Newsletter

[ Vol. 6 No. 2 ] (May - August 2005 )
Body composition measurement and its application to clinical practice

Ross C. Smith MD, FRACS.
Associate Professor in Surgery, The University of Sydney, Australia.

Good health implies normal body composition (BC). Keysû study of partial starvation demonstrated that starvation induced a significant loss of functioning tissue or Body Cell Mass (BCM) and fat stores and that the recovery of BCM took longer than the time taken to lose this tissue. Further, in this study extracellular fluid volume (ECV) was maintained. Thus starvation alone resulted in a relative increase in ECV to BCM. This effect is exaggerated in septic and traumatized ICU patients. Depletion of BCM and its associated protein results in increased morbidity and mortality.

Anthropometry and bioelectrical impedance are simple methods for bedside body composition assessment. Most assessments relate to the measurement of body fat and water and the partitioning of the lean body mass into the intra-cellular and extra-cellular compartments. Total body nitrogen (TBN) and Total body potassium (TBK) can be measured directly by nuclear techniques which require specialized equipment. These measures can be used to assess muscle mass and visceral mass because of the greater intracellular potassium concentration in muscle. DEXA can also be used to measure these compartments. The relative merits of these techniques will be discussed.

Isotope dilution studies developed by Moore and others have substantiated fluid and electrolyte requirements of ill patients and have been used in important early studies of BC in ICU patients by Shizgal et al. They demonstrated that BCM predicted outcome, resting energy expenditure, and assessed patients’ response to nutritional therapy.

Professor Hill’s sophisticated BC laboratory was close to the ICU. His team could measure TBN, TBK, TBCl, TBW, etc and they described the difficulties of maintaining these values in patients in the ICU setting. Although they have shown that it was easy to provide sufficient calories to maintain fat stores, it was difficult to provide sufficient amino acids to maintain protein stores in severely traumatized patients.

Our studies after major surgical trauma have indicated that there is improved muscle sparing if greater amounts of nutrition are provided. Further, measures demonstrating depleted body composition can predict poor outcome in many different patient groups including ICU, surgical, renal failure patients and in many other groups. Body composition measures have limited value in the management of individual patients in the ICU setting, although they have a proven place in individual patient care in the event of renal failure. However, by studying groups of patients undergoing specific protocols these measures are important outcome measures demonstrating benefit. They become most important when clinical outcome endpoints are unable to be used because group sizes lack statistical power.
 

From 
“The Future of Nutrition Support and Cooperation Among the Asian Regions”
The 10^th PENSA Congress, Dusit Resort Pattaya, Chonburi, Thailand. 
October 27-29, 2004: Page 70