Hip fracture prognosis: could bioimpedance be an alternative to conventional nutritional assessment?

Pronóstico de la fractura de cadera: ¿podría la bioimpedancia ser una alternativa para la evaluación nutricional convencional?

L. Schiper¹, D. Sadigursky¹, D. A. V. Rosario¹, S. P. Schiper¹, L. C. Passos² and J. Faintuch³

¹Orthopedic and Traumatologic Clinic. Salvador. BA. Brazil.
²Department of Cardiology. School of Medicine. Federal University of Bahia. Salvador. BA. Brazil.
³Department of Gastroenterology. Hospital das Clinicas and Sao Paulo University Medical School. Sao Paulo. SP. Brazil.

ABSTRACT

Background: Risk-factors for mortality in hip fractures encompass nutritional status, nominally body mass index, but not body composition. Given the difficulty of anthropometric assessment in bedridden patients a prospective study with bioimpedance analysis was designed.
Methods: Elderly patients with hip fracture were consecutively recruited. Biochemical tests, primitive bioimpedance measurements (resistance, reactance and phase angle) and follow-up till one year were targeted.
Results: Patients (N = 69, 81.2 ± 8.1 years old, 72.5% females) stayed in the hospital for 15.5 ± 17.1 days, and 18.8% (13/69) required further hospitalization during the ensuing months. Mortality was 11.6% within 30 days, coinciding with hospital mortality, and an additional 11.6% till one year, thus reaching 23.2%. Anemia, hypoalbuminemia and low transferrin, along with elevated glucose and urea were frequent, suggesting undernutrition with metabolic derangements. Reactance, urea and creatinine were different in patients suffering both early and late demise. Resistance, white blood cell count and osteoporosis were risk factors for early mortality only , and anemia exclusively for late mortality.
Conclusions: Primitive bioimpedance measurements, which had not been hitherto investigated , were prognostically related to early and late mortality. These markers of disease-related malnutrition and especially reactance should be further studied in patients unfit for anthropometric evaluation due to fracture and immobility.

Key words: Hip fracture. Malnutrition. Bioimpedance analysis. Reactance. Body mass index. Morbidity. Mortality.

RESUMEN

Palabras clave: Fractura de cadera. Desnutrición. Análisis de bioimpedancia. Reactancia. Índice de masa corporal. Morbilidad. Mortalidad.

Introduction

Several demographic, clinical, and nutritional findings are prognostically important for mortality after hip fracture in the elderly.^1-3 Besides osteoporosis which is believed to be the hegemonic predisposing factor, emphasis is often given to low body mass index,³ however this is not an easy measurement in recumbent persons with major bone trauma. Not more than half of the hospitals adopt any modality of nutritional screening,⁴ therefore BMI values from previous admissions are hardly an option. Reported or estimated heights are not reliable either⁵ and traumatic edema may be a pitfall for weight interpretation, thus rendering BMI utilization questionable.

Bioimpedance analysis (BIA), though an accepted measurement of nutritional status and body compartments, has not been investigated in this context. In a prospective protocol, the hypothesis was that both early and late mortality could be associated with changes in BIA indices, especially with reactance which is sensitive to body fluid shifts.^6-9

Sixty-nine consecutive patients were investigated, 34 with fracture of neck of femur and 35 with intertrochanteric lesion. Groups were demographically and metabolically well matched therefore they are analyzed together.

Inclusion criteria were age > 65 years (males and females) and informed consent. Exclusion criteria were sepsis, shock, coma, pathologic fracture, use of corticosteroids, previous operation of the hip, use of pacemaker or refusal to participate in the protocol. Informed consent was given by all patients or caregivers, and the protocol was approved by the Institutional Ethical Committee.

Questionnaires targeting demographics and comorbidities were used, and diagnosis was based on current treatment. Derived BIA compartments (lean body mass, body fat and total body water) were not part of the protocol, only primitive findings (resistance, reactance and phase angle),as weight and height would be required in the equation. Fracture risk assessment according to the WHO/FRAX algorithm was not computed either, due to lacking BMI.¹ The standard tetrapolar technique was applied at the healthy side of the body, after overnight fasting and voiding (BIA Quantum II, RJL Systems, Clinton Township, MI, USA). Serum albumin, transferrin, BUN, creatinine, along with hematologic counts were measured by automated methods. Principal end-points were 30-day and one year mortality. Results (mean ± SD or percentage) were compared by Chi-Square test, analysis of variance (ANOVA) or Student's "t" test as appropriate. Classification by tertiles for comparison of risk factors was also conducted.

Results

Patients were mostly females, and arterial hypertension, osteoporosis along with diabetes were fairly prevalent. Nearly one fifth required additional admission during the ensuing 12 months, mostly because of falls and clinical problems.

Participants suffered from some degree of anemia, hypoalbuminemia and low transferrin. In contrast white blood cell count (WBC) tended to be elevated, consistent with acute trauma and inflammation. Nevertheless creatinine was normal, with no case above 2 mg/dL (table I).

One year mortality was linked to reactance (P < 0.001) and anemia (P = 0.039). Noteworthy findings concerned also BUN and creatinine, both of which interfered with early and total mortality (P < 0.001).

Figure 1 illustrates impact on one-year mortality according to reactance values, and for comparison those of creatinine as well.

Discussion

Proximal femoral fracture is the most severe lowenergy trauma and the paramount complication of osteoporosis, as it tends to followed by morbidity, disability and particularly mortality.^1,2,10

Recent studies unveil excess mortality not only during 12 months, but up to 10 years.^2,10 One is not dealing with an ordinary traumatic disorder, but with a cluster of abnormalities encompassing osteoporosis, frailty, impaired nutrition and organ dysfunctions.

In the WHO/Canadian series based on more than 46,000 subjects, osteoporosis was deemed relevant but not overarching, as mechanical fragility is only part of the context. Clinical risk factors were indispensable to develop a fracture risk assessment tool including prior fractures and family history, age, gender, body mass index, ethnicity, smoking, alcoholism, glucocorticoid use and rheumatoid arthritis.¹

The importance of protein-energy compartments in these studies is underscored in a meta-analysis targeting BMI, with a total follow-up of over 250,000 person years.³ Indeed, deranged nutritional status could underlie several of the alluded to comorbidities including alcoholism, rheumatoid arthritis and perhaps osteoporosis itself, notably in subjects with substantial weight loss.¹¹

Primitive bioimpedance measurements, nominally resistance and reactance, are weight-independent and thus ideal for bedridden patients. To the best of our knowledge, this is the first study to demonstrate that resistance and reactance could be employed for early as well as late mortality investigation.

Decreased resistance points toward underweight whereas low reactance signals body fluid shifts (overhydration),^6-9 conditions consistent with anemia, systemic inflammation and possible renal compromise as here demonstrated. Bioimpedance analysis could thus represent an advantage in comparison to classic anthropometrics (BMI, body weight changes), which do not distinguish between water retention or elimination and changes in fat and lean body mass.

In synthesis these variables, particularly reactance, are more specific for disease-related malnutrition,⁹ and severely impaired mobility is not a deterrent to their adoption.

Acknowledgments

This study received no financial grant and the authors have no conflict of interest to declare.

References

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Correspondence:
Joel Faintuch.
Hospital das Clinicas.
Av. Eneias C. Aguiar, 255.
CP: 05043 São Paulo. Brazil. ]]> E-mail: jfaintuch@hcnet.usp.br

Recibido: 7-III-2011.
Aceptado: 5-IV-2011.