The use of amino acid based CAPD fluid in chronic renal failure

CAPD is a major treatment for end-stage renal disease. A dialysis fluid in the peritoneum, changed several times a day, uses glucose, an effective osmotic agent but which contributes to hyperlipidaemia and malnutrition. Amino acids have been investigated as an alternative to glucose in several short and long-term studies described in the literature. One to two % amino acids are maximally absorbed into blood after 2–4 h and decrease to initial concentrations after 6 h unless constituents are in excess e.g. phenylalanine and methionine. These changes and those for other metabolites are similar to a marked post-prandial effect. In several studies up to 12 weeks duration, one or two exchanges of 1% amino acids daily were well tolerated with modest nutritional improvement (e.g. in amino acids, transferrin or total body nitrogen), small decreases in hyperlipidaemia, with no clinical problems due to loss of appetite, increase in urea, overhydration or acidosis. Both these and less favourable studies suggest problems could occur with higher concentrations or multiple exchanges and also in unsuitable patients. Slight loss of ultrafiltration and increased protein losses into dialysate suggest a reversible effect on permeability. Our studies suggest that amino acid exchanges increase complement activation by the alternative pathway which with generation of prostaglandin E2, increases permeability. However, amino acids absorbed exceed all protein losses, although percentage utilisation is not known. Amino acid based fluids are unsuitable for patients on high protein or low calorie diets or those requiring more effective dialysis. Fluids containing increased buffering capacity and lower concentrations of certain amino acids are indicated.