The prevalence of obesity in America is increasing at an alarming rate. Recent data have suggested that 69.2% of American adults, aged 20 years and older, are overweight.1 Furthermore, 35% of this same population are obese. This rising trend in obesity parallels an impact on related morbidity and mortality.2 For example, a higher percentage of patients presenting with coronary heart disease, hypertension, diabetes, and stroke are in fact obese as well.3 The implication of obesity as a stroke risk factor has well been established. Specifically, obesity contributes to the development of cardiac and atherosclerotic complications leading to stroke. Although obesity continues to be associated with adverse health consequences, there are emerging data leading to a reassessment of obesity and its impact on morbidity and mortality, especially among those undergoing hospitalization.
One wave of investigation regarding the effect of body mass index (BMI) on recovery comes from an unlikely source in cardiology where the coined phrase “obesity paradox” emerged. This phrase suggests that overweight patients are more likely to contract a heart disease compared with those with a healthier BMI, but are also found to have a better prognosis after such an event than those with a leaner BMI.4–7 Many studies have openly suggested that obesity may offer a clinical advantage as it relates to post-cardiac outcomes including morbidity, length of stay, and mortality.
There are limited data concerning the effect of BMI on outcomes in a rehabilitation setting. In a study of patients admitted for rehabilitation with debility, Jain et al.8 found that obese patients realized more gains in functional independence measurement (FIM) scores than normal-weight patients. Similarly, among patients recovering from total hip arthroplasty (THA), Vincent et al.9,10 found that BMI does not hinder patients from achieving FIM gains while they are recovering in an inpatient rehabilitation facility. However, in the few studies of patients admitted for rehabilitation after lower-limb amputation, authors have found no correlation between BMI and functional outcome.11,12 The current study was therefore designed to further investigate the correlation between BMI and functional gains among a cohort of patients admitted for acute rehabilitation after a lower-limb amputation.
Data were analyzed during the period of January 2000 to April 2006 from all previously amputated patients admitted and discharged from an acute freestanding rehabilitation hospital. Data were retrieved from the medical record including diagnosis, height, and weight measured before amputation, FIMs scored on admission and discharge, and the length of rehabilitation hospitalization. During the study period, 327 patients met the requirement of rehabilitation related to amputation. All subjects were admitted directly from the acute care hospital at which the amputation was performed. The level of amputation was not available in the data for analysis. The body mass index (BMI) was calculated for each patient, which is body weight (in kilograms) divided by height (in meters squared). These patients were then separated into six separate groups according to BMI. The BMI of the underweight group was less than 18.5 kg/m2, the normal group was 18.5 to 24.9 kg/m2, the overweight group was 25 to 29.9 kg/m2, the obese I group was 30 to 34.9 kg/m2, obese II was 35.0 to 39.9 kg/m2, and the obese III was 40 kg/m2 or more. FIM score efficiency was calculated by dividing FIM score change by the length of stay. The FIM gains were calculated for each individual, and then averaged for each weight category and compared, looking for statistically significant differences between the six distinct weight groups.
Baseline demographic and FIM scores were compared between the six weight categories with a one-way analysis of variance for continuous variables and a χ2 test for proportions (Tables 1–3). Multivariable regression analysis of FIM gain was performed with BMI categories as independent variables adjusting for sex, age, and length of hospital stay. All statistical tests were two-sided. A P value of 0.05 or less was considered statistically significant.
All patients admitted to the inpatient rehabilitation amputee unit between January 2000 and April of 2006 were considered for inclusion of the analysis. During this time, 327 patients were admitted to the unit with an average age of 64 years, with ages ranging from 51 to 79 years. The median age of the underweight group was 77 years, the normal-weight group was 68 years, the overweight group was 69 years, with obese groups I, II, and III being 63 years, 55 years, and 58 years, respectively.
Of the patients admitted, 62% were male, including 28% of the underweight group, 66% of the normal group, 65% of the overweight group, 65% of the obese I group, 55% of the obese II group, and 62% of the obese III group.
The median admission FIM scores were 76 in the underweight group, 71 in the normal weight group, 72 in the overweight group, 69 in the obese I, 67 in obese II, and 66 in obese III. Discharge FIM scores were also similar between weight categories with a median of 94 in the underweight group, 94 in the normal group, 94 in the overweight group, and 97 in the obese group I, 100 in obese group II, and 93 in obese group III.
Table 1 summarizes the demographic and FIM scores for the 327 patients with amputation and by weight category. These data demonstrate that 7.6% were underweight, 41.3% were normal weight, 26.3% were overweight, 12.2% were obese I, 6.1% were obese II, and 6.4% were obese III. Sex and age differences were identified between the four weight groups. The mean FIM efficiencies of the underweight, overweight, normal, and obese I, II, and III were, 0.7, 0.6, 0.5, 0.6, 1.0, and 0.6, respectively.
Both the one way analysis and the χ2 analysis demonstrate that the FIM efficiency of the patients in the obese class I category was significantly better than those in the normal weight reference group (P < 0.05 for both) (Table 2 and Table 3).
There is a significant body of literature that has reviewed the effect of BMI on the health of the individual. This has become of increasing interest as the rate of overweight and obese individuals in the United States and the rest of the world steadily climbs.13 Direct associations have been noted between obesity and several diseases, including diabetes mellitus, hypertension, dyslipidemia, and ischemic heart disease. Despite this, the relationship between body weight and all-cause mortality is more controversial. It has long been recognized that very high degree of obesity (BMI >35 kg/m2) seems to be linked to higher mortality rates,1 but the relationship between more modest degrees of overweight and mortality is less clear. In The Harvard Alumni Study14 of more than 19,000 middle-aged men, the authors noted that a U-shaped relationship existed between BMI and mortality after adjustment for age, cigarette smoking, and physical activity, with elevated mortality among the lightest and the heaviest of the subjects. This U-shaped data were also noted in other large studies,15–18 including the Nurses’ Health Study, which showed a U-shaped relationship between BMI and all-cause mortality in women.17
Others have studied the relationship between BMI and outcomes among those who are hospitalized. In the trauma literature, data suggest that overweight patients are prone to develop more complications after trauma than are lean patients. Choban et al.19 found that, after blunt trauma, patients with a BMI over 30 kg/m2 had significantly higher mortality rates than overweight or normal-weight patients. In this study, the severely overweight patients experienced more complications, mainly pulmonary in nature. In a prospective study of trauma patients, Bochicchio et al.20 found that, when controlling for other factors, obese patients were 7.1 times more likely to die in the hospital. Meroz and Gozal21 found that obese trauma patients are far more likely to develop in-hospital complications, especially pulmonary, renal, and thromboembolic complications than are their normal-weight counterparts. Neville et al.22 found obesity to be an independent risk factor of mortality in severely injured blunt trauma patients and showed that patients with a BMI of greater than or equal to 30 experienced a twofold increase in mortality compared with lean patients and a fourfold increase in the rate of multiple organ failure. Brown et al.23 reviewed the impact of obesity on the outcome of 1153 critically injured blunt trauma patients and found obesity to be an independent risk factor for mortality (odds ratio, 1.6). In their study, obese patients experienced more overall complications, multiple system organ failure, more adult respiratory distress syndrome, and more renal failure requiring dialysis. Meroz and Gozal21 also concluded that the BMI is an independent risk factor for morbidity and mortality after trauma. Others have questioned this. In a meta-analysis, Akinnusi and Pineda24 noted that obesity in critically ill patients was not associated with excess mortality but is significantly related to prolonged duration of mechanical ventilation and intensive care unit (ICU) length of stay.
In the stroke literature, obesity has been linked to an increased risk of stroke in both men and women.23–27 In a study of 234,863 Korean men aged 40 to 64 years, Song et al.28 found an adjusted hazard of 11% for ischemic stroke for each 1 point increase in BMI. In the Physicians Health Study of 21,414 US physicians, those with a BMI greater than 30 kg/m2 had a relative risk of 1.95 for an ischemic stroke and a relative risk of 2.25 for a hemorrhagic stroke. In this study, each 1 point increase in BMI resulted in a 6% increase in the relative risk for total stroke.23 In a study from Sweden of 7402 healthy men aged 47 to 55 years, followed up over a 28-year period, a BMI greater than 30 kg/m2 resulted in a hazards ratio of 1.78 for ischemic stroke, but not hemorrhagic stroke.29 The increased risk for stroke persisted in these studies, after adjusting for risk factors such as hypertension, diabetes, and hypercholesterolemia.
The reasons behind the increase in mortality and morbidity in the extremely overweight have been explored. It has been shown that hospitalized obese patients are at an increased risk of developing respiratory and other complications.19,30 It is likely that obesity increases the incidence of complications in patients admitted to the ICU and that these complications are associated with a longer hospital stay and an overall worse outcome.
There are several studies that have reviewed the effect of BMI on the outcome of those in a rehabilitation setting. In a retrospective study, Vincent et al.9 reviewed the cases of consecutive obese and nonobese patients with diagnoses of either primary THA or revision THA. This study found a curvilinear relationship between BMI and FIM efficiency, with the best efficiency realized in the overweight group and the worst in the severely obese group. In another retrospective study, this time of total knee replacement (TKR) surgeries, Vincent found that the FIM efficiency was lowest in the severely obese as compared with the remaining groups (3.7 points/day vs 4.0–4.3 points/day; P = 0.044) and that the severely obese group had higher total physical and occupational therapy and pharmacy charges than did the remaining groups (P < 0.05). In this study, the overweight and moderately obese had the greatest FIM efficiency among the primary knee replacement. Stevens-Lapsley et al.,31 looking at 140 patients with BMIs ranging from 21.2 to 40.0 kg/m2 and followed over the first 6 months after unilateral TKA, found no meaningful relationships between BMI and functional performance in the subacute (1 and 3 months) and intermediate (6 months) stages of recovery.
There are no large studies of which we are aware that explore the association between BMI and recovery during hospital rehabilitation among patients with an amputation. Therefore our study, which examined FIM scores for all amputated patients over a period of 6 years, is the first large study to provide evidence that obesity is not a risk factor for impaired functional progress of patients with amputation patients in a rehabilitation unit. Our data suggest rather that patients with amputations do best who enter the rehabilitation hospital with a BMI in the range of obese class I.
This study is limited by the retrospective nature of the analysis. Another study limitation of the study is the lack of assessment of the effect of age on the FIM efficiency. It may have been that the advanced age of the underweight group, relatively normal on overweight groups, could have been a factor contributing to a lower FIM efficiency in this group. It is not known whether the age of those admitted to the rehabilitation hospital after the amputation is representative of those undergoing amputation and discharged from the admitting hospital. In addition, it is not known whether the weights of those admitted to the rehabilitation hospital are representative of the weights of all with amputation.
This study demonstrates that among a large group of patients with an amputation, those with a BMI in the obese class I have a better functional progression than do normal-weight patients with no other significant differences found in the other weight classes.
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