Can Bioelectrical Impedance Analysis Identify Malnutrition in Preoperative Nutrition Assessment?

Abstract

Objective:

Malnutrition is characterized by changes in cellular membrane integrity and alterations in fluid balance, both of which can be detected by bioelectrical impedance analysis (BIA). We investigated whether BIA-measured variables could detect malnutrition, as defined by the Subjective Global Assessment (SGA), in preoperative surgical patients.

Methods:

We prospectively evaluated 279 patients hospitalized for elective gastrointestinal surgery during the first 72 h after admission. BIA estimates were used to derive body cell mass, ratio of extracellular mass to body cell mass, and phase angle. Malnutrition diagnosed with these measures was compared with the SGA score. Receiver operating characteristic curves also were formulated to explore alternative cutoff points for one measure, phase angle.

Results:

A linear trend for means across SGA categories was found for all indicators used, except percentage of body cell mass. However, there was only fair overall agreement between SGA and BIA estimates. The receiver operating characteristic curves for phase angle suggested that the test was too sensitive or too specific. No alternative cutoff points resulted in suitable tests that could provide an alternative to SGA.

Conclusions:

Although not in close agreement with SGA, the results suggested that there are some alterations in tissue electrical properties with malnutrition that can be detected by BIA. New cutoff points may be needed for application of BIA as a complementary method in the nutrition assessment of surgical patients.

Introduction

The prevalence of malnutrition in hospitalized patients has been the subject of many papers in the past 20 y. Studies from many centers have reported prevalences of 30% to 50% in clinical and surgical patients.1, 2, 3 Malnutrition in hospitalized patients has been associated with a higher incidence of complications and mortality. Complications associated with malnutrition in surgical patients seem to be related to functional status rather than to body composition alterations.⁴ Thus, an optimal nutrition assessment test should be capable of detecting organic functional impairment resulting from malnutrition. In this sense, malnutrition would become a general marker of changes in health status that are caused by different factors and not only by an inappropriate nutrient intake.⁵

Among the several methods used for nutrition assessment in hospitalized patients, the Subjective Global Assessment (SGA) stands out as simple, safe, and inexpensive. SGA classes are associated with other objective measurements (convergent validity).⁶ In the absence of true reference tests that incorporate body composition and physiologic function to diagnose malnutrition in hospitals, the evaluation of new proposed tests has been made because of their ability to identify patients who might suffer from “complications associated with malnutrition” during hospitalization. The SGA has been shown suitable to identify surgical⁷ and oncologic⁸ patients with a higher risk of nutritional complications and who might benefit from nutrition therapy. Nevertheless, it would be useful to have objective tests that could not only identify patients at risk but also quantify the risk and monitor nutrition therapy.⁹

Bioelectrical impedance analysis (BIA) is a simple, quick, non-invasive method that is used to assess body composition at the bedside.¹⁰ Body composition evaluation using BIA is based on regression equations that use resistance (R) and reactance (Xc) parameters to estimate total body water, lean body mass or fat-free mass, body cell mass (BCM), and body fat. Criticism of this kind of analysis has been based on two of its suppositions: that tissue hydration is constant in all individuals (healthy, obese, critical and surgical patients, etc.) and that the human body behaves as a cylinder that homogeneously conducts the electrical flow.¹¹ Thus BIA is not a good method for the evaluation of body composition in situations where tissue hydration is altered.¹⁰ However, the method was considered satisfactory as a BCM predictor when compared with the whole-body potassium method.¹² BCM, as independent from extracellular water variations, would not present any use limitations in different clinical conditions.¹³ Thus, evaluation of BCM through BIA could be indicative of body composition variations. Phase angle (PA), obtained directly from R and Xc values, is the difference between voltage and current and can be used as an indicator of BCM. Thus, changes in BCM and functional defects of the cellular membrane can result in changes in impedance and PA.¹⁴ Clinical studies associated low BCM15, 16 or low PA¹¹ with morbidity and mortality in patients on hemodialysis or with human immunodeficiency virus (HIV). BCM and PA can be considered nutrition indicators,¹⁷ and for this reason their assessment may be useful in preoperative assessment of surgical patients.

Our objective was to compare the performance of BIA, an objective method of nutrition assessment in surgical patients, with SGA, considered here as the reference method. BIA was evaluated not only as a body composition assessment method but also through its direct biophysical components R, X_c and PA.