Background

The effect of delirium on physical function in patients undergoing noncardiac thoracic surgery has not been well described and may differ from that in other surgical populations.

Objective

To determine the effects of delirium on muscle strength and functional independence. The primary end point was change in Medical Research Council sum score (MRC-SS) by delirium status.

Methods

A secondary analysis of data from a clinical trial involving English-speaking adults aged 18 years or older who were undergoing major noncardiac thoracic surgery. Exclusion criteria were history of schizophrenia, Parkinson disease, dementia, alcohol abuse, or neuroleptic malignant syndrome; haloperidol allergy; being pregnant or nursing; QT prolongation; and taking levodopa or cholinesterase inhibitors. Delirium was assessed twice daily using the Confusion Assessment Method for the Intensive Care Unit. Preoperatively and postoperatively, muscle strength was assessed using the modified MRC-SS and functional independence was assessed using the Katz scale of activities of daily living. Changes in MRC-SS and Katz score by delirium status were analyzed using the Fisher exact test.

Results

Seventy-three patients were included in the analysis. Median (interquartile range) MRC-SS and Katz score before surgery did not differ significantly between patients without and with delirium (MRC-SS: 30 [30-30] vs 30 [30-30], P > .99; Katz score: 6 [6-6] vs 6 [6-6], P = .63). The percentage of patients with a change in MRC-SS was similar in patients without and with delirium (17% vs 13%, respectively; P > .99). More patients in the delirium group had a change in Katz score (13% vs 0%, P = .04).

Conclusions

Postoperative delirium was not associated with change in muscle strength. Follow-up studies using other muscle measures may be needed.

Delirium occurs in nearly 50% of patients undergoing noncardiac thoracic surgery.1-3  In cardiac surgery patients, delirium is associated with decreased physical function, increasing the risk of institutionalization.4  Patients experiencing postoperative delirium after transcatheter or surgical aortic valve replacement had decreased physical function at 1 month.5  In cardiac surgery, long periods of cardiopulmonary bypass, arterial hypotension, and low cardiac output may increase the risk of postoperative delirium.6  The effect of delirium on muscle strength and physical function in noncardiac thoracic surgery patients, however, has not been well described. We hypothesized that this effect might differ from that in cardiac surgery patients because of differences in anesthesia and surgical technique (eg, lack of cardiopulmonary bypass).7 

Objective

The objective of this study was to determine the effect of delirium on muscle strength and functional independence in patients undergoing noncardiac major thoracic surgery. The primary endpoint was change in Medical Research Council sum score (MRC-SS) by delirium status. A secondary endpoint was change in score on the Katz scale of activities of daily living (ADLs) by delirium status.

The aim of this study was to measure the effect of postoperative delirium on muscle strength and functional independence.

Methods

Study Design

We conducted a secondary analysis of data from a previously reported randomized controlled trial comparing scheduled low-dose haloperidol versus placebo for prevention of delirium in patients who had undergone major noncardiac thoracic surgery.2  The study was conducted at a tertiary care center from September 2013 to December 2015 and was approved by the Indiana University institutional review board.

Eligibility Criteria

The parent trial involved English-speaking adults aged 18 years or older who were undergoing major noncardiac thoracic surgery. Patients were excluded from the parent trial if they had a history of schizophrenia, Parkinson disease, dementia, alcohol abuse, or neuroleptic malignant syndrome or had an allergy to haloperidol. Patients who were pregnant or nursing, had QT prolongation of over 500 milliseconds, or were taking levodopa or cholinesterase inhibitors were also excluded. For the current analysis, we excluded patients who did not have both preoperative and postoperative MRC and Katz assessments completed.

Outcome Measures

The primary outcome of this analysis was change in MRC-SS by delirium status. We also examined change in Katz score by delirium status.

Medical Research Council Sum Score

Global muscle strength was assessed by using a modified MRC-SS both preoperatively and postoperatively.8  The MRC-SS has high interrater reliability (κ = 0.77-0.88) and intrarater reliability (Spearman rs = 0.78).9 

The MRC-SS was used to grade muscle strength from 0 to 5 (with 0 indicating paralysis, 3 indicating movement against gravity over near-full range of motion, and 5 indicating normal power) in the following muscle groups: shoulder abduction, elbow flexion, wrist extension, hip flexion, knee extension, and ankle dorsiflexion. We used a modified MRC-SS with strength assessed on one-half of the body, with a maximum possible score of 30 (the nonmodified MRC-SS maximum is 60). These assessments were repeated at the time of hospital discharge. A modified MRC-SS was used because all patients were high functioning and ambulatory at baseline, and the baseline assessments occurred in the time-constrained preoperative period.

Katz Scale of Activities of Daily Living

Activities of daily living were assessed by using the Katz scale both preoperatively and postoperatively. The Katz scale is a widely used 6-item self-report tool to assess functional capacity and independence in performing ADLs.10  The scale assesses independence in bathing, dressing, toileting, transferring, continence, and feeding, with higher scores indicating better function. Scores range from 0 (very dependent) to 6 (fully independent). The Katz scale has high content validity even in patients with neurologic decline, and lower Katz scores were predictive of adverse events in cardiovascular patients undergoing transcatheter valve replacements.11,12 

Delirium Measures

Level of sedation was assessed twice daily using the Richmond Agitation-Sedation Scale (RASS), and delirium was assessed using the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU).13  The RASS has excellent interrater reliability (interclass correlation coefficient = 0.956, κ = 0.73, 95% CI = 0.71-0.75).13  The CAM-ICU is a highly sensitive and specific instrument that has been validated in the hospital setting (sensitivity = 97%, specificity = 98%, accuracy = 98.4%). The CAM-ICU also has high interrater reliability (κ = 0.96, 95% CI = 0.92-0.99).14  Delirium was defined as any positive assessment using the CAM-ICU.

Other Data Collection

Participant demographic and clinical data were collected from the electronic medical records. Information was collected on demographic characteristics, chronic comorbidities as determined with the Charlson Comorbidity Index, and American Society of Anesthesiologists classification of fitness before surgery.15 

Statistical Analysis

The outcomes of interest were change in MRC-SS and change in Katz score by delirium status. Descriptive statistics were analyzed as mean and SD or median and interquartile range (IQR), as appropriate, for continuous variables and proportions for categorical variables. The t test or the Wilcoxon rank sum test was used to assess differences for continuous variables between groups, whereas the χ2 test or the Fisher exact test was used to assess differences for categorical variables. We imputed missing MRC-SS and Katz subscales from the person-specific mean of nonmissing items if 50% or fewer of the items were missing. Changes in MRC-SS and Katz score by delirium status were analyzed by using the Fisher exact test. All data analyses were performed using SAS version 9.4.

Results

A total of 73 patients were included in the analysis. Baseline characteristics are shown in the Table. Mean (SD) age in the sample population was 61.1 (12.7) years, 99% of participants were white, and 27% were female. Fifteen patients (21%) experienced delirium. The delirium group had significantly longer median (IQR) stays (in days) in the hospital (10 [9-10] vs 7 [6-10], P = .04) and the ICU (3 [2-6] vs 2 [1-3], P = .01). Patients in the delirium group had a longer mean (SD) duration of surgery in minutes (272.1 [86.9] vs 211.9 [92.3], P = .03).

Patients had high muscle strength and functional independence preoperatively. No significant differences were found at baseline between those without and with delirium in median (IQR) MRC-SS (30 [30-30] vs 30 [30-30], respectively; P > .99) or Katz score (6 [6-6] vs 6 [6-6], respectively; P = .63). There was no significant difference between patients without and with delirium in percentage of patients with a change in MRC-SS (17% vs 13%, respectively; P > .99). A subgroup analysis of the esophagectomy patients did not alter the findings. As shown in the Table, there was a significant difference between patients without and with delirium in mean (SD) postoperative Katz score (6 [0] vs 5.3 [1.8], respectively, P = .005). A larger percentage of patients in the delirium group had a change in Katz score (13% vs 0%, P = .04).

Muscle strength was measured using the modified MRC sum score.

Discussion

In this study, we did not find a significant difference between groups in the percentage of patients with a change in MRC-SS after major noncardiac thoracic surgery, despite a high incidence of delirium in esophagectomy patients. These results may have been due to participants’ good muscle strength and functional independence at baseline and their candidacy for surgery. We did, however, find postoperative delirium to be associated with a change in Katz score for ADLs, consistent with previous studies involving other surgical populations.

In studies of patients after aortic valve surgery and older nonsurgical patients admitted to the hospital, delirium was associated with increased risk of institutionalization after hospital discharge and the need for rehabilitation.4,5  These findings may be due to the patients with delirium having a higher likelihood of treatment with antipsychotics or psychotropic medications, increased use of restraints resulting in immobility, or greater metabolic derangements hindering their recovery.16  We hypothesized that delirium’s negative effects on muscle strength could be the driver of loss of functional independence, but our study results do not confirm this hypothesis.

Patients with delirium may have perceived an impairment in their functional status.

Our findings may be explained by the brief duration of delirium in the study sample, the occurrence of muscle strength assessment before hospital discharge, and the small sample size. In addition, whereas the MRC-SS is objectively measured, the Katz score is self-reported. The subjective decrement in Katz score among delirious patients could be driven by the delirium experience or the longer ICU or hospital stay. Our study also highlights the value of selection of highly functional candidates for surgery, as high baseline strength and functional independence may prevent a decrease in muscle strength despite postoperative delirium.

Strengths of our study include analysis of a non-cardiac surgical population, robust methodological design with use of a well-validated measure of muscle strength, and twice-daily delirium assessments. Our study has several limitations. First, the sample size was small. As this was a secondary analysis of a randomized controlled trial, the sample size was not based on prespecified changes in MRC-SS. Second, time points for postoperative assessments were limited to the hospital stay. With a median hospital stay of 8 days, the Katz score may not have been sensitive to small changes in functional status. Third, the Katz scale may have limited sensitivity in patients with good baseline function.17  Finally, compared with an analog scale, the MRC-SS may be less accurate in detecting weakness in strong, bulky muscles.18 

Our findings add to the existing evidence on the relationship among delirium, reduced muscle strength, and increased risk of institutionalization after discharge. Further studies are needed to better describe effects of delirium on muscle function and return to independence.

REFERENCES

REFERENCES
1
Takeuchi
M
,
Takeuchi
H
,
Fujisawa
D
, et al
.
Incidence and risk factors of postoperative delirium in patients with esophageal cancer
.
Ann Surg Oncol
.
2012
;
19
(
12
):
3963
3970
.
2
Khan
BA
,
Perkins
AJ
,
Campbell
NL
, et al
.
Preventing postoperative delirium after major noncardiac thoracic surgery— a randomized clinical trial
.
J Am Geriatr Soc
.
2018
;
66
(
12
):
2289
2297
.
3
Shaun
OK
,
John
L
.
The prognostic significance of delirium in older hospital patients
.
J Am Geriatr Soc
.
1997
;
45
(
2
):
174
178
.
4
Rudolph
JL
,
Inouye
SK
,
Jones
RN
, et al
.
Delirium: an independent predictor of functional decline after cardiac surgery
.
J Am Geriatr Soc
.
2010
;
58
(
4
):
643
649
.
5
Eide
LS
,
Ranhoff
AH
,
Fridlund
B
, et al
.
Delirium as a predictor of physical and cognitive function in individuals aged 80 and older after transcatheter aortic valve implantation or surgical aortic valve replacement
.
J Am Geriatr Soc
.
2016
;
64
(
6
):
1178
1186
.
6
Gottesman
RF
,
Grega
MA
,
Bailey
MM
, et al
.
Delirium after coronary artery bypass graft surgery and late mortality
.
Ann Neurol
.
2010
;
67
(
3
):
338
344
.
7
Hudetz
JA
,
Iqbal
Z
,
Gandhi
SD
,
Patterson
KM
,
Byrne
AJ
,
Pagel
PS
.
Postoperative delirium and short-term cognitive dysfunction occur more frequently in patients undergoing valve surgery with or without coronary artery bypass graft surgery compared with coronary artery bypass graft surgery alone: results of a pilot study
.
J Cardiothorac Vasc Anesth
.
2011
;
25
(
5
):
811
816
.
8
Hough
CL
,
Lieu
BK
,
Caldwell
ES
.
Manual muscle strength testing of critically ill patients: feasibility and interobserver agreement
.
Crit Care
.
2011
;
15
(
1
):
R43
. doi:.
9
Paternostro-Sluga
T
,
Grim-Stieger
M
,
Posch
M
, et al
.
Reliability and validity of the Medical Research Council (MRC) scale and a modified scale for testing muscle strength in patients with radial palsy
.
J Rehabil Med
.
2008
;
40
(
8
):
665
671
.
10
Katz
S
,
Ford
AB
,
Moskowitz
RW
,
Jackson
BA
,
Jaffe
MW
.
Studies of illness in the aged. The index of ADL: a standardized measure of biological and psychosocial function
.
JAMA
.
1963
;
185
:
914
919
.
11
Ferretti-Rebustini
RE
,
Balbinotti
MA
,
Jacob-Filho
W
, et al
.
Validity of the Katz Index to assess activities of daily living by informants in neuropathological studies
.
Rev Esc Enferm USP
.
2015
;
49
(
6
):
946
952
.
12
Puls
M
,
Sobisiak
B
,
Bleckmann
A
, et al
.
Impact of frailty on short- and long-term morbidity and mortality after trans-catheter aortic valve implantation: risk assessment by Katz Index of activities of daily living
.
EuroIntervention
.
2014
;
10
(
5
):
609
619
.
13
Sessler
CN
,
Gosnell
MS
,
Grap
MJ
, et al
.
The Richmond Agitation-Sedation Scale: validity and reliability in adult intensive care unit patients
.
Am J Respir Crit Care Med
.
2002
;
166
(
10
):
1338
1344
.
14
Ely
EW
,
Margolin
R
,
Francis
J
, et al
.
Evaluation of delirium in critically ill patients: validation of the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU)
.
Crit Care Med
.
2001
;
29
(
7
):
1370
1379
.
15
Charlson
ME
,
Sax
FL
,
MacKenzie
CR
,
Fields
SD
,
Braham
RL
,
Douglas
RG
Jr
Assessing illness severity: does clinical judgment work?
J Chronic Dis
1986
;
39
(
6
):
439
452
.
16
Brummel
NE
,
Balas
MC
,
Morandi
A
,
Ferrante
LE
,
Gill
TM
,
Ely
EW
.
Understanding and reducing disability in older adults following critical illness
.
Crit Care Med
.
2015
;
43
(
6
):
1265
1275
.
17
Rudolph
JL
,
Marcantonio
ER
.
Postoperative delirium: acute change with long-term implications
.
Anesth Analg
.
2011
;
112
(
5
):
1202
1211
.
18
John
J
.
Grading of muscle power: comparison of MRC and analogue scales by physiotherapists
.
Int J Rehabil Res
.
1984
;
7
(
2
):
173
181
.

Footnotes

FINANCIAL DISCLOSURES

Dr S Khan is supported by the National Heart, Lung, and Blood Institute (5T32HL091816-07). Dr B Khan is supported by the National Institute on Aging (K23-AG043476). The study was supported by Indiana University Health Values Fund grant VFR-398.

To purchase electronic or print reprints, contact American Association of Critical-Care Nurses, 101 Columbia, Aliso Viejo, CA 92656. Phone, (800) 899-1712 or (949) 362-2050 (ext 532); fax, (949) 362-2049; email, reprints@aacn.org.