Sedation Depth During Spinal Anesthesia and the Development of Postoperative Delirium in Elderly Patients Undergoing Hip Fracture Repair

OBJECTIVE: To determine whether limiting intraoperative sedation depth during spinal anesthesia for hip fracture repair in elderly patients can decrease the prevalence of postoperative delirium.PATIENTS AND METHODS: We performed a double-blind, randomized controlled trial at an academic medical center of elderly patients (≥65 years) without preoperative delirium or severe dementia who underwent hip fracture repair under spinal anesthesia with propofol sedation. Sedation depth was titrated using processed electroencephalography with the bispectral index (BIS), and patients were randomized to receive either deep (BIS, approximately 50) or light (BIS, ≥80) sedation. Postoperative delirium was assessed as defined by Diagnostic and Statistical Manual of Mental Disorders (Third Edition Revised) criteria using the Confusion Assessment Method beginning at any time from the second day after surgery.RESULTS: From April 2, 2005, through October 30, 2008, a total of 114 patients were randomized. The prevalence of postoperative delirium was significantly lower in the light sedation group (11/57 [19%] vs 23/57 [40%] in the deep sedation group; P=.02), indicating that 1 incident of delirium will be prevented for every 4.7 patients treated with light sedation. The mean ± SD number of days of delirium during hospitalization was lower in the light sedation group than in the deep sedation group (0.5±1.5 days vs 1.4±4.0 days; P=.01).CONCLUSION: The use of light propofol sedation decreased the prevalence of postoperative delirium by 50% compared with deep sedation. Limiting depth of sedation during spinal anesthesia is a simple, safe, and cost-effective intervention for preventing postoperative delirium in elderly patients that could be widely and readily adopted.Trial Registration: clinicaltrials.gov Identifier: {"type":"clinical-trial","attrs":{"text":"NCT00590707","term_id":"NCT00590707"}}NCT00590707BIS = bispectral index; CAM = Confusion Assessment Method; CI = confidence interval; ICU = intensive care unit; MMSE = Mini-Mental State Examination; NNT = number needed to treat; OR = odds ratio; PACU = postanesthesia care unitPostoperative delirium occurs in elderly patients at an overall prevalence of 10% to 37%.^1,2 The prevalence ranges from 0% to 73%, depending on the study and type of surgery,² with a prevalence of 16% to 62% after hip fracture repair.^3-5 Although postoperative delirium usually resolves within 48 hours of onset,⁶ delirium can persist and is associated with poor functional recovery, increased length of stay, higher costs, and greater likelihood of placement in an assisted living facility after surgery.^3,5,7-13 Therefore, interventions capable of reducing the occurrence of postoperative delirium would be important from a public health perspective, but relatively few proposed interventions have proven efficacious.^14-16Several demographic and perioperative variables are associated with postoperative delirium in elderly patients after hip fracture repair, the most important of which is preoperative dementia.^3,7,17-20 Other risk factors for postoperative delirium include age, systemic disease, functionality, and psychoactive medications.^3,19 Inhalational and intravenous anesthetics, opioids, benzodiazepines, and anticholinergic drugs are all known or suspected risk factors for postoperative delirium.^21-26 Although perioperative opioids are a risk factor for postoperative delirium, they are difficult to avoid after major surgery,^17,25 especially because undertreated pain may increase the risk of postoperative delirium.¹⁷ Transfusion and perioperative medical complications may also be important.³ Unfortunately, most of these risk factors are not readily modified at the time of surgery.For editorial comment, see page 12Anesthetic technique is a potentially modifiable risk factor for postoperative delirium. Although administration of many drugs can be avoided or limited with regional anesthetic techniques and reductions in the prevalence of postoperative delirium have been observed with regional anesthesia, these results are inconsistent.^27,28 This inconsistency may be explained by reports that sedation levels consistent with general anesthesia are frequently observed during regional anesthesia^29-32 and, at least in an intensive care setting, that sedation level is an important risk factor for delirium.²³ The intravenous anesthetic propofol is commonly used to provide intraoperative sedation during spinal anesthesia and other regional anesthetics. Although propofol may have longer-term effects on some neurons of the central nervous system in vitro,³³ it is generally considered safe and without persistent aftereffects.We hypothesized that minimizing sedation depth during spinal anesthesia for hip fracture repair in elderly patients could decrease the occurrence of postoperative delirium. Therefore, we performed a randomized controlled trial that compared the prevalence of postoperative delirium after hip fracture repair with spinal anesthesia with either deep or light propofol sedation.