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Winning Abstracts from the 2007 Medical Student Abstract Competition: Distribution of Total Body Water in Acutely Ill Elderly Patients

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Author:
Nitin K. Gupta, Vanderbilt University School of Medicine, 2007

Introduction:
Multifrequency Bioelectrical Impedance Analysis (MBIA) is used in clinical settings to estimate body composition and interstitial and extracellular water compartments. The objective of this study is to validate MBIA as a clinically useful tool for the measurement of total body weight (TBW) and lean body mass in critically ill patients. In healthy individuals, changes in body weight can estimate changes in TBW. In critically ill patients, however, TBW does not reliably reflect fat free mass due to intracellular disturbances caused by protein malnutrition, changes in total body water and in the ratio of intracellular and extracellular water (ECW) due to injury and inflammation. These values are of clinical significance because in acutely ill patients, the amount of lean muscle mass is often overestimated by anthropometric equations when compared to actual values measured by the segmental compartments of TBW or intracellular water (ICW). Therefore, an undetected decrease or increase in ICW could cause errors in estimation of drug doses calculated based on body mass. Additionally, measurement of ECW is of considerable clinical importance since excessive fluid retention in the extracellular space is known to cause increased morbidity in critically ill patients. Currently, the only approved method for determining TBW in this patient population is via isotope dilutions, which are impractical tools for use at bedside due time limitations and cost. This study attempts to validate MBIA as a clinically useful tool in measuring TBW and ECW in critically ill patients by correlating results obtained using MBIA to reference measurements for TBW using deuterium dilution and ECW using sodium bromide.

Methods:
TBW and ECW will be measured utilizing a multifrequency bioimpedance SEAC SFB3 analyzer. Thirteen critically ill patients were enrolled in the pilot study. Testing was conducted at bedside, in the morning, and at least two hours after the last meal. Body height and weight were recorded from the patients’ charts. Following MBIA, research participants will receive isotope dilutions to measure TBW and ECW.

Results:
When comparing TBW and ECW measurements obtained using MBIA and calculated using anthropometric equations, we found a significant difference in amount of TBW between these two methods (p=0.01). When using MBIA and isotope dilutions, however, there was no significant difference in ECW between these two methods (p>0.05). Anthropometric methods resulted in overestimation of TBW and ICW (p=0.001).

Conclusion:
We found MBIA easy to administer at bedside and well tolerated by the patients. Preliminary data on ten acutely ill elderly subjects suggests that MBIA may reliably estimate TBW and that anthropometric methods are not a reliable tool to determine TBW and ICW in acutely ill patients.

Back to May 2007 Issue of IMpact

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