Lean body mass calculation

Forbes, G. B. Hursh, J. B. (1963) Age and sex trends in lean body mass calculated from K-40 measurements with a note on the theoretical basis for the procedure. Ann. N.Y. Acad. Sci. 110, 255-263. 

Poorly perfused tissues (adipose tissue, connective tissue, and bone) require hours to come into equilibrium with plasma drug concentrations (Fig. 25.1). Since the accumulation of anesthetic in body fat is relatively small soon after its IV administration, it is common clinical practice to calculate drug dosage on the basis of lean body mass rather than on total body weight. Thus, an obese patient may receive the same dose of IV anesthetic as a patient of normal body weight. 

Of 30 patients who were treated with colistin for more than 48 hours and were retrospectively reviewed, 10 developed nephrotoxicity [105 ]. Patients who were given excessive doses based on their actual body weight (as opposed to ideal body weight) were 13 times more likely to develop nephrotoxicity. Concomitant use of diuretics and/or vasopressors was also associated with nephrotoxicity. The authors concluded that it may be better to use a measure of lean body mass to calculate doses of cohstin. 

The density of body fat is 0.9 g/mL, whereas that of the fat-free body mass is 1.10 g/ mL. This means that, if the density of the body can be calculated, then the proportion of fat and lean tissue can be calculated. 

Once the protein and lipid mass are known, the liveweight of the animal can be calculated from its body composition as the smn of its water, ash, protein and hpid content, assuming that lean tissue contains approximately 238 g/kg protein and that gut fill constitutes 60 g/kg liveweight, as follows ... 

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