Figure 1811

Amino acids in nutrition of acute renal failure (ARF): Conditionally essential amino acids. Because of the altered metabolic environment of uremic patients certain amino acids designated as nonessential for healthy subjects may become conditionally indispensable to ARF

patients: histidine, arginine, tyrosine, serine, cysteine [19]. Infusion of arginine-free amino acid solutions can cause life-threatening complications such as hyperammonemia, coma, and acidosis.

Healthy subjects readily form tyrosine from phenylalanine in the liver: During infusion of amino acid solutions containing phenylalanine, plasma tyrosine concentration rises (circles) [22]. In contrast, in patients with ARF (triangles) and chronic renal failure (CRF, squares) phenylalanine infusion does not increase plasma tyrosine, indicating inadequate interconversion.

Recently, it was suggested that glutamine, an amino acid that traditionally was designated non-essential exerts important metabolic functions in regulating nitrogen metabolism, supporting immune functions, and preserving the gastrointestinal barrier. Thus, it can become conditionally indispensable in catabolic illness [23]. Because free glutamine is not stable in aqueous solutions, dipeptides containing glutamine are used as a glutamine source in parenteral nutrition. The utilization of dipeptides in part depends on intact renal function, and renal failure can impair hydrolysis (see Fig. 18-10) [24]. No systematic studies have been published on the use of glutamine in patients with ARF, and it must be noted that glutamine supplementation increases nitrogen intake considerably.

Protein requirements

Urea nitrogen appearance (UNA) (g/d) = Urinary urea nitrogen (UUN) excretion + Change in urea nitrogen pool = (UUN x V) + (BUN2 - BUN1) 0.006 x BW + (BW2 - BW1) x BUN2/100

If there are substantial gastrointestinal losses, add urea nitrogen in secretions:

= volume of secretions x BUN2

Net protein breakdown (g/d) = UNA x 6.25

V is urine volume; BUN1 and BUN2 are BUN in mg/dL on days 1 and 2 BW1 and BW2 are body weights in kg on days 1 and 2

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