Postoperative delirium after major orthopedic surgery

ARTICLE HIGHLIGHTS

Research background

Postoperative delirium (POD) is one of the most common complications in older adult patients undergoing elective surgery. The reported incidence ranges from 3%-25% after elective surgery. Many perioperative characteristics have been associated with the development of POD including increased length of recovery and hospital stay, as well as increased morbidity and mortality. Fixed risk factors often associated with POD include advanced age, pre-existing central nervous system deficits, psychiatric disease, alcohol abuse, emergency surgery and the presence of multiple comorbidities.

Research motivation

Delirium is one of the most common complications in older adult patients undergoing elective surgery. Few studies have compared, within the same institution, the type of surgery, risk factors and type of anesthesia and analgesia associated with the development of delirium.

Research objectives

We investigated the following three questions: (1) What is the incidence of POD after non-ambulatory orthopedic surgery at a high-volume orthopedic specialty hospital?; (2) Does surgical procedure influence incidence of POD after non-ambulatory orthopedic surgery?; and (3) For POD after non-ambulatory orthopedic surgery, what are modifiable risk factors?. Exploring these questions will help us determine how to treat patients at higher risk for POD when undergoing an orthopedic procedure.

Research methods

Common epidemiological research methodology and statistical analyses were used in this investigation. Electronic health records were collected and preliminary descriptive statistical analysis were conducted. Frequency counts and percentages for discrete variables and median, intra-quartile range, and minimum and maximum values for continuous variables were reported. Crude inferential analysis consisted of Chi-square and Fisher Exact tests for discrete comparisons and independent samples t-tests for continuous variables. When continuous variables failed to meet the assumption of normality using the Kolmogorov-Smirnov test, non-parametric Mann Whitney U tests were used in place of t-tests. Multivariable logistic regression analysis was used to identify potential risk factors POD while adjusting for any potential confounding.

Research results

Of 78492 surgical inpatient surgeries, the incidence from 2009 to 2014 was 1.2% with 959 diagnosed with POD. The incidence of POD was higher in patients undergoing spinal fusions (3.3%) than for patients undergoing total hip arthroplasty (THA) (0.8%); THA patients had the lowest incidence. Also, urgent and/or emergent procedures, defined by femoral and pelvic fractures, had the highest incidence of POD (7.2%) than all other procedures. General anesthesia was not seen as a significant risk factor for POD for any procedure type; however, IV patient-controlled analgesia (PCA) was a significant risk factor for patients undergoing THA [Odds ratio (OR) = 1.98, 95% confidence interval (CI): 1.19 to 3.28, P = 0.008]. Significant risk factors for POD included advanced age (for THA, OR = 4.9, 95%CI: 3.0 to 7.9, P < 0.001; for total knee arthroplasty (TKA), OR = 2.16, 95%CI: 1.58 to 2.94, P < 0.001), American Society of Anesthesiologists (ASA) score of 3 or higher (for THA, OR = 2.01, 95%CI: 1.33 to 3.05, P < 0.001), multiple medical comorbidities, hyponatremia (for THA, OR = 2.36, 95%CI: 1.54 to 3.64, P < 0.001), parenteral diazepam (for THA, OR = 5.05, 95%CI: 1.5 to 16.97, P = 0.009; for TKA, OR = 4.40, 95%CI: 1.52 to 12.75, P = 0.007; for spine fusion, OR = 2.17, 95%CI: 1.19 to 3.97, P = 0.01) , chronic opioid dependence (for THA, OR = 7.11, 95%CI: 3.26 to 15.51, P < 0.001; for TKA, OR = 2.98, 95%CI: 1.38 to 6.41, P = 0.005) and alcohol dependence (for THA, OR = 5.05, 95%CI: 2.72 to 9.37, P < 0.001; for TKA, OR = 6.40, 95%CI: 4.00 to 10.26, P < 0.001; for spine fusion, OR = 6.64, 95%CI: 3.72 to 11.85, P < 0.001). Many of the risk factors identified have been cited in previous reports and are not amenable to modification: advanced age, medical comorbidities, and a history of psychiatric disease. However, some risk factors such as pre-existing narcotic dependence, alcoholism, and hyponatremia are potentially modifiable. In addition to surgical procedure, type of anesthesia and type of postoperative analgesia may affect the incidence of POD and as such be targeted in an attempt to reduce the incidence of POD.

Research conclusions

The incidence of POD reported in this study is lower than what has been reported in many previous studies. Even in patients greater than 70 years old, our reported incidence of 2.5% is considerably below the reported rates of 15%-20% after elective surgery and 50% after the repair of hip fractures. The incidence of delirium varied between the various non-ambulatory surgical procedures. Pelvic and hip fractures demonstrated the highest rate followed by spinal fusions and then knee arthroplasty. Patients undergoing TKA are older, generally have more pain, increased comorbidities, lose more blood with subsequent increased intravenous fluid infusions, and are hospitalized longer at our institution than those undergoing THA. All of these factors could have contributed to an increase in POD. We did not find arthroplasty patients undergoing general anesthesia had a higher risk of POD than patients who received a regional anesthetic. However, this difference was present in the type of postoperative analgesia received for THA patients; epidural PCA versus intravenous PCA. We found that preoperative narcotic dependence was a major risk factor for the development of POD for THA, TKA and spine fusion patients. Opioid-tolerant patients require higher doses of postoperative opioids, and their pain is more difficult to control. The administration of postoperative opioids, particularly intravenous PCA, has been associated with sleep disturbances, cognitive impairment, and delirium. Some studies have also suggested an association between ketamine administration and postoperative confusion. However, perioperative administration of ketamine is often used to manage chronic pain in patients and reduce narcotic requirements. Hence, a direct association between ketamine and delirium is inconclusive. In this study and others, the postoperative administration of diazepam was associated with the development of POD. Diazepam is not utilized at this institution to treat postoperative confusion, but is instead used to treat anxiety or to prevent benzodiazepine withdrawal. Entering surgery as an opioid tolerant patient significantly increases the risk of POD and all efforts should be aimed at reducing the preoperative narcotic requirements of these patients and a postoperative analgesic protocol which emphasizes a non-narcotic approach should be used. For those patients at risk for POD a multifactorial intervention approach which includes multi-modal analgesia which de-emphasizes opioids, a reduction in the administration of psycho-active medications, preoperative alcohol use counselling and abstinence, early postoperative ambulation and possible early intervention with dexmedetomidate or atypical anti-psychotic medications is recommended for patients undergoing elective orthopedic inpatient surgery.

Research perspectives

We hypothesized that regional anesthesia, postoperative opioid sparring techniques, and early ambulation were responsible for the lower incidence of POD in our arthroplasty patients. Future research may involve a program designed for elderly patients at risk for POD undergoing total joint arthroplasty and should include: A regional anesthetic with reduced intravenous sedation; when feasible, local anesthetic blocks for postoperative analgesia; opioid sparring medications including acetaminophen and nonsteroidal anti-inflammatory drugs; time and place orienting by nursing staff; undisturbed sleep while in the hospital; and early ambulation and discharge from the hospital. The incidence of POD in this group should then be compared to controls. The spine fusion patient population, which has a higher incidence of POD, could also be used in future research studies using the postoperative protocol designed for arthroplasty patients outlined above with an alteration to the anesthetic protocol. Spine fusion patients require general anesthesia – in these procedures rather than using a regional anesthetic or local anesthetic block, the general anesthesia can be administered to reduce the patient’s exposure to medications that have the potential to produce delirium. The anesthetic can include intravenous dexmedetomidate, lidocaine and ketamine, all of which will reduce narcotic administration. Furthermore, since preoperative narcotic dependence was associated with POD, future research should also focus on preoperative opioid reduction and clear postoperative pain management expectations.