Abstract
Objective
To assess the associations of baseline skeletal muscle mass index (SMI) with adverse events and rehabilitation outcomes in patients admitted for rehabilitation.
Design
A retrospective cohort study.
Participants
The subjects were 409 patients (mean age, 79 years; men, 167 [41%]) undergoing rehabilitation because of neurologic disease, musculoskeletal disorders, or hospital-associated deconditioning. Patients were divided into 2 groups according to the definition of sarcopenia by the Asian Working Group for Sarcopenia: those with low SMI (<7.0 kg/m2 in men and <5.7 kg/m2 in women) and those with high SMI (≥7.0 kg/m2 in men and ≥5.7 kg/m2 in women).
Interventions
Not applicable.
Main Outcome Measures
The primary outcomes were adverse events including death and acute illness requiring transfer to other hospitals for specialized treatments. The secondary outcomes were rehabilitation outcomes including the efficiency scores (changes in functional independence measure [FIM] score divided by length of stay) of FIM for motor function (FIM-M) and FIM for cognitive function (FIM-C).
Results
Of the 409 patients, 299 (73%) had a low SMI. The adjusted hazard ratio (95% confidence interval) of the low SMI group relative to the high SMI group for adverse events was 2.79 (1.06-7.34). There were no significant differences between the 2 groups in FIM-M efficiency scores [mean ± SD, low SMI group: 0.4 (0.58) vs high SMI group: 0.47 (0.54), P=.3] and FIM-C efficiency scores [mean ± SD, 0.05 (0.14) vs 0.06 (0.2), P=.4]. Multiple linear regression models did not show significant associations between the low SMI group and FIM-M efficiency or FIM-C efficiency scores (β=0.064, P=.3; β=−0.05, P=.4, respectively).
Conclusion
Low baseline SMI was significantly associated with adverse events but not with rehabilitation outcomes in patients undergoing rehabilitation.
KEYWORDS: Activities of daily living, Adverse events, Functional independence measure, Length of stay, Rehabilitation, Skeletal muscle mass index
Sarcopenia is an age-related syndrome of progressive loss of strength and muscle mass.1, 2, 3, 4, 5 Measurement of skeletal muscle mass and strength and gait speed is essential for the diagnosis of sarcopenia.6 Sarcopenia is associated with adverse health outcomes such as aspiration pneumonia, chronic obstructive pulmonary disease, heart failure, cardio-cerebrovascular disease, and mortality.1, 2, 3, 4, 5 Although many patients admitted to a rehabilitation ward have low skeletal muscle mass, no studies have reported an association between low skeletal muscle mass and adverse events.6
The assessment of muscle parameters, including muscle mass, muscle quality, and muscle strength, is important to determine achievement of rehabilitation.7 The skeletal muscle mass index (SMI), which is used to diagnose sarcopenia, has recently been reported to be related to both motor and cognitive function.6,8 Although devices used for the measurement of SMI are becoming widely available, they are not yet used routinely in rehabilitation assessment.6 Even if SMI can be measured, muscle strength and gait speed may not be able to be measured due to functional impairment, making it impossible to diagnose sarcopenia.6
In Japan, patients who are treated in acute care hospitals and who show functional impairment at discharge are admitted to rehabilitation wards to improve their activities of daily living (ADLs) in both motor and cognitive domains.6 Efficient rehabilitation must be provided to patients within the maximum 180-day hospital stay limit, and rehabilitation efficiency is often expressed as a score of improvement in ADLs divided by the number of hospital days.6 Although several studies have assessed factors associated with improvement in ADLs, the association between SMI and ADLs improvement is uncertain.6,9 Elucidating the effect of SMI on the improvement of patients’ ADLs after acute care is a global challenge, and not only a challenge in Japan.
Regardless of whether sarcopenia can be diagnosed or not, if the baseline SMI before rehabilitation can predict adverse events and the improvement in ADLs in patients undergoing rehabilitation, a more individualized rehabilitation program could be proposed according to the patient's condition. Therefore, in this study, we examined the association of baseline SMI with adverse events and improvement in ADLs in patients admitted to a rehabilitation ward.
Methods
Participants
We conducted a retrospective cohort study of patients hospitalized at the rehabilitation unit of Toyonaka Heisei Hospital in Japan from April 2019 to March 2021. Patients hospitalized because of neurologic diseases, musculoskeletal disorders, or hospital-associated deconditioning, who are eligible for rehabilitation under the public medical insurance system, were included. Exclusion criteria included only the lack of measurement of baseline SMI within 48 hours of admission to the rehabilitation ward and did not include demographic or health issues.6 The participants were followed until discharge, death, or transfer to other hospitals to receive specialized treatments for their acute illness. Patients who died during hospitalization in the rehabilitation ward and those transferred to other hospitals were eliminated from the analyses of secondary outcomes.
Of the 428 patients screened for eligibility, 409 patients met the inclusion criteria and 19 patients without baseline SMI data were excluded (fig 1). The 19 excluded patients did not have baseline SMI data because they had an implanted pacemaker or they failed to remain at rest during measurement of SMI. Patients were divided into 2 groups according to the definition of sarcopenia by the Asian Working Group for Sarcopenia: patients with a low baseline SMI (<7.0 kg/m2 in men and <5.7 kg/m2 in women) and patients with a high baseline SMI (≥7.0 kg/m2 in men and ≥5.7 kg/m2 in women).6
Fig 1.
Study flowchart.
Rehabilitation
Rehabilitation was provided based on the guidelines of the public medical insurance system.6 Individual rehabilitation consisted of 20-minute units and was administered daily.6 Patients with neurologic diseases received 9 units of physical, occupational, and speech therapy per day for a maximum of 150 days (180 days for patients with higher brain dysfunction [HBD]).6 Patients with musculoskeletal disorders were provided 6 units of physical, occupational, and speech therapy per day for a maximum of 90 days.6 Patients with hospital-associated deconditioning underwent 6 units of physical, occupational, and speech therapy per day for a maximum of 90 days.6 In the 6 or 9 units of rehabilitation per day, therapies tailored to the individual patient's disability, such as muscle strengthening training, gait training, training for HBD, and swallowing training, were implemented.
Data collection
The following baseline data were collected through hospital charts: age, men, body mass index (BMI), handgrip strength, the revised Hasegawa's Dementia Scale score (HDS-R), disease category including neurologic disease with or without HBD, musculoskeletal disorders, and hospital-associated deconditioning, comorbidities such as chronic heart failure and chronic respiratory disease, laboratory findings including blood hemoglobin, creatinine, blood urea nitrogen, serum total protein, and serum albumin levels, tube feeding, urinary catheter use, mobility aids, and functional independence measure (FIM). To assess performance of ADLs, patient FIM scores were evaluated within 48 h of admission and within 48 h prior to discharge.6 The FIM consists of 13 items in the motor domain (FIM-M) and 5 items in the cognitive domain (FIM-C) to evaluate a patient's level of independency in ADLs.6 Each item is graded on a scale of 1 (full care required) to 7 (completely independent), with higher scores indicating less need for care.6 The FIM-M score was obtained by adding the scores of the 13 items in the motor domain, and the FIM-C score was obtained by adding the scores of the 5 items in the cognitive domain.
Skeletal muscle mass was assessed with patients in the supine position using bioelectrical impedance analysis (InBody S10, InBody, Japan) within 48 hours after admission and before rehabilitation exercises were started in order to avoid the influence of rehabilitation. Skeletal muscle mass was not measured in patients who had an implanted pacemaker nor in patients who were unable to remain at rest during the measurement.6,10 SMI was calculated as follows:
SMI = appendicular muscle mass (kg)/square of height (m2).6,10
Outcomes
The primary outcomes in this study were adverse events including death and acute illness requiring transfer to other hospitals for specialized treatments. Sarcopenia has been reported to be associated with adverse health outcomes such as aspiration pneumonia, heart failure, and cardio-cerebrovascular disease, all of which were associated with death.1, 2, 3, 4, 5 Therefore, death included all-cause death regardless of the cause of death in this study.
We evaluated the secondary outcomes in patients who completed the rehabilitation program without adverse events, and such outcomes included length of stay, changes in the FIM-M and FIM-C scores (the FIM score on admission was subtracted from the FIM score at discharge), and FIM-M and FIM-C efficiency scores (change in the FIM score/length of stay).11
Statistical analysis
Clinical characteristics and outcomes were analyzed between the 2 groups. Categorical variables were presented as frequencies and percentages and continuous variables were presented as mean (standard deviation [SD]) or as median (interquartile range [IQR]) based on their distribution. Chi-squared test was used to compare categorical variables, and the Student t test or Wilcoxon rank-sum test was used for comparisons of continuous variables. The numbers of missing values were reported, but the imputation of missing values was not conducted to accurately represent the clinical status.
In the analysis of primary outcomes, the incidence of adverse events was stratified by group and assessed with cases per 1000 patient-days. We evaluated cumulative incidence using the Kaplan–Meier method. Intergroup difference was assessed using the log-rank test. Cox proportional hazard models were used to assess the effects of outcomes of the low SMI group relative to the high SMI group. The results were reported as hazard ratios (HRs) with 95% confience intervals (CIs). The clinically relevant variables were included to adjust the potential confounders in the multivariable Cox proportional hazard models. The adjusters for adverse events and acute illness requiring transfer to other hospitals for specialized treatments were age, men, hand-grip strength, chronic heart failure, hemoglobin, creatinine, and serum albumin. To estimate the adjusted HRs for each subgroup and the interaction P values, we constructed the same multivariable Cox proportional hazard models for adverse events in the subgroups. The subgroups included age (≥75 or <75 years), men, BMI (≤18.5 kg/m2 or >18.5 kg/m2), hand-grip strength (low hand-grip strength: <28 kg in men and <18 kg in women), the HDS-R (<20 or ≥20), neurologic disease without HBD, neurologic disease with HBD, musculoskeletal disorders, hospital-associated deconditioning, chronic heart failure, chronic respiratory disease, anemia (hemoglobin ≤13 g/dL in men and ≤12 g/dL in women), baseline serum albumin (≤3.5 g/dL or >3.5 g/dL), and tube feeding at admission. In Japan, the boundary between the young-old and old-old is 75 years of age; therefore, we divided the patients into 2 subgroups: those ≥75 years of age and those <75 years of age.12 We also investigated the details of adverse events.
In the analysis of secondary outcomes, a linear regression model was constructed to examine the association of SMI with the FIM-M efficiency score or FIM-C efficiency score. The clinically relevant variables were included to adjust the potential confounders in the linear regression models. Covariates for the FIM-M efficiency score were age, men, handgrip strength, the HDS-R, hospital-associated deconditioning, neurologic disease witout HBD, neurologic disease with HBD, musculoskeletal disorders, chronic heart failure, chronic respiratory disease, tube feeding, and urinary catheter use. For the FIM-C efficiency score, covariates were age, men, the HDS-R, hospital-associated deconditioning, neurologic disease witout HBD, neurologic disease with HBD, and musculoskeletal disorders. Multicollinearity was assessed using the variance inflation factor, with a value of 1-10 indicating no multicollinearity.
Statistical analyses were performed using JMP 16 software (SAS Institute Inc, Cary, NC, USA). All P values were 2-tailed and P<.05 was considered statistically significant.
Ethics
This study was approval by the Research Ethics Committee of the Toyonaka Heisei Hospital (No. 202301) and was conducted in compliance with the Declaration of Helsinki and the Ethical Guidelines for Medical and Health Research involving Human Subjects in Japan.13 Because the data for the current study were obtained from hospital charts, written informed consent from each patient was replaced by an opt-out method. This study complies with the STROBE guidelines and reports the needed information as appropriate.
Results
Patient characteristics
Among the 409 patients who met the inclusion criteria, 299 patients (73%) were categorized as having a low SMI, whereas 110 patients (27%) were categorized as having a high SMI (fig 1). The mean ± SD age was 79 (11) (range 27-100) years and 167 patients (41%) were men (table 1).
Table 1.
Patients’ characteristics at admission
| Variable | All Patients (n=409) | Low SMI Group (n=299) | High SMI Group (n=110) | P Value |
|---|---|---|---|---|
| Age, years, mean ± SD | 79 (11) | 81 (9) | 75 (13) | <.0001* |
| Men, n (%) | 167 (41) | 123 (41) | 44 (40) | .8 |
| Body mass index, kg/m2, mean ± SD | 20.5 (4) | 19.2 (3) | 23.8 (4.6) | <.0001* |
| Hand-grip strength, kg, median (IQR)† | ||||
| Men | 18 (11-22) | 15 (10-20) | 23 (18-30) | <.0001* |
| Women | 10 (6-15) | 10 (6-12) | 13 (7-18) | .008* |
| The revised Hasegawa's Dementia Scale, median (IQR) | 15 (7-24) | 14 (6-22) | 22 (10-28) | <.0001* |
| The disease category, n (%) | ||||
| Neurological disease without higher brain dysfunction | 26 (6) | 13 (4) | 13 (11) | .004* |
| Neurological disease with higher brain dysfunction | 143 (35) | 104 (35) | 39 (35) | |
| Musculoskeletal disorders | 119 (29) | 82 (27) | 37 (33) | |
| Hospital-associated deconditioning | 121 (30) | 100 (33) | 21 (19) | |
| Comorbidities, n (%) | ||||
| Chronic heart failure | 146 (36) | 120 (40) | 26 (24) | .002* |
| Chronic respiratory disease | 24 (6) | 23 (8) | 1 (1) | .01* |
| Baseline laboratory data | ||||
| Hemoglobin, g/dL, mean ± SD | 11.5 (1.7) | 11.3 (1.7) | 12.1 (1.8) | <.0001* |
| Creatinine, mg/dL, median (IQR) | 0.7 (0.6-0.9) | 0.7 (0.6-1) | 0.7 (0.6-0.9) | .8 |
| Blood urea nitrogen, mg/dL, median (IQR) | 16.8 (12.7-22.5) | 17.6 (13.3-23.5) | 14.5 (11.7-19) | .0002* |
| Total protein, g/dL, mean ± SD | 6.5 (0.6) | 6.5 (0.6) | 6.6 (0.7) | .1 |
| Albumin, g/dL, mean ± SD | 3.7 (0.5) | 3.6 (0.4) | 3.9 (0.5) | <.0001* |
| Tube feeding, n (%) | 81 (20) | 70 (23) | 11 (10) | .003* |
| Urinary catheter use, n (%) | 41 (10) | 31 (11) | 10 (9) | .7 |
| Mobility aid, n (%) | ||||
| Wheelchair | 377 (92) | 284 (95) | 93 (85) | .0005* |
| Walker | 11 (3) | 8 (3) | 3 (3) | |
| Cane | 6 (1) | 2 (1) | 4 (4) | |
| None‡ | 15 (4) | 5 (2) | 10 (9) | |
| FIM, median (IQR) | ||||
| Motor items | 27 (15-45) | 23 (14-38) | 43 (20-59) | <.0001* |
| Cognitive items | 18 (11-27) | 16 (10-24) | 24 (15-31) | <.0001* |
Abbreviations: FIM, functional independent measure; IQR, interquartile range; SD, standard deviation; SMI, skeleatl muscle mass index.
P<.05.
Variables with missing data: hand-grip strength (35 in low-SMI group and 7 in high-SMI group).
Walking independently.
Patients in the low SMI group were significantly older than those in the high SMI group [mean ± SD age, 81 (9) years vs 75 (13) years, P<.0001]. The low SMI group had a significantly lower mean ± SD BMI than the high SMI group [19.2 (3) kg/m2 vs 23.8 (4.6) kg/m2, P<.0001] and significantly lower median (IQR) handgrip strength than the high SMI group in men [15 (10-20) kg vs 23 (18-30) kg, P<.0001] and women [10 (6-12) kg vs 13 (7-18) kg, P=.008, respectively]. Patients in the low SMI group had a significantly lower median (IQR) HDS-R than those in the high SMI group [14 (6-22) vs 22 (10-28), P<.0001] Significant differences were observed between the 2 groups in the disease category (P=.004): chronic heart failure (low SMI group vs high SMI group, 40% vs 24%, P=.002), and chronic respiratory disease (8% vs 1%, P=.01). The low SMI group had a lower mean ± SD serum albumin level than the high SMI group [3.6 (0.4) g/dL vs 3.9 (0.5) g/dL, P<.0001]. Significantly more patients in the low SMI group received tube feeding at admission than in the high SMI group (23% vs 10%, P=.003). Significantly more patients in the low SMI group used mobility aids at admission (P=.0005). Patients in the low SMI group had significantly lower median (IQR) FIM-motor scores [23 (14-38) vs 43 (20-59), P<.0001] and FIM-cognitive scores [16 (10-24) vs 24 (15-31), P<.0001] than those in the high SMI group at admission (table 1).
Outcomes
In the analysis of primary outcomes, the cumulative incidences of adverse events at 150 days were 24% in the low SMI group and 11.9% in the high SMI group (fig 2). The incidences of adverse events, that is, death and acute illness requiring transfer to other hospitals for specialized treatments, with cases per 1000 patient-days in the low SMI group and high SMI group were 2.1 vs 1, 0.3 vs 0, and 1.8 vs 1, respectively. The adjusted HRs (95% CIs) of the low SMI group relative to the high SMI group for adverse events and acute illness requiring transfer to other hospitals for specialized treatments were 2.79 (1.06-7.34) and 2.67 (1.001-7.11), respectively (table 2). In the subgroup analyses, the low SMI group had consistently higher HRs in most subgroups for adverse events. The interaction P values were not significant for any of the subgroups (supplemental fig S1). The most common adverse events were aspiration pneumonia (7 cases) and gastrointestinal bleeding (7 cases), followed by congestive heart failure (6 cases) and cerebral hemorrhage (5 cases), all of which occurred only in the low SMI group (supplemental table S1).
Fig 2.
Cumulative incidence of adverse events including death and acute illness requiring transfer to other hospitals for specialized treatments.
Abbreviations: SMI, skeleatl muscle mass index.
Table 2.
Comparison of adverse events between the 2 groups
| Outcomes | No. (/1000PD) |
Crude HRs | 95% CIs | Adjusted HRs | 95% CIs | |
|---|---|---|---|---|---|---|
| Low SMI Group (n=299) | High SMI Group (n=110) | |||||
| Adverse events, n (%) | 50 (2.1) | 8 (1) | 2.23 | 1.06-4.71 | 2.79 | 1.06-7.34 |
| Death | 8 (0.3) | 0 (0) | NA | NA | NA | NA |
| Acute illness requiring transfer to other hospitals for specialized treatments | 42 (1.8) | 8 (1) | 1.88 | 0.88-4.0 | 2.67 | 1.001-7.11 |
NOTE. Adjusters for adverse events and acute illness requiring transfer to other hospitals for specialized treatments: age, men, hand-grip strength, chronic heart failure, hemoglobin, creatinine, and serum albumin.
Abbreviations: CIs, confidence intervals; HRs, hazard ratios; NA, not assessed; PD, patient-days; SMI, skeleatl muscle mass index.
In the analysis of secondary outcomes, among the 351 patients who completed the rehabilitation program without adverse events, there were no significant differences between the 2 groups in length of stay, change in the FIM-M score, change in the FIM-C score, FIM-M efficiency score, and FIM-C efficiency score [median (IQR) length of stay, low SMI group vs high SMI group, 78 (51-93) days vs 64 (43-87) days, P=.06; mean ± SD change in FIM-M, 22 (18) vs 22,(14) P=.9; mean ± SD change in FIM-C, 3 (4) vs 3,(4) P=.9; mean ± SD FIM-M efficiency score, 0.4 (0.58) vs 0.47 (0.54), P=.3; mean ± SD FIM-C efficiency score, 0.05 (0.14) vs 0.06 (0.2), P=.4; table 3]. No multicollinearity was found between the variables in each linear regression model. The multiple linear regression models showed that the FIM-M efficiency score and FIM-C efficiency score were not associated with low SMI (β=0.064, P=.3; β=−0.05, P=.4, respectively; tables 4, 5).
Table 3.
Comparison of rehabilitation outcomes between the 2 groups completed the rehabilitation program
| Variable | All Patients (n=351) | Low SMI Group (n=249) | High SMI Group (n=102) | P Value |
|---|---|---|---|---|
| Length of stay, days, median (IQR) | 74 (47-90) | 78 (51-93) | 64 (43-87) | .06 |
| Change in FIM-M, mean ± SD | 22 (17) | 22 (18) | 22 (14) | .9 |
| Change in FIM-C, mean ± SD | 3 (4) | 3 (4) | 3 (4) | .9 |
| FIM-M efficiency score, mean ± SD | 0.42 (0.57) | 0.4 (0.58) | 0.47 (0.54) | .3 |
| FIM-C efficiency score, mean ± SD | 0.05 (0.16) | 0.05 (0.14) | 0.06 (0.2) | .4 |
Abbreviations: FIM-C, functional independent measure for cognitive function; FIM-M, functional independent measure for motor function; IQR, interquartile range; SMI, skeleatl muscle mass index.
Table 4.
Linear regression model for the functional independence measure for motor function efficiency score
| Univariate |
Multivariate |
||||
|---|---|---|---|---|---|
| β | P Value | β | P Value | VIF | |
| Low SMI group | −0.054 | .3 | 0.064 | .3 | 1.2 |
| Age | −0.066 | .2 | −0.011 | .9 | 1.4 |
| Men | 0.04 | .4 | −0.068 | .4 | 1.5 |
| Handgrip strength | 0.28 | <.0001* | 0.266 | .0005* | 2 |
| The revised Hasegawa's Dementia Scale | 0.29 | <.0001* | 0.078 | .2 | 1.5 |
| Hospital-associated deconditioning (Reference) | – | – | – | – | – |
| Neurological disease without higher brain dysfunction | 0.082 | .2 | −0.054 | .4 | 1.3 |
| Neurological disease with higher brain dysfunction | −0.043 | .5 | 0.017 | .8 | 1.6 |
| Musculoskeletal disorders | 0.122 | .056 | −0.036 | .6 | 1.6 |
| Chronic heart failure | −0.052 | .3 | −0.002 | .98 | 1.1 |
| Chronic respiratory disease | 0.007 | .9 | −0.019 | .7 | 1.1 |
| Tube feeding | −0.202 | .0001* | −0.054 | .4 | 1.3 |
| Urinary catheter use | −0.084 | .1 | −0.063 | .3 | 1.2 |
NOTE. Covariates for functional independence measure for motor function efficiency score: age, men, handgrip strength, the revised Hasegawa's Dementia Scale, hospital-associated deconditioning, neurologic disease without higher brain dysfunction, neurologic disease with higher brain dysfunction, musculoskeletal disorders, chronic heart failure, chronic respiratory disease, tube feeding, and urinary catheter use.
Abbreviations: SMI, skeleatl muscle mass index; VIF, variance inflation factor.
P<.05.
Table 5.
Linear regression model for the functional independence measure for cognitive function efficiency score
| Univariate |
Multivariate |
||||
|---|---|---|---|---|---|
| β | P Value | β | P value | VIF | |
| Low SMI group | −0.041 | .4 | −0.05 | .4 | 1.1 |
| Age | 0.0001 | .999 | 0.067 | .2 | 1.2 |
| Men | 0.056 | .3 | 0.057 | .3 | 1.1 |
| The revised Hasegawa's Dementia Scale | 0.04 | .5 | 0.065 | .3 | 1.2 |
| Hospital-associated deconditioning (Reference) | – | – | – | – | – |
| Neurological disease without higher brain dysfunction | −0.002 | .97 | 0.008 | .9 | 1.2 |
| Neurological disease with higher brain dysfunction | 0.055 | .4 | −0.08 | .2 | 1.6 |
| Musculoskeletal disorders | −0.048 | .5 | 0.028 | .7 | 1.5 |
NOTE. Covariates for functional independence measure for cognitive function efficiency score: age, men, the revised Hasegawa's Dementia Scale, hospital-associated deconditioning, neurologic disease without higher brain dysfunction, neurologic disease with higher brain dysfunction, and musculoskeletal disorders.
Abbreviations: SMI, skeleatl muscle mass index; VIF, variance inflation factor.
Discussion
This study revealed that low SMI was common in patients admitted to a rehabilitation ward and was significantly associated with adverse events such as death and acute illness requiring transfer to other hospitals for specialized treatments but not with rehabilitation outcomes including length of stay, change in the FIM-M score, change in the FIM-C score, FIM-M efficiency score, and FIM-C efficiency score.
Our findings were in line with those of previous studies reporting that sarcopenia frequently coexists with aspiration pneumonia, gastrointestinal bleeding, and cardio-cerebrovascular disease.1, 2, 3, 4, 5 The pathogenesis related to sarcopenia and its comorbidities is not yet fully understood, but the possible involvement of decreased swallowing muscle strength, hormonal imbalances such as insulin resistance, growth hormone resistance, and decreased sex hormones, oxidative stress, inflammation, apoptosis, low muscle blood flow, and endothelial dysfunction has been reported.2,3 Our findings suggested that evaluation of SMI using bioelectrical impedance analysis was a useful screening tool for predicting adverse events in patients admitted to a rehabilitation ward.
Our findings were consistent with the results of several studies showing no significant association between SMI and improvement of ADLs in the motor domain.6,7 Muscle strength and physical performance have been reported to be influenced by muscle quality as evaluated by intramuscular adipose tissue and muscle fibrosis, but not by muscle quantity as evaluated by SMI.10,14,15 Intramuscular adipose tissue and muscle fibrosis can be assessed by ultrasonography, computed tomography, and magnetic resonance imaging.10,16, 17, 18 Patients with low SMI may not have had poorer muscle quality than those with high SMI; however, these data were not assessed. In contrast, several studies have reported that low SMI was associated with poorer functional outcomes in older patients.19,20 Although many of these studies have reported on sarcopenia, the underlying mechanisms and pathophysiology of sarcopenia are not fully understood.20
Our findings also showed no association of SMI with improvement of ADLs in the cognitive domain. Our findings were consistent with those of several reports, which have not identified the reason for the lack of association between muscle mass loss and cognitive decline.21, 22, 23, 24 In contrast, several studies have reported a correlation between skeletal muscle mass and cognitive function.8,25 While the relation between skeletal muscle mass and cognitive function has not been fully elucidated, age-related systemic, chronic, low-grade inflammation, insulin metabolism, protein metabolism, and mitochondrial function have been implicated.8,25
In this study, there was no significant difference between the low and high SMI groups with respect to length of stay in the rehabilitation ward. Although there have been reports of significant associations between length of stay and change in SMI in patients admitted to rehabilitation wards, there have been no reports of associations between length of stay and baseline SMI.26,27 Time constraints (maximum hospital stay limit of 180 days) may have been a reason for the lack of a significant difference in length of stay in this study.
Limitations
There were several limitations in this study. First, the definition of adverse events was death or acute illness requiring transfer to other hospitals for specialized treatments. Because the classification of acute illness was determined by the physician in charge, the classification might not be robust. Second, changes in SMI during the hospitalization were not examined in this study. Skeletal muscle mass can be altered by intensive rehabilitation and may influence improvement in ADLs.7,28 Third, this study did not examine the details of rehabilitation protocols that might affect rehabilitation outcomes.6 Finally, because this study was conducted at a single rehabilitation hospital, the findings of this study should be applied with caution to patients admitted to other rehabilitation wards. Further studies at multiple centers are warranted to determine the effect of SMI on rehabilitation progress.
Conclusions
This study revealed that approximately 70% of patients admitted to a rehabilitation ward had low SMI. Because low SMI was significantly associated with adverse events, patients with low SMI should be strictly managed during their hospitalization. Further research is needed to determine whether SMI is more useful as a predictor of adverse outcomes than physical performance such as gait speed and grip strength, which have also been reported as predictors of adverse outcomes.29 There was no significant association between baseline SMI and rehabilitation outcomes among patients who completed the rehabilitation program. Not only muscle quantity but also muscle quality must be examined to evaluate the association between muscle and rehabilitation outcomes. Until the truth is determined, patients should be provided rehabilitation that increases both muscle quantity and quality, such as resistance training.10,14,15,30
Acknowledgments
We are grateful to all the staff in the rehabilitation ward at Toyonaka Heisei Hospital who sincerely provide rehabilitation services to improve patients’ ADLs.
Footnotes
Disclosures: The investigators have no financial or nonfinancial disclosures to make in relation to this project.
Supplementary material associated with this article can be found in the online version at doi:10.1016/j.arrct.2023.100314.
Appendix. Supplementary materials
Supplemental Fig 1 Subgroup analyses of adverse events including death and acute illness requiring transfer to other hospitals for specialized treatments. BMI, body mass index; CIs, confidence intervals; HRs, hazard ratios; NA, not assessed.
Supplemental Table 1 Details of adverse events among patients who were admitted to the rehabilitation ward
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Associated Data
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Supplementary Materials
Supplemental Fig 1 Subgroup analyses of adverse events including death and acute illness requiring transfer to other hospitals for specialized treatments. BMI, body mass index; CIs, confidence intervals; HRs, hazard ratios; NA, not assessed.
Supplemental Table 1 Details of adverse events among patients who were admitted to the rehabilitation ward