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Article

Incidence and Predictors of Postoperative Delirium in Patients Undergoing Elective Hip and Knee Arthroplasty: A Prospective Observational Study

by
James Paul
1,*,
Amir Hamid
2,†,
Heung Kan Ma
3,
Thomas Kim
4,
Lehana Thabane
5,6 and
Thuva Vanniyasingam
7,‡
1
Department of Anesthesia, McMaster University, Hamilton, ON L8S 4L8, Canada
2
Almonte General Hospital, Almonte, ON K0A 1A0, Canada
3
Department of Anesthesia, University of Toronto, Toronto, ON M5G 0A8, Canada
4
Department of Anesthesia, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
5
Department of Health Research Methods, Evidence & Impact, McMaster University, Hamilton, ON L8S 4L8, Canada
6
Biostatistics Unit, St Joseph’s Healthcare Hamilton, McMaster University, Hamilton, ON L8N 4A6, Canada
7
Cytel, Toronto, ON M6K 1E6, Canada
*
Author to whom correspondence should be addressed.
†
Current address: Department of Family Medicine, McMaster University, Hamilton, ON L8S 4L8, Canada.
‡
Current address: Biostatistics Unit, St Joseph’s Healthcare Hamilton, McMaster University, Hamilton, ON L8S 4L8, Canada.
Anesth. Res. 2025, 2(2), 11; https://doi.org/10.3390/anesthres2020011
Submission received: 17 December 2024 / Revised: 11 April 2025 / Accepted: 30 April 2025 / Published: 9 May 2025
Versions Notes

Abstract

:
Background/Objectives: Postoperative delirium has not been well explored in patients undergoing elective hip and knee arthroplasty. This study assessed the incidence of delirium in these patients in the postanesthetic care unit (PACU) and throughout their hospital admission. Predictors of postoperative delirium and impact of delirium on length of stay were also analyzed. Methods: This prospective observational study recruited patients (n = 978) with normal cognitive function presenting for elective primary hip or knee arthroplasty at a single tertiary academic center. Delirium was assessed using the Nursing Delirium Scoring Scale (NuDESC) in the PACU, and twice daily after that on postoperative days 1, 2 and 3, or until discharge, whichever came first. Results: In total, 26 (2.7%) patients developed delirium postoperatively. Unadjusted logistic regression analyses revealed that age; history of cardiovascular, central nervous system, hematologic, endocrinologic, psychiatric disease; postoperative opioid use; and ASA level were associated with an increased risk of delirium, with odds ratios (95% confidence interval) of 1.7 (1.35 to 2.11), 3.6 (1.09 to 12.25), 3.5 (1.53 to 8.03), 2.7 (1.09 to 6.45), 2.3 (1.04 to 4.97), 4.7 (2.10 to 10.70), 0.4 (0.17 to 0.89), and 2.37 (1.05 to 5.33), respectively. A Mann–Whitney U test showed no difference in PACU or hospital length of stay between patients who did and did not have delirium in the PACU (within the first hour). Conclusions: Age, ASA > 3, a history of cardiovascular disease, central nervous system disease, hematologic disease, endocrinologic disease, psychiatric disease and postoperative opioid use are individually associated with postoperative delirium. A future study with an even larger sample size is needed to further evaluate these factors in an adjusted analysis.

1. Introduction

Postoperative delirium (PD) has been extensively studied due to its significant impact on both short- and long-term outcomes for patients. It is associated with increased in-hospital mortality, extended lengths of stay, functional impairment after surgery, increased mortality up to a year after discharge, and increases in costs of care [1,2,3,4,5,6,7,8,9,10].
Delirium, an acutely altered and fluctuating mental status, can present as irritability, combative behaviour, lethargy, and decreased alertness and motor activity; many patients exhibit hypoactive symptoms [11]. PD has been associated with benzodiazepines, propofol, dimenhydrinate and narcotics, which are routinely administered to patients undergoing various surgeries under different anesthetic and analgesic techniques [12,13,14]. Despite the large body of research on this topic, delirium continues to be under recognized [15,16].
Previous studies demonstrated the risk of PD being up to 14.7% even among routine orthopaedic procedures such as hip surgery [17]. As our population ages, there is a larger need for orthopaedic surgery among the elderly [18]. With age being a consistent predictor for PD [1,4,6] we can assume that the incidence and burden of PD will increase if things remain unchanged.
Early PD has major implications in patients’ health as more than 80% of patients with symptoms of delirium in the recovery room were diagnosed with delirium during their hospital stay [19]. Early recognition and management of delirium leads to reduced severity and shortened hospital stays attributed to PD [20].
Currently, there are little data examining the predictors of PD in patients undergoing elective hip and knee arthroplasty, a unique and important population. When the literature separates those undergoing urgent or emergent hip surgery compared to elective patients, there is a significant difference in their incidences of PD [3], supporting further analysis.
The gold standard for a diagnosis of delirium is based on criteria outlined in the Diagnostic and Statistical Manual of Mental Disorders (DSM) [21]. There have been several tools developed to aid in the assessment of delirium such as the Confusion Assessment Method and the Memorial Delirium Assessment Scale, among others. However, these tools have been used by physicians, and those with specific training, and may not be as sensitive and specific as needed. The Nursing Delirium Screening Scale (NuDESC) was developed to address these concerns and provide a readily accessible tool to nursing staff, who are likely to have the most and closest contact with patients postoperatively [22].
The primary objective of this study is to assess the incidence of PD in patients undergoing elective hip and knee arthroplasty using the NuDESC, which was the standard of care at our institution. Secondary objectives included analysis of predictors of PD in this population and determining whether postanesthetic care unit (PACU) (day 0) PD is associated with prolonged recovery room and hospital length of stay.

2. Materials and Methods

2.1. Study Design

Prospective observational study.

2.2. Recruitment

The study and protocol were approved by the Protocol Review Committee and Hamilton Integrated Research Ethics Board. Recruitment occurred among patients presenting for primary elective total hip or knee arthroplasty at the Juravinski Hospital, an academic adult tertiary care centre for orthopaedic surgery in Hamilton, Ontario associated with McMaster University, from October 2015 to October 2017. Patients provided written, informed consent to participate. All cases were primary total joint arthroplasties (hip or knee). Exclusion criteria consisted of repeat surgery on the same hip or knee, preoperative NuDESC score ≥ 2, inability to converse in English, documented history of dementia, severe hearing impairment, prior enrollment in the same study, and need for intensive care unit admission. Age was not a factor in patient selection.

2.3. Sample Size Calculation

This was a prospective observational study. A total sample size of 1000 patients was determined based on previous studies reporting that incidence of early PD for elective surgery is up to 20% [22], and previous analysis simulations showing that 10–15 events per variable would be appropriate for association analyses [23]. A decision was made to limit the list of potential delirium predictors to 10 variables with 15 events per variable being necessary meaning the sample size required as calculated by a biostatistician was approximately 750. To ensure sufficient power to investigate 10 potential predictors of delirium, we rounded up to a sample size of 1000 patients to accommodate a potentially lower incidence of delirium.

2.4. Delirium Assessment

The NuDESC (Appendix A) is a nursing assessment tool used in detecting delirium. It is a five-item scale with each item rated from 0 to 2 depending on the severity of symptoms. Scores of ≥2 have been shown to be both sensitive and specific for detecting delirium in the recovery room relative to the DSM Fourth Edition classification [21,22], and high specificity for the DSM Fifth Edition, which is considered the gold standard for diagnosing delirium [21,24]. Delirium was assessed in the PACU, then twice daily until postoperative day 3, or discharge, whichever came first. This was in accordance with the European Society of Anaesthesiology and Intensive Care Medicine guidelines [25].

2.5. Data Collection

Prior to the study start, nurse educators ensured all preoperative, PACU, and ward nurses were trained on the correct use of NuDESC. Preoperative nurses evaluated all eligible patients using the NuDESC on presentation to the preoperative unit. All anesthesiologists providing care to these patients were blinded to the NuDESC score and instructed to provide routine anesthetic management as per the anesthesiologist’s discretion (hospital standard of care for regional or general anesthetic). Postoperatively, patients were transferred to the PACU where they received routine postoperative care. At 1 h postoperatively or at PACU discharge if less 1 h, the PACU nursing staff, who were blinded to the initial NuDESC assessment, evaluated the patients using the NuDESC. Upon discharge from PACU, patients were transferred to the ward under the orthopedic team. As noted above, ward nurses recorded the patients’ NuDESC score twice daily on postoperative day (POD) 1, 2 and 3, or until discharge, whichever came first. NuDESC assessments were recorded in the patient chart at the above time points. A chart review of all eligible patients was conducted upon discharge to obtain NuDESC data.

2.6. Outcomes

The primary outcome was delirium as diagnosed by a NuDESC score ≥ 2 measured at either 1 h postoperatively or at PACU discharge if the time in PACU was less than 1 h postoperatively. Secondary outcomes included the duration of PACU stay, duration of hospital stay, and NuDESC scores on POD 1, 2, and 3.

2.7. Data Analyses

SAS software Version 9.4 (Cary, NC, USA) was used for all statistical analyses. Demographic characteristics were captured both overall (across all participants) and by delirium status. Continuous variables were described using column means and standard deviations (SD); categorical variables were described using counts and column percentages. The overall incidence of delirium on each day (during PACU and afterwards) was reported using counts, percentages, and corresponding 95% confidence intervals (CI). Potential risk factors of delirium were then explored using unadjusted logistic regression analyses. These risk factors investigated were age (years); sex; body mass index (kg/m2); alcohol consumption (per 1 drink/week); past medical history of: cardiovascular, respiratory, central nervous system, hematologic, musculoskeletal, endocrine and psychiatric disease; smoking status (active, ex-, or non-smoker); history of opioid intake; type of surgery (hip, knee); type of anesthesia (general, regional); whether or not a peripheral nerve block was given; type of intraoperative medication used for general anesthesia (propofol, midazolam, and opioids [fentanyl, sufentanil, hydromorphone, or morphine]); type of intraoperative medication used for regional anesthesia (propofol, midazolam, opioid [fentanyl or sufentanil]); postoperative medication use (morphine, hydromorphone, dimenhydrinate); and American Society of Anesthesiologists (ASA) level. Each type of intraoperative medication for general and regional anesthesia was investigated individually as binary variables. Results of the regression analyses were reported using odds ratios (OR), 95% CIs and p values.
To determine the association between recovery room delirium with (a) prolonged recovery room stay and (b) hospital stay, Mann–Whitney U tests were performed. Results were presented using descriptive statistics (medians and quartiles [Q1 and Q3]) and p values from the statistical tests.

3. Results

Demographics of the sample are presented in Table 1. A total of 978 patients met inclusion criteria, of which 25 (2.56%) had PD (NuDESC scores ≥ 2). The total age range was 24–96 years with a mean (SD) of 66.99 (10.19). Patients who did not experience delirium had a mean age (SD) of 66.74 (10.06) years and mean surgical duration (SD) of 95.51 (28.86) min. Those who experienced delirium had a higher mean (SD) age of 76.23 (10.93) years and similar mean surgical duration (SD) of 94.58 (29.59) min.
When accounting for the cases converted from regional anesthesia to general anesthesia, there was no significant difference in the proportion of cases that received general anesthesia between the delirium and non-delirium groups at 14.18% and 15.38% respectively. There were no cases with an American Society of Anesthesiologists (ASA) class less than III in the delirium cohort while the non-delirium cohort had approximately 20% of its cases with an ASA less than III. The delirium group had 69.23% of its patients receive opioids in the PACU, a significantly larger proportion compared to the non-delirium group at 46.32%. There were no differences in patient weights, heights, duration of surgery or sex.
The overall incidence of delirium (95% CI) was 2.7% (1.7% to 3.9%). As patients were observed each day, the incidence of delirium and corresponding 95% CI in the PACU, POD 1, POD 2, and POD 3 were 0.72% (0.3% to 1.5%), 0.93% (0.4% to 1.8%), 0.62% (0.2% to 1.4%), and 0.42% (0.1% to 1.1%), respectively (Table 2). No incidences of delirium were reported on POD 4 or beyond (Table 2). The incidence of PD at each time point data were collected is presented in Table 3.
The analyses of the potential risk factors of delirium are presented in Table 4. A multivariable analysis could not be performed due to the low incidence of delirium in our sample. Illicit drug use and ASA classification did not have enough observations in each level and were excluded from a regression analysis. History of psychiatric, cardiovascular, and central nervous system disease were found to have increased risk of delirium with significant associations (p < 0.05); ORs (95% CI) were 4.74 (2.10 to 10.70), 3.65 (1.09 to 12.25), and 3.50 (1.53 to 8.03), respectively. Similarly, older age, and a history of hematologic and endocrinologic disease were also significantly associated with delirium, with ORs (95% CI) of 1.69 (1.35 to 2.11), 2.66 (1.09 to 6.45), and 2.27 (1.04 to 4.97) respectively. Postoperative opioid use had an OR (95% CI) of 0.4 (0.17 to 0.89) (p < 0.05), and ASA level had an OR (95% CI) of 2.37 (1.05 to 5.33) (p < 0.04). No significant associations were observed for sex, body mass index (BMI), alcohol consumption, history of respiratory or musculoskeletal disease, smoking status, type of surgery, type of anesthesia, the use of a peripheral nerve block, propofol, midazolam, perioperative opioid use or postoperative dimenhydrinate use.
Overall, the length of stay in recovery room ranged from 0 to 169.3 h; hospital stay ranged from 0 to 46 days. No significant differences were observed among patients with and without delirium in the PACU for each outcome (p > 0.05) (Table 5). The median length of stay in the recovery room (Q1, Q3) for those without delirium was 1.7 h (1.3, 2.3), similar to those with delirium at 1.7 h (1.5, 2.3) (p = 0.705). The median length of hospital stay (Q1, Q3) was 2 days (2, 3) for patients without delirium, and 4 days (1, 13) for patients with delirium (p = 0.216).

4. Discussion

The main goal of this study was to assess incidence of PACU delirium among patients undergoing elective hip and knee arthroplasties.
The incidence of delirium in this sample was 2.7% (1.7% to 3.9%), which is consistent with the wide range of previously reported data using other methods [26,27,28]. This study found that increasing age, ASA > 3, various comorbidities (cardiovascular, central nervous system, hematological, endocrine, and psychiatric) and opioid use in PACU was associated with an increased incidence of PD. In this population of joint replacement patients PD did not lead to a prolonged stay in PACU but it did lead to a longer stay in hospital (although this difference was not statistically significant).
Although data on the incidence and predictors of delirium exist for several surgery types and patient populations [1,3,4,5], there is an absence of data for patients undergoing elective hip and knee arthroplasty. In the literature reporting on hip surgery patients, most of it centres around hip fractures [3,29]. The lower incidence in this study may be attributed to the predominant use of spinal anesthesia in this sample when compared to other studies [30]. Regional anesthesia has been shown to have less of an impact on perioperative cognitive function than general anesthesia in the elderly; however, recent reviews do acknowledge that the generalizability of this effect is limited by the heterogeneity of many studies [31]. In this study, because each anesthesiologist was given the freedom on the administration of anesthesia, their decision may already have been impacted by a desire to reduce the risk for postoperative delirium based on the patient health, medical history, and knowledge about PD leading to a nonbiased allocation of patients. This is supported by the data that show there were no delirious patients with ASA class ≤ 2 suggesting that the anesthesiologists identified patients with a compromised health status and may have altered their anesthetic management to reduce the incidence of PD [29]. The patients who were subject to spinal anesthesia may have already had more compromised overall health making their incidence of delirium more likely regardless of the type of anesthesia used. The allocation of patients to regional or general anesthesia was not random and may have impacted the results.
The incidence of delirium over time in our study remains relatively constant over the measured period. It is possible that patients with a prolonged hospital admission are subject to more triggers for delirium (such as poor sleep or pain) [27] but without more information on this sample there is no definitive conclusion. Furthermore, it is likely that the patients in our sample who had a protracted hospital stay were more medically unwell than the average patient prior to the surgery and this, in and of itself, may be a significant contributor to their propensity for delirium. As delirium has a complex etiology [27] a further subgroup analysis of a larger patient sample may reveal reasons as to why some patients present with delirium several days, and not immediately after their procedure.
Age continues to be an important predictor of PD [32]. Increasing age may be associated with an increased risk of PD through an increase in dementia incidence (which is associated with an increase in PD) [33]. Age may also be associated with frailty, changes in brain architecture, and alterations in pharmacodynamics, all of which have been associated with PD [28]. ASA also continues to be an important predictor of PD, as shown in previous literature [10,28,29]. ASA > 3 reflects poorer overall health status, and these patients may have impaired recovery from surgery [28]
This study supports a statistically significant association of cardiovascular, hematologic, endocrinologic, central nervous system and psychiatric disease as being significant predictors for PD, findings that are consistent with the existing literature [16]. The statistically significant findings of cardiovascular, hematologic and endocrinologic disease are associated with vascular risk factors [34], which can cause a perfusion pressure deficit and lead to a chronic brain hypoperfusion state [35]. These risk factors have been shown to accelerate cognitive decline and increase the risk of dementia [28,29,30]. Despite excluding those with known neurocognitive disease, patients with these features on history may have mild, or undiagnosed dementia that may only be presenting as PD, which is supported by existing data [3]. It is again supported by the higher ASA class status of the delirium patients. If the PD captured by this study is a sequalae of hypoperfusion, then more aggressive perioperative blood pressure management may lead to its reduction. Data regarding this conclusion exist [27,36,37] and support the need for further research into this hypothesis, specifically in this population. Perioperative blood pressure of this sample may reveal an association in this patient population. These risk factors for PD are similar to those found in a recent large, patient-level meta-analysis: increasing age, ASA 3 or 4, low BMI, history of delirium and the absence of a college degree (or higher) [32]. Similarly to a recent meta-analysis involving 34 RCTs and over 3400 patients, intraoperative benzodiazepine did not increase the incidence of PD [38].
Delirium presenting immediately after surgery, and on the days following, is consistent with the fluctuating course of the disease. Strategies for addressing delirium are well discussed and can be easily implemented by healthcare staff looking after affected patients [27]. This may be supported by the finding that the presence of delirium in the PACU was not associated with an increased length of stay in the PACU nor the hospital, suggesting that when delirium was detected it was either self-limited, or corrected. This finding, however, would need to be further investigated with a larger sample size. Although postoperative opioid use specifically demonstrated a statistically significant relation with decreased delirium, the exact mechanism is unclear. Opioids as well as pain, are both triggers for delirium [3]. The literature has demonstrated that a judicious use of some opioids may improve postoperative delirium by treating the pain that may be driving the delirium [39,40]. As the research protocol did not illustrate a temporal relationship between NuDESC assessments and the administration of opioids, no conclusions about the mechanism can be drawn from our study. Research into the specific actions of nurses in response to this sample in the PACU, and comparisons to other surgical groups, such as those undergoing emergent hip or knee surgery, may further shed light on the underlying etiology of delirium in these patients. The analysis presented does not compare presence of delirium after the PACU to length of stay; these data may speak to broader trends on the impact of delirium to hospital length of stay.
The strength of our study is that it represents a large sample of patients who had complete baseline data and postoperative delirium assessments. A weakness of our study is the low incidence of PD, which give us less ability to identify potential risk factors. The NuDESC is a validated and highly specific assessment tool for delirium, and has been found to be at least as, if not more sensitive, than other tools [21,22]. Our lower incidence of delirium may potentially have been because of NuDESC’s lower sensitivity to diagnosing hypoactive and mixed delirium [24] but as we did not use a second delirium tool no direct conclusions can be drawn. The existing literature examines strategies for increasing its sensitivity quite well [23]; future work may require additional analysis of the NuDESC itself with comparisons to other well-validated delirium assessment tools to determine its true efficacy in detecting PD in this population.
The low incidence of delirium in our sample limited our analyses. Since only 26 patients exhibited delirium, a multivariable analysis could not be performed. Further, this was a single-center study in a large tertiary academic center and may not be generalizable to other settings. However, these elective procedures are commonly performed and the large sample size may have mitigated this limitation.

5. Conclusions

When examining patients undergoing elective hip and knee surgeries PD continues to play a significant role in their care. Age; cardiovascular, hematologic, endocrinologic, central nervous system, and psychiatric disease; postoperative opioid use; and ASA level may be associated with PD in this patient group. The only identified risk factor in this study that could potentially be modified would be postoperative opioid management; however, this factor is difficult to modify. Further work looking at the appropriate detection of delirium at the nursing level in the PACU, and further study of a broader range of risk factors may shed light onto the true incidence of delirium in these patients, and interventions that may mitigate delirium incidence. Additionally, a larger, multicenter study may better elucidate the incidence of delirium in this patient population and allow adjusted multivariable regression analysis.

Author Contributions

Conceptualization, J.P.; methodology, L.T.; formal analysis, T.V.; investigation, A.H., H.K.M. and T.K.; data curation, A.H., H.K.M. and T.K.; writing—original draft preparation, J.P.; writing—review and editing, J.P., A.H., H.K.M. and T.K.; supervision, J.P.; project administration, J.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki, and approved by the McMaster University Protocol Review Committee and Hamilton Integrated Research Ethics Board (protocol code 0014, 29 October 2015).

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

Author Thuva Vanniyasingam was employed by the company Cytel. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Appendix A. The Nursing Delirium Screening Scale

Features and DescriptionsSymptom Rating (0–2)
SymptomMidnight–8 a.m.8 a.m.–4 p.m.4 p.m.–Midnight
I. Disorientation
Verbal or behavioral manifestation of not being oriented to time or place or misperceiving persons in the environment
II. Inappropriate behavior
Behavior inappropriate to place and/or for the person; e.g., pulling at tubes or dressings, attempting to get out of bed when that is contraindicated, and the like.
III. Inappropriate communication
Communication inappropriate to place and/or for the person; e.g., incoherence, noncommunicativeness, nonsensical or unintelligible speech.
IV. Illusions/Hallucinations
Seeing or hearing things that are not there; distortions of visual objects.
V. Psychomotor retardation
Delayed responsiveness, few or no spontaneous actions/words; e.g., when the patient is prodded, reaction is deferred and/or the patient is unarousable.
Total score
Gaudreau JD, Gagnon P, Harel F, Tremblay A, Roy MA. Fast, systematic, and continuous delirium assessment in hospitalized patients: the nursing delirium screening scale. J Pain Symptom Manage. 2005;29(4):368–75 [22].

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Table 1. Demographics of patient sample.
Table 1. Demographics of patient sample.
DemographicsNo Delirium (n = 952)Delirium (n = 25)Overall
(n = 978)
Age (years); mean (SD)66.74 (10.06)76.23 (10.93)66.99 (10.19)
Missing1.1
Weight (kg); mean (SD)89.54 (20.03)83.19 (19.28)89.37 (20.02)
Missing6 6
Height (cm); mean (SD)167.07 (10.64)163.22 (9.58)166.97 (10.63)
Missing8210
Duration of surgery (min); mean (SD)95.51 (28.86)94.58 (29.59)95.48 (28.86)
Sex, n (%)
Male410 (43.1)12 (46.2)422 (43.2)
Female542 (56.9)14 (53.8)556 (56.9)
Surgery type; n (%)
Knee537 (56.4)11 (42)548 (56.0)
Hip415 (43.6)15 (58)430 (44.0)
Anesthesia type; n (%)
General 105 (11.0)4 (15)109 (11.2)
Regional817 (85.8)22 (85)839 (85.8)
Regional converted to general30 (3.2)030 (3.1)
Peripheral nerve block; n (%)79 (8.6)1 (4)80 (8.5)
Missing31 31
Intraoperative medications 1; n (%)
•  General anesthesia
Propofol119 (12.5)3 (12)122 (12.5)
Midazolam54 (5.7)2 (8)56 (5.7)
Opioids (Fentanyl, Sufentanil, Hydromorphone, Morphine)109 (11.5)4 (15)113 (11.6)
•  Regional anesthesia
Propofol758 (79.6)17 (65)775 (79.2)
Midazolam604 (63.5)14 (54)618 (63.2)
Opioids (Fentanyl, Sufentanil) 2260 (27.3)9 (35)269 (27.5)
Medication used in PACU; n (%)
Opioid (includes Morphine, Hydromorphone)441 (46.3)18 (69)459 (46.9)
Dimenhydrinate44 (4.6)2 (8)46 (4.7)
ASA Level; n (%)
112 (1.3)012 (1.2)
2199 (21.1)0199 (20.5)
3581 (61.5)16 (62)597 (61.5)
4153 (16.2)10 (39)163 (16.8)
Missing7 7
1 All intraoperative medications were analyzed independently (presence/absence of each), so the proportions will not add to 100%; 2 Opioids administered intravenously in addition to the opioids administered for regional anesthesia at the attending anesthesiologists’ discretion. ASA, American Society of Anesthesiologists; PACU, postanesthetic care unit; SD, standard deviation.
Table 2. Incidence of delirium according to day.
Table 2. Incidence of delirium according to day.
n/NIncidence (95% CI)
PACU(7/978)0.72% (0.3% to 1.5%)
POD 1(9/971)0.93% (0.4% to 1.8%)
POD 2(6/962)0.62% (0.2% to 1.4%)
POD 3(4/956)0.42% (0.1% to 1.1%)
CI, confidence interval; PACU, postanesthetic care unit; POD, postoperative day.
Table 3. Incidence of delirium at each time point.
Table 3. Incidence of delirium at each time point.
Postoperative DayN = 39
POD0 (PACU)7 (17.9)
POD1 a.m.3 (7.7)
POD1 p.m.8 (20.5)
POD2 a.m.3 (7.7)
POD2 p.m.7 (17.9)
POD3 a.m.6 (15.4)
POD3 p.m.5 (12.8)
PACU, postanesthetic care unit; POD, postoperative day.
Table 4. Investigation of potential risk factors of delirium.
Table 4. Investigation of potential risk factors of delirium.
PredictorOR (95% CI)p
Age (change in 5 years)1.69 (1.35 to 2.11)<0.01
Female0.88 (0.40 to 1.93)0.75
BMI (change in 5 kg/m2)0.95 (0.69 to 1.31)0.77
Alcohol consumption (OR determined for change in 1 drink/week)0.61 (0.27 to 1.41)0.25
Past medical history of…
  Cardiovascular disease3.65 (1.09 to 12.25)0.04
  Respiratory disease0.76 (0.33 to 1.77)0.53
  Central nervous system disease3.50 (1.53 to 8.03)<0.01
  Hematologic disease2.66 (1.09 to 6.45)0.03
  Musculoskeletal disease0.54 (0.16 to 1.86)0.33
  Endocrinologic disease2.27 (1.04 to 4.97)0.04
  Psychiatric disease4.74 (2.10 to 10.70)<0.01
Smoking status
  Active smoker0.87 (0.19 to 3.94)0.92
  Ex-smoker0.89 (0.38 to 2.11)0.93
  Non-smokerReference 4.
Opioid use at time of surgery1.71 (0.75 to 3.90)0.2
Type of surgery
  Hip arthroplasty1.77 (0.80 to 3.88)0.16
  Knee arthroplastyReference 4
Type of anesthesia
  Regional0.91 (0.31 to 2.68)0.86
  General 1Reference 4
Peripheral nerve block0.4 (0.06 to 3.19)0.41
Intraoperative medications
  General anesthesia
•  Propofol 0.91 (0.27 to 3.09)0.88
•  Midazolam 1.38 (0.32 to 6.02)0.66
•  Opioids (Fentanyl, Sufentanil, Hydromorphone, or Morphine) 1.41 (0.48 to 4.16)0.54
  Regional anesthesia
•  Propofol 0.48 (0.21 to 1.1)0.08
•  Midazolam 0.67 (0.31 to 1.47)0.32
•  Opioids (Fentanyl or Sufentanil) 21.41 (0.62 to 3.2)0.41
Postoperative medications 3
Opioids (Morphine or Hydromorphone)0.4 (0.17 to 0.89)0.03
Dimenhydrinate (mg)1.7 (0.39 to 7.51)0.47
ASA level
•   4 2.37 (1.05 to 5.33)0.04
•   3Reference
1 Also includes individuals with regional anesthesia converted to general anesthesia; 2 Opioids administered intravenously in addition to the opioids administered for regional anesthesia at the attending anesthesiologists’ discretion; 3 Opioid use while in hospital. ASA, American Society of Anesthesiologists; BMI, body mass index; CI confidence interval; OR, odds ratio; 4 What the risk factors are compared to.
Table 5. Relationship between ‘length of stay in recovery room’ and ‘hospital stay’ with PACU (Day 0) delirium.
Table 5. Relationship between ‘length of stay in recovery room’ and ‘hospital stay’ with PACU (Day 0) delirium.
OutcomesNo PACU Delirium (n = 948)PACU Delirium (n = 7)p
Length of Stay in recovery room (hours); median (Q1, Q3)1.7 (1.3, 2.3)1.7 (1.5, 2.3)0.705
Missing23
Hospital stay (days); median (Q1, Q3)2 (2, 3)4 (1, 13)0.216
Missing3
PACU, postanesthetic care unit.
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Paul, J.; Hamid, A.; Ma, H.K.; Kim, T.; Thabane, L.; Vanniyasingam, T. Incidence and Predictors of Postoperative Delirium in Patients Undergoing Elective Hip and Knee Arthroplasty: A Prospective Observational Study. Anesth. Res. 2025, 2, 11. https://doi.org/10.3390/anesthres2020011

AMA Style

Paul J, Hamid A, Ma HK, Kim T, Thabane L, Vanniyasingam T. Incidence and Predictors of Postoperative Delirium in Patients Undergoing Elective Hip and Knee Arthroplasty: A Prospective Observational Study. Anesthesia Research. 2025; 2(2):11. https://doi.org/10.3390/anesthres2020011

Chicago/Turabian Style

Paul, James, Amir Hamid, Heung Kan Ma, Thomas Kim, Lehana Thabane, and Thuva Vanniyasingam. 2025. "Incidence and Predictors of Postoperative Delirium in Patients Undergoing Elective Hip and Knee Arthroplasty: A Prospective Observational Study" Anesthesia Research 2, no. 2: 11. https://doi.org/10.3390/anesthres2020011

APA Style

Paul, J., Hamid, A., Ma, H. K., Kim, T., Thabane, L., & Vanniyasingam, T. (2025). Incidence and Predictors of Postoperative Delirium in Patients Undergoing Elective Hip and Knee Arthroplasty: A Prospective Observational Study. Anesthesia Research, 2(2), 11. https://doi.org/10.3390/anesthres2020011

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