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Discussion of Protein Requirements and Nitrogen Balance


- See:
   - Glutamine
   - Arginine
- Nitrogen Balance = Nitrogen Input - Nitrogen Output
    Nitrogen Out = (Urinary Urea * 0.85) + 4 gm/dl
- Nitrogen Balance can be calculated by the Kjeldahl technique, or urea content can be measured and the result / 0.85; Nitrogen content of the TPN solution = 6.5 gm N / lit;
- Note that Nitrogen Balance calculations are inaccurate in Burns, Fistula, or Diarrhea
    - Obligatory loss of 10 - 15 gm of Nitrogen lost daily in the Urine
    - Each gm of Nitrogen represents 6.25 gm of muscle protein
    - Hence loss of 60-90 gm of protein qd;
- Discussion:
    - dose of exogenous amino acid or protein is increased until nitrogen equilibrium is achieved;
    - further increases in the amino acid load appear only to enhance ureagenesis and azotemia, but not to improve nitrogen balance;
    - when standard amino acid preparations are given in dosages sufficient to meet this oxidative rate, result is excessive availability of gluconeogenic aminoacids often in setting of existent hyperglycemia & excess of aromatic aminoacids, the level of which is thought to correlate with hepatic insufficiency;
    - high branched chain amino acid formulae contain 45-50% branched chain amino acids, with concomitantly decreased amounts of gluconeogenic and aromatic amino aids, where as standard amino acid formulations contain 15-33% branched chain amino acids


Inaccuracy of nitrogen balance determinations in thermal injury with calculated total urinary nitrogen.

The effect of stress level, amino acid formula, and nitrogen dose on nitrogen retention in traumatic and septic stress.

Glutamine-enriched intravenous feedings attenuate extracellular fluid expansion after a standard stress.