Abbreviations
Background
Calculationof Fat Free Mass and Body Cell Mass
Nutrientsper Kilogram of Body Cell Mass
Pediatric Module
Questions and Comments
BMI(Wt/Ht 2)=BodyMass Index
IBW(kg)=Ideal Body Weight
BSA(m 2)=Body Surface Area
TBW(L)=Total Body Water
LBM(kg)=Lean Body Mass
BCM(kg)=Body Cell Mass
FFM=Fat Free Mass; FM=Fat Mass
REE=Resting Energy Expenditure
TEE=Total Energy Expenditure
(1 Kcal= 4.184 Kjoules)
This program attempts to obtain a consensus amongusers to prescribe nutritional support as accurately as possible.In this context, precise daily nutrient intake does notcharacterize normal human behaviour. Nor is it clearly established that energy expended should be provided overthe short term in acute trauma or illness to patients previously not malnourished. When we are sick or injured, we have evolved as a species to avoid food. The purpose of this program is to devise the "best" algorithm to prescribe satisfactory adult parenteral and enteral nutritional support.
Variations in body composition related to gender,ethnicity, age, stature, disease, and obesity influence precision in using average data for prediction of energy expenditure and nutrient requirements. Body weight is a poor reference for nutritional support because individuals, men and women of the same weight, for example, differ in body composition. Men, on average, have less fat and more lean tissue. It is the lean tissue(12), or more specifically the body cell mass (BCM), which consumes oxygen and burns fuel, such as carbohydrate and fat, for energy(8). Total body water, a major constituent of BCM, has been shown to correlate closely with oxygen consumption, as an indicator of energy expenditure(13). It seems logical, therefore,to know BCM for any given patient and to use BCM as a reference for nutritional support. Measurements of BCM or constituents from which it is derived, such as total body water and potassium, are generally cumbersome, time-consuming, and expensive. Bioimpedance analysis may be used to measure TBW and BCM (14), but in patients with fluid derangements, this technique is subject to error(15).
TBW and BCM can be calculated from simple anthropometric measurements as gender, age, height, and weight.Although precision is desirable in these calculations, there is significant variation in human stature and body composition, the components of BCM. Excess body water can be estimated by short term weight change (1 kg=1 liter). Excess energy expenditure must either be estimated or measured by indirect calorimetry(1) when this capability is available . In 140 ICU patients, receiving TPN as 25% glucose, energy expenditure was measured by indirect calorimetry and glucose intake was documented(16). Measured energy expenditure was 1.2±0.25 kcals/day x Harris-Benedict calculation. In 47% of these ICU patients having a respiratory quotient (RQ)>1.0,indicating net lipogenesis, the average glucose intake was 4.48mg/kg/min. This would be comparable to about 2 liters of 25% dextrose/day. Those patients with an RQ<1.0 had a glucose intake of 2.89 mg/kg/min, comparable to 2 litersof 15% dextrose/day. We have recently reported hazards of excessive glucose administration in TPN as used in US academic medical centers(17). The wide range of values and coefficients ofvariation of >20% imply the need for standardization of TPN.
CALCULATION OF FAT-FREE MASS(FFM) AND BODY CELL MASS (BCM)
TBW is calculated by the equations of Watson etal(18), as follows:
With height available:
TBW=11.29 - 7.262 x Sex (M=1;F=2) - 0.070408 x Age + 0.1158 x Ht+ 0.2837 x Wt
rČ=0.79
Without height available:
Male: TBW=20.03 - 0.1183 x Age + 0.3626 x Wt
rČ=0.689
Female: TBW=14.46 + 0.2549 x Wt
rČ=0.717
TBW is corrected for 5% non-aqueous hydrogen as TBW x0.95 (19).
In measurement of FFM and TBW in 668 adults(20), the average hydration of FFM was about 74% for adult men and women:
| Black males | White males | Black females | White females | |
| N | 95 | 204 | 99 | 270 |
| TBW x 100/FFM (%) | 74.4 | 74.0 | 74.9 | 73.8 |
Therefore, for men and women: FFM=TBW/0.74
Body Cell Mass(BCM) is calculated for men and for women(21) as:
Males:
BCM(kg)=2.72 + 0.48 x FFM
or: BCM(kg))=2.72 + 0.48 x (TBW/0.74)
Females:
BCM(kg)=0.93 + 0.47 x FFM
or: BCM(kg)=0.93 + 0.47 x (TBW/0.74)
As the authors point out, however(21), water content of FFM is a function not only of gender but age, ECF, and ECF solids.Substituting various values for TBW, BCM is 70% ± about 5% ofTBW. For anorectic and severely obese (BMI>40) patients,individual prescriptions will need to be prepared on the basis of measured REE or modified calculations. In obesity about 25% of weight in excess of IBW is lean tissue(22).
Resting energy expenditure(REE) is calculated either from the equation of Cunningham (23) as:
REE(kcals) = 370+21.6 x FFM
or by the equation of Nelson et al(24) as:
REE(kjoules) = (108 x FFM) + (16.8 x FM)
r2 =0.986
(1 kcal = 4.184 kjoules)
These two equations provide values for REE within about 5% of each other. The equation of Nelson et al(24) has been selected because of the high coefficient of determination reported.
These equations provide values for REE about 15% less than those calculated by the Harris-Benedict equations (25). An activity or stress factor of 20% using Harris-Benedict equations would therefore be 40% using equations of Cunningham or Nelson.
NUTRIENTS PER KILOGRAM OF BODY CELL MASS:
To determine "dry" body weight, excess body water may be estimated from short term weight change(1kg=1 liter) or by physical examination. Deep pitting ankle edema may represent 10-20 liters, or more, of excess body water, as measured by deuterium dilution(26).
After calculation of TEE, TPN is prescribed with 20% of energyas AA, 60% as carbohydrate, and 20% as fat. "Standard "TPN at the University of Kansas Medical Center is 4.25% AA, 15% Dextrose, and 20% fat emulsion (usually 200ml), given all-in-one(17).
For a 21 year old male, 70kg, height 72", with60% TBW, 29.4kg BCM, and a stress factor of 40% (20% forHarris-Benedict calculation) requiring 2.4 liters of fluid/day,TPN Nutrients provided per kg BCM are:
Amino acids: 3.4g/kg BCM/day (=1.5g/kg body weight)
CHO: 12g/kg BCM/day (=3.5mg/kg/min)
Fat: 2.3g/kg BCM/day
Kcals: 70 kcals/kg BCM/day
Water: 75ml/kg BCM/day.
From polynomial equations derived from standard pediatric weight/height charts (29) the ideal weights, heights,and weights for heights are determined. Body Cell Mass (BCM) is used as a reference for nutritional support (30).
Calorie requirement for males and females is derived from Kerner (31), with equations derived from the ranges of data cited:
Kcals/kg =99.24-10.02*A+2.065*A2-0.2269*A3+0.0107*A4-0.000188*A5
Recent publications (32,33), using stable isotope methodology, conclude that glucose should not be given at greaterthan 5mg/kg body weight/min in pediatrics, a value only slightly greater than that for adults (4mg/kg/min).
For children less than 10 yrs or <30kg, the standard TPN solution is 3% amino acids, dextrose in an amount and concentration to provide 5mg/kg/min, and 20% fat emulsion to provide the remaining required calories. Thus, caloricdistribution is: AA-10%, CHO-30-40%, and FAT-50-60%. The amountof fat required to provide required calories may be excessive and should therefore be started at 1/4 to 1/2 of the final requirement.
Prescription for pediatric nutrition varies,depending upon underlying disease or disorder and metabolic rate,as well as variations in body composition. In general it is appropriate to start at reduced requirements, monitor clinical and chemical progress, and advance feeding as indicated and as tolerated.
email: pschloer@kumc.edu
(Predictions are subject to variations due to disease, race, and extremes of weight)
DISCLAIMER: Recommendations are subject to clinical confirmation.No responsibility is assumed by the authors, nor by the University of Kansas Medical Center.