Nursing Center - Journal Issue

Keywords: cognitive impairment, delirium, dementia, elderly, postoperative delirium, surgery

Abstract

Overview: Nearly 40% of all surgeries in the United States are performed on adults ages 65 and older. One of the most common surgical complications in this population is postoperative delirium, which is associated with extended lengths of stay, higher patient care costs, increased morbidity, and greater risk of death. This review evaluates risk factors for postoperative delirium in elderly patients, discusses screening and assessment instruments, and examines intervention strategies.

In 2009, more than 37% of all interventional and surgical procedures in the United States were performed on adults ages 65 and older. Patients in this age group accounted for more than 57% of all coronary artery bypass grafts and 50% of all large bowel resections.1 Given that the average 75-year-old American "has three chronic conditions and uses five prescription drugs,"2 it's not surprising that postoperative delirium is a frequent complication of surgery in elderly patients, with reported incidence rates ranging from 9% in patients ages 50 and older who have undergone elective noncardiac surgery3 to nearly 18% in patients over age 65 who have undergone emergency surgery4 and as high as 87% among elderly patients in ICUs.5 Because postoperative delirium is associated with extended lengths of stay, higher patient care costs, increased morbidity with subsequent functional decline, and greater risk of death,4, 6-9 early diagnosis and resolution is likely to produce the most favorable outcomes.7, 8, 10-13

Figure. Photo Arni ... - Click to enlarge in new window

The purpose of this review is to evaluate predisposing and precipitating risk factors for postoperative delirium in elderly patients, to discuss tools used to assess preoperative risk and postoperative cognitive function in this patient population, and to examine potential intervention strategies. Over the past 10 years, a number of predisposing clinical factors have been associated with postoperative delirium in geriatric patients, including various comorbid conditions and advanced age itself.4, 7, 8, 12, 14 Precipitating factors, defined as "noxious insults or hospitalization-related factors" have also been said to contribute to delirium.15 Because many risk factors are potentially modifiable, identification provides an opportunity for effective intervention.

SELECTION CRITERIA

To identify studies for evaluation, I conducted a comprehensive literature search of all English-language articles concerned with postoperative delirium in elderly adults that were published between January 1, 2005, and December 31, 2010, and included in Ovid, MEDLINE, and the Cumulative Index to Nursing and Allied Health Literature (CINAHL). In addition, I retrieved some nonindexed, Internet articles through a Google search. Search terms included postoperative delirium, delirium, delirium superimposed on dementia, surgery, advanced age, elderly, postoperative delirium interventions, and such suspected risk factors for delirium as hypoxia, cognitive impairment, compromised functional status, sensory impairment, sepsis, hyperglycemia, hypoglycemia, preexisting medical conditions, physical restraint, and sleep deprivation.

The initial literature search yielded a total of 2,204 articles, after which duplicates, review articles, and studies that did not address delirium or cognitive decline during the postoperative period were excluded (1,980). The remaining 224 articles were further evaluated, and additionally excluded were any in which postoperative cognitive decline was related to alcohol, brain injury, mental disability, or other primary causes; subjects were under age 65; research was not primary (for example, meta-analyses); or investigators failed to assess either delirium risk factors or assessment methods (Figure 1). Ultimately, 12 primary research studies were included for review (Table 1).4, 7, 8, 12, 16-23 Predisposing and precipitating factors for postoperative delirium were investigated in seven and three of the studies reviewed, respectively (see Table 2 4, 7, 8, 12, 16, 18, 19, 21-23); one study compared assessment tools; and one tested a nonpharmacologic intervention strategy.

Figure 1 - Click to enlarge in new window

Figure 1. Study Selection and Application of Exclusion Criteria

Table 1 - Click to enlarge in new window

Table 1. Research Studies Reviewed

Table 2 - Click to enlarge in new window

Table 2. Factors Contributing to Postoperative Delirium in Elderly Surgical Patients

PREDISPOSING RISK FACTORS

Advanced age was a consistent, well-established risk factor for postoperative delirium in most studies addressing risk.4, 7, 8, 12, 16, 18, 21 Likewise, various comorbidities were associated with postoperative delirium in several studies, with some having a significant effect on mortality rate in these patients.4, 7, 8, 12, 16, 21

Independent variables. When Ansaloni and colleagues studied 351 patients over the course of 357 surgical admissions, they found that five clinical factors were significant predictors of postoperative delirium: age over 75; comorbidity (as evidenced by a Cumulative Illness Rating Scale score of 8 or higher); preoperative hyperglycemia or hypoglycemia; psychological distress (as indicated by a Hospital Anxiety and Depression Scale score of 15 or more); and preoperative cognitive impairment (as demonstrated by a Short Portable Mental Status Questionnaire score of 7 or lower).4 In this study, the incidence of postoperative delirium was 13.2% overall and 17.9% among patients undergoing emergency surgery. Because patients undergoing emergency surgery tend to be more compromised than those undergoing elective surgery, the inclusion of these patients may limit the generalizability of these findings to other settings, as may the exclusion of patients with such neuropsychiatric disorders as speech, sensory, and gross cognitive impairments.

In a prospective descriptive survey of 71 patients ages 65 or older who were undergoing elective abdominal surgery, univariate analysis showed age over 74, longer ICU stay, longer hospital stay, greater number of postoperative complications, low preoperative cognitive screening test scores, and higher intraoperative American Society of Anesthesiologists scores to be significant risk factors for postoperative delirium.8 After multivariate analysis, however, only age over 74 was significant. In this study, the incidence of postoperative delirium was 24%, and the mortality rate was significantly higher in patients who developed postoperative delirium than in those who did not. The generalizability of the findings is limited by the small sample size and the fact that investigators did not control for medication use.

Inadequate nutrition and functional impairment. Of 228 patients consecutively admitted to a 650-bed teaching hospital for major abdominal surgery, Ganai and colleagues studied 89 they identified as being at high risk for postoperative delirium based on the presence of at least three of the following previously validated risk factors: severe illness, visual impairment, cognitive impairment, and dehydration.7 In this group, they found that poor preoperative nutritional status and functional impairment were significant independent predictors of postoperative delirium, which in turn was significantly associated with both a 14-day or longer increased length of stay and an increased risk of death. Although all patients in the study were at least 70 years of age, those who developed postoperative delirium were, on average, four years older than those who did not (81 versus 77 years), a difference that was statistically significant (P = 0.005). At 60%, the overall incidence of postoperative delirium in these patients was higher than expected, which the researchers suggest may be linked to suboptimal care in areas previously associated with delirium, such as prolonged bed rest, uncontrolled pain, hypoxia, poor glycemic control, and use of such medications as meperidine, hydroxyzine, benzodiazepines, diphenhydramine, tricyclic antidepressants, muscle relaxants, and barbiturates. One major weakness in this study is that the researchers did not use a standard assessment tool to evaluate preoperative function and nutritional status but instead looked for keywords in the medical records that provided evidence of deficits. This may have caused them to underestimate the true incidence of preoperative functional impairment and malnutrition.

Preoperative cognitive function. In a small prospective study, Morimoto and colleagues demonstrated that cognitive function, cerebral oxygen saturation, and the incidence of postoperative delirium are closely related in elderly patients undergoing major abdominal surgery.21 Researchers evaluated cognitive function in 23 patients over age 65 who were undergoing elective abdominal surgery, using the Hasegawa dementia score (a brief, standardized dementia-screening scale) and the kana-hiroi test (an auditory verbal learning test). After excluding three patients with documented cerebral pathology or baseline dementia, demonstrated by a Hasegawa dementia score below 22, they reported on 20 whose advanced age, low preoperative kana-hiroi test scores, and low intraoperative cerebral oxygen saturation (as indicated by near infrared spectroscopy) were determined to be significant risk factors for postoperative delirium. After surgery, five (25%) of the patients developed delirium; those who did were significantly older than those who did not (76 +/- 4 years versus 68 +/- 3 years), had significantly lower scores on the preoperative kana-hiroi test (16 +/- 5 versus 32 +/- 10), and had significantly lower baseline regional cerebral oxygen saturation levels (60% +/- 5% versus 66% +/- 7%). Preoperative and postoperative Hasegawa dementia scores did not differ between the two groups, and preoperative and postoperative kana-hiroi test scores did not differ significantly within either group. The study's two greatest limitations are its small sample size and the fact that cerebral oxygen saturation was not monitored after surgery, so postoperative deficits may have gone unnoticed.

Preoperative executive dysfunction and depression were independently associated with a greater incidence of postoperative delirium in a prospective, observational, case-control study and retrospective chart review conducted by Smith and colleagues.12 Of 998 patients undergoing major noncardiac surgery, 35 were identified as having postoperative delirium by Confusion Assessment Method (CAM) screening and retrospective chart review. Risk increased with age and comorbidity. Patients exhibiting both executive dysfunction and clinically significant levels of depression were at greatest risk for developing postoperative delirium. Because patients with a history of psychiatric illness or cognitive impairment were excluded from the study, findings may fail to reflect the full impact of depression or executive dysfunction on risk of postoperative delirium.

Bellelli and colleagues investigated the relationship between delirium superimposed on dementia, which is highly prevalent among hospitalized geriatric patients, and associated mortality.16 From 1,278 patients ages 65 and older who were consecutively admitted to a rehabilitation unit following surgery or other events, the researchers selected four groups of 47 each-patients with delirium superimposed on dementia, patients with delirium alone, patients with dementia alone, and patients with neither delirium nor dementia-which were matched for age, sex, and reason for admission. In patients with delirium superimposed on dementia, 12-month survival after discharge was significantly lower than in the other three groups-12 patients died, compared with five in the delirium-alone group, five in the dementia-alone group, and four in the neither-delirium-nor-dementia group. Because the study was conducted in a rehabilitation unit, however, its generalizability to other clinical settings may be limited.

Inflammatory markers. Lemstra and colleagues found no relationship between preoperative circulating inflammatory markers and delirium in their study of 68 elderly patients admitted for hip surgery, 18 of whom developed postoperative delirium. They suggest that, to determine whether rising cytokine levels are in response to an injury or are contributing to it, further research should be based on sequential cytokine measurements, taken at several time points.18

PRECIPITATING FACTORS

Most researchers agree that a combination of predisposing and precipitating factors influence the development of postoperative delirium in elderly patients.

Aspects of pain management. Both analgesia and postoperative pain have been correlated with the development of postoperative delirium.19, 22 One study that evaluated the relationship between pain management and delirium in hospitalized elderly patients showed that hearing deficits may put patients at risk for poor pain management and, therefore, delirium.22 In their retrospective medical record review involving 100 medical and surgical patients (mean age, 76.71 years) who developed delirium while hospitalized, Robinson and colleagues discovered that those with hearing deficits had received significantly less pain medication during the 24 hours preceding delirium onset than those who had other risk factors for delirium (P = 0.023). The authors suggest that hearing deficits in elderly patients contribute to poor communication between patient and caregiver and stress the importance of using assistive devices to communicate with such patients.

Moreover, among all patients, the researchers found a significant correlation between the time from admission or surgery to delirium onset and the percentage of pain medication received, with patients who experienced delirium having received only a small proportion of their ordered pain medication in the 24 hours before delirium onset. Those who received greater amounts of pain medication had a later occurrence of delirium. Physician notes showed that, in many cases, delirium was attributed to opioids; but this was without basis, since the amount of pain medication the patient received was not determined before discontinuation and, as the authors point out, previous studies demonstrate no association between most opioids and delirium. In nine cases, however, patients were receiving drugs whose cumulative effect is associated with delirium in older patients: propoxyphene and meperidine, which were given to eight patients and one patient, respectively.

The study suggests that in patients at risk for developing delirium, both unmanaged pain and some specific pain medications may be precipitating factors. Study limitations include its retrospective design, which depends heavily on accurate clinician recognition and documentation of delirium, and clinicians' failure to use a valid and reliable instrument to assess delirium.

Leung and colleagues also investigated pain and postoperative delirium, specifically focusing on whether it's feasible for patients with postoperative delirium to use patient-controlled analgesia (PCA). In a nested cohort study of 335 patients ages 65 and older who underwent noncardiac surgery, the authors determined that postoperative delirium did not limit the use of PCA.19 Patients with postoperative delirium had significantly higher visual analog scale scores for pain following surgery, but not because they were unable to use PCA. In fact, they used PCA as much or more than nondelirious patients. Although the investigators reached no conclusion about the role of causality in the relationship between postoperative delirium and pain, their findings suggest that pain could be more effectively managed in elderly patients at risk for postoperative delirium. Because this study evaluated only the early postoperative period (less than 48 hours following surgery), some cases of late-onset postoperative delirium may have been missed.

Some sedation techniques have been proposed as causative factors in the development of postoperative delirium in elderly patients. In a double-blind, randomized controlled trial by Sieber and colleagues, 114 patients ages 65 or older, with no preexisting cognitive impairment, underwent hip fracture repair under spinal anesthesia with propofol sedation.23 Patients were randomly assigned to receive either deep or light sedation, and researchers used electroencephalography with bispectral index to titrate sedation depth. Researchers found that the use of light propofol sedation halved the frequency of postoperative delirium when compared with deep sedation (19% versus 40%). Furthermore, the mean number of days of delirium during hospitalization was significantly fewer in the light sedation group than in the deep sedation group (0.5 +/- 1.5 days versus 1.4 +/- 4 days). Although the total dose of propofol was significantly higher in the deep sedation group, dose alone did not predict the occurrence of postoperative delirium. The most important predictor in this patient population was the depth of sedation. These findings suggest that limiting the depth of sedation in some spinal anesthesia procedures may be an effective strategy for preventing postoperative delirium in elderly patients. The generalizability of these results is limited to patients with only moderate or minimal dementia, because patients with severe cognitive impairment (Mini-Mental State Examination scores below 15) were excluded.

EARLY IDENTIFICATION

Luetz and colleagues compared several delirium assessment tools in a prospective cohort study that included 156 patients ages 60 or older who spent at least 24 hours in a German surgical ICU.20 The researchers concluded that the CAM-ICU and the Nursing Delirium Screening Scale (Nu-DESC) had comparable sensitivities in this population (81% and 83%, respectively). They found, however, that the specificity of the CAM-ICU was much higher than that of the Nu-DESC (95% versus 81%), and both tests performed better than the Delirium Detection Score (DDS). From this study, the researchers concluded that, because of its high specificity, the CAM-ICU is the best tool to use in an elderly surgical ICU population. A major limitation of this study is the subjects' variable lengths of ICU stay, which ranged from 24 hours to 21 days and may have biased the results. In addition, interrater reliability was determined on the basis of only 37 paired observations. Finally, although investigators attempted to minimize bias by consistently performing assessments in the same order, starting with the DDS, it's possible that earlier assessments influenced the results of subsequent assessments.

INTERVENTION

In a small blinded, controlled trial, Kolanowski and colleagues randomly assigned 16 elderly medical-surgical patients who had been admitted to a postacute care rehabilitation center with delirium superimposed on dementia to either a nonpharmacologic intervention group that engaged in cognitively stimulating activities for 30 minutes per day (n = 11) or a control group that received usual care (n = 5).17 When compared with the intervention group, the control group had a significantly greater decline in physical function and mental status over time. Although the study's small sample size made it difficult to demonstrate statistical significance, patients in the intervention group had fewer days with delirium, less severe delirium, and higher attention scores than patients in the control group, with differences approaching significance in all three areas.

DISCUSSION

Predicting postoperative delirium. In the studies reviewed, advanced age, long recognized as a risk factor for postoperative delirium, was consistently found to be an important predictor; even among elderly patients, risk increased significantly with age.4, 7, 8, 12, 21 Cognitive impairment, psychological distress, postoperative complications, glycemic abnormalities, malnutrition, and functional impairment predisposed to postoperative delirium in several studies-with inadequate nutrition, functional impairment, and dementia significantly elevating risk of death.4, 7, 8, 12, 16, 18, 21 Although the causal relationship between pain and postoperative delirium isn't clear, postoperative pain scores were higher among patients with delirium in one study,19 while pain medication appeared to delay onset of postadmission and postoperative delirium in another.22 Both of these studies suggest that pain management is often inadequate in elderly patients at risk for postoperative delirium. Depth of sedation was significantly associated with postoperative delirium, with deep sedation doubling its prevalence and significantly increasing the duration of delirium during hospitalization.23

Findings on cognitive impairment in postoperative patients are consistent with studies of hospitalized geriatric patients in general medical units. In a descriptive study evaluating patterns associated with delirium in 104 patients, researchers found that the prevalence of delirium among geriatric patients newly admitted to an acute care hospital increased significantly with severity of prior cognitive impairment.24 Among patients with mild, moderate, and severe prior cognitive impairment, prevalence of delirium, as assessed by the CAM, was 50% (24 of 48), 82% (23 of 28), and 86% (24 of 28), respectively. Degree of prior cognitive impairment significantly affected only one symptom of delirium, disorganized thinking, which occurred in 58% of patients whose prior cognitive impairment was mild and in 92% of those whose prior cognitive impairment was severe. The study authors propose training programs to prepare nurses to recognize subtle changes in mental status that may signify the development of delirium among elderly patients with a history of prior cognitive impairment.

The role of inflammatory markers in delirium has not been studied extensively. In this review, based on one study of 68 geriatric patients,18 inflammatory markers were found to have no association with postoperative delirium-a finding that is inconsistent with that of an earlier study of delirium in elderly patients hospitalized for general medical conditions, conducted by de Rooij and colleagues.25 In that study, 64 (34.6%) of 185 patients, ages 65 and older, developed delirium within 48 hours of hospital admission. Significantly more patients without delirium than with delirium had interleukin-6 and interleukin-8 levels below the detection limit (69% versus 47%, and 78% versus 55%, respectively). After adjusting for infection, age, and cognitive impairment, these differences remained significant. The authors acknowledge, however, that their study may be limited by the small number of patients with detectable cytokine levels and by the fact that cytokines were measured in peripherally sampled blood, most of which was obtained three days after admission and therefore may not accurately reflect the inflammatory processes occurring in the brain during delirium.

For patients in a general medical service, Inouye and Charpentier found five variables to be predictive of delirium during hospitalization: use of physical restraints, malnutrition, the addition of more than three medications, use of a bladder catheter, and any iatrogenic event (such as a cardiopulmonary complication, hospital-acquired infection or injury, medication-related or procedural complication, pressure sore, or fecal impaction).15 With the exception of malnutrition,7 the studies of postoperative delirium reviewed here did not investigate these risk factors.

Assessing delirium. The majority of studies in this review used the CAM to identify delirium in surgical patients.4, 12, 16-19, 23 Available in both nine- and four-item forms, the CAM has been validated for use by nonpsychiatric clinicians.26 A nonverbal form of this tool, the CAM-ICU, was found to be valid and reliable in detecting delirium in patients who are mechanically ventilated.27 In this 2001 prospective cohort study of medical and coronary ICU patients, two critical care study nurses used the test to independently rate 96 mechanically ventilated patients throughout their ICU stay, and delirium experts performed independent evaluations based on the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria. Between nurses and delirium experts, a total of 471 paired daily evaluations were collected. The CAM-ICU was shown to have sensitivity ratings of 100% (nurse 1) and 93.5% (nurse 2), specificity ratings of 97.8% (nurse 1) and 100% (nurse 2), and excellent interrater reliability ([kappa] = 0.96). Although authors of the validation study noted that the generalizability of their findings to patient populations with a lower prevalence of delirium may be limited, in the one study reviewed here that compared delirium assessment tools, the CAM-ICU was found to be the best tool for detecting delirium in elderly surgical ICU patients, being superior to both the Nu-DESC and the DDS.20

Preventing decline. The one intervention study in this review found that daily cognitive stimulation could reduce the severity and duration of postoperative delirium in patients with dementia.17 Similarly, evidence-based research has demonstrated that comprehensive programs, such as the Hospital Elder Life Program (HELP), may be effective in preventing delirium and preserving independent functioning in older hospitalized patients.28 The program's interdisciplinary staff and trained volunteers work within existing hospital units to identify patients at risk for cognitive and functional decline during the preoperative and early postoperative periods. Interventions focus on orientation and assistance with meals and ambulation; activities encourage socialization and cognitive stimulation.29 Rubin and colleagues found that HELP could reduce the incidence of delirium, while lowering patient care costs. In the seven years following implementation of the program in a 500-bed community teaching hospital, the rate of delirium dropped from 41% to 18%; length of stay was reduced by 1.8 days in patients with delirium and by 0.7 days in patients without delirium; hospital costs were significantly lowered by an estimated $7.3 million per year; and satisfaction improved among patients, families, and nursing staff.28

Neitzel and colleagues developed an approach to preventing and managing delirium in orthopedic patients, which involved the use of a multidisciplinary team (consisting of physicians, nurses, pharmacists, and a quality specialist) and a set of evidence-based orders that limited the use of indwelling catheters, set up patient routines, promoted adequate rest, encouraged pharmacist review of medications, and incorporated such integrative therapies as therapeutic touch and music.30 Over the course of a four-week trial within a tertiary care hospital, the program reduced the proportion of patients with NEECHAM Confusion Assessment Scale scores below 20 by nearly 9% compared with the proportion of such patients identified the year before program implementation.

IMPLICATIONS FOR PRACTICE

Multiple studies have demonstrated that postoperative delirium in elderly surgical patients is multifactorial in etiology.7, 8, 11, 12, 19, 21, 31 Both predisposing and precipitating factors can elevate the risk,4, 8, 14 and many of these-such as poor glycemic control, inadequate nutrition, poor pain management, medication use, and depth of intraoperative sedation-are modifiable. Once a patient is identified as being at risk, a multifactorial prevention program needs to be initiated. Prevention is the goal, and identifying risk is key to prevention.

To determine risk, use an assessment tool, such as the CAM or CAM-ICU, or apply criteria specified in the DSM-IV to establish the patient's baseline mental status.20, 27, 32, 33 (To learn more about using the CAM, see "How to Try This: Detecting Delirium" at http://bit.ly/MODqAU and the demonstration video at http://bit.ly/MnX0W8.) Researchers concur that a multidisciplinary team that addresses both preoperative and postoperative risk factors is generally most effective in preventing postoperative delirium in elderly patients.34, 35 Some researchers suggest that surgical teams for older patients should include a geriatric nursing specialist34 and that elderly surgical patients should be cared for in specialized geriatric units.36

The Nurses Improving Care for Healthsystem Elders (NICHE) program, developed at New York University in 1992, can assist hospital staff in caring for geriatric surgical patients.37 This program employs geriatric advanced practice nurses to train RNs to provide appropriate care for elderly patients and helps facilities adjust care practices to better meet their needs.

Advances in anesthesia, critical care, and surgical techniques have made geriatric surgery reasonably safe. Despite these improvements, elderly patients continue to face a high risk of postoperative delirium. A new diagnosis of delirium after hospitalization increases a patient's risk of falling sixfold.38 This is a significant concern since falls, according to the National Institutes of Health, are the leading cause of injury, loss of independence, and death nationwide for those over 65 years of age.39

Nurses are in a unique position to implement and coordinate services for their patients. Postoperative care needs to focus not only on cognition but also on ability to perform activities of daily living. This review suggests the benefit of nurses formally assessing elderly patients at risk for postoperative delirium and, upon recognizing early signs, initiating intervention measures. Formal instruments for assessing delirium should be used routinely by every nurse assessing an elderly surgical patient.