A variety of formulae are used by clinicians to estimate calorie requirements in hospitalized obese patients. Many of these formulae have been validated by determining their correlation to calorie requirements as determined by indirect calorimetry (IC). The use of correlation coefficients (CC) in this manner may be misleading. A more appropriate statistical methods, limits of agreement (LA), for comparing clinical measurements has recently been described by Bland and Altman. We obtained a total of 188 IC measurements on 113 obese (> 120% IBW), mechanically ventilated patients. These were compared by CC and LA to seven formulaic methods of determining calorie requirements. All formulae correlate significantly with IC. Analysis by LA indicated acceptable bias in several formulae (eg, 21 kcal/kg, Ireton-Jones obese patients (IJ), Ireton-Jones ventilatory patients, (VEE); however, the uniform lack of precision demonstrated by all formulae renders their clinical utility questionable.
The TNA system of nutritional support has become very popular and offers some unique advantages over the traditional method of administering TPN to hospitalized and home patients. However, these advantages as outlined in this review, must be carefully weighed against potential disadvantages before the TNA system is employed as a nutritional support modality. It should also be noted that the stability of TNA systems is not well established since many stability studies do not provide specific information regarding formulations tested. In addition, many studies do not utilize methods to determine the entire spectrum of particle size and distribution. Droplet size in TNA systems attain a diameter several times larger than the 0.2 to 0.4 micron of manufacturer's lipid emulsions and naturally occurring chylomicrons. Although the administration of the TNA system has not been associated with any acute toxicity, the long-term consequences of infusing droplets larger than 0.4 micron is not definitely known. In addition, the biological implications of using the TNA system need to be elucidated. Subtle differences in the properties of the lipid emulsion can affect the way it is metabolized by the body. Wretlind has mentioned that two apparently similar soybean oil emulsions, Intralipid, and Lipofundin are handled differently by the body. Minor differences in the phospholipid layer of the droplets were postulated as a cause. Certainly the nature of the emulsifying layer of phospholipid on TNA system droplets is modified and therefore may be metabolized differently. The recent report of enhanced growth of microorganisms in TNA systems is also worrisome.(ABSTRACT TRUNCATED AT 250 WORDS)
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