Effect of intensive care unit environment on in-hospital delirium after cardiac surgery

Objectives: The etiology of postcardiac surgery delirium is complex. Our primary objective was to determine the effect of the postoperative environment on the prevalence of delirium by examining the in-hospital delirium rates in 2 postoperative intensive care units with differing physical infrastructure. We further sought to identify other risk factors associated with in-hospital delirium. Methods: The rates of postoperative delirium were retrospectively examined in consecutive cardiac surgery patients during 2 separate 6-month periods. Environment 1 was characterized by a lack of physical barriers between bed spaces and was windowless, and environment 2 consisted of private rooms with physical barriers for each patient and with wall-to-wall exterior windows. Univariate and multivariate analyses to determine the risk factors associated with in-hospital delirium, including the effect of environment, were undertaken. Results: Of the 1010 patients studied, 148 (14.7%) experienced in-hospital delirium after cardiac surgery. The prevalence of delirium was not significantly different between environments 1 and 2 (16.1% vs 13.5%; P = .25). However, in patients younger than 65 years, the proportion of intensive care unit days on which delirium occurred was greater in environment 1 than in environment 2 (5.4% vs 1.7%; P = .006). Postoperative stroke or transient ischemic attack, mechanical ventilation longer than 24 hours, age 65 years or older, concomitant coronary artery bypass grafting and valve surgery, prehospital admission benzodiazepine use, a requirement for any postoperative blood product transfusion, and postoperative renal insufficiency were identified as risk factors. Conclusions: The intensive care unit environment did not have a significant effect on the overall prevalence of delirium. However, that does not preclude the possibility that the intensive care unit environment might interact with other factors, such as age, in a complex manner. Attempts to reduce delirium by adjusting the intensive care unit environment alone will likely not be sufficient, and instead will require a more comprehensive multimodal approach.