk factors for postoperative delirium. MEASUREMENTS: Predefined risk factors for delirium were assessed on admission. One point was assigned for each of four risk factors present, resulting in three groups: low, intermediate, and high risk. Baseline screening and assessment included the Mini-Mental State Examination, the standardized Snellen test for visual impairment, chart review to determine Acute Physiological and Chronic Health Evaluation II score, and blood urea nitrogen to creatinine ratio. The primary outcome was postoperative delirium, as defined using Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, and Confusion Assessment Method criteria. All patients were screened daily for delirium. RESULTS: Incidence of delirium was 3.8% in the low-risk group (P<.001), 11.1% in the intermediate-risk group (P=.27, relative risk (RR)=3.0), and 37.1% in the high-risk group (P<.001, RR=9.8). Cognitive impairment at admission had the highest predictive value for postoperative delirium (coefficient of determination=0.15). Contrary to previous findings, age was an independent predictive factor for delirium. Moreover, postoperative delirium was four times as frequent in acute patients as in elective hip-replacement patients. CONCLUSION: The medical risk factor model is valid for elderly hip-surgery patients. Cognitive impairment, age, and type of admission are important risk factors for delirium in this surgical population.