Objective: To better understand variation in reported rates of delirium, this study characterized delirium occurrence rate by department of service and primary admitting diagnosis.
Method: Nine consecutive years (2005-2013) of general hospital admissions (N=831,348) were identified across two academic medical centers using electronic health records. The primary admitting diagnosis and the treating clinical department were used to calculate occurrence rates of a previously published delirium definition composed of billing codes and natural language processing of discharge summaries.
Results: Delirium rates varied significantly across both admitting diagnosis group (X210=12786, p<0.001) and department of care (X26=12106, p<0.001). In both cases obstetrical admissions showed the lowest incidences of delirium (86/109764; 0.08%) and neurological admissions the greatest (2851/25450; 11.2%). Although the rate of delirium varied across the two hospitals the relative rates within departments (r=0.96, p<0.001) and diagnostic categories (r=0.98, p<0.001) were consistent across the two institutions.
Conclusions: The frequency of delirium varies significantly across admitting diagnosis and hospital department. Both admitting diagnosis and department of care are even stronger predictors of risk than age; as such, simple risk stratification may offer avenues for targeted prevention and treatment efforts.
Keywords: Acute confusional state; Delirium; Electronic health record; Epidemiology.
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