ACID-BASE-BALANCE IN CHRONIC PERITONEAL-DIALYSIS PATIENTS

Endogenous acid production has never been measured directly in dialysi s patients and an empiric formula is used to estimate acid production from their protein catabolic rate. We have studied acid-base balance i n 19 stable CAPD patients attending the peritoneal dialysis clinic of Mount Sinai Hospital. They obtained a 24 hour collection of peritoneal dialysis fluid and urine while consuming their usual diet and perform ing their usual activities. Total alkali gain was calculated from net GI alkali absorption plus urinary net acid excretion plus alkali gain from dialysate, while total acid production was measured directly from the urinary and dialysate excretions of sulfate and organic anions. N et GI alkali absorption was estimated from the difference between cati ons (Na + K + Ca + Mg) and anions (Cl + 1.8P) in the 24 hour dialysate and urine collections minus the daily total amount of lactate infused . All of our patients had a normal or high serum bicarbonate concentra tion, which was stable with time. Total alkali gain was virtually iden tical to total acid production (54.2 vs. 52.4 mEq/day) which suggests that these patients were in neutral acid-base balance. Net GI alkali a bsorption (22.7 mEq/day) was one of the same range as that of chronic renal failure patients not on dialysis and represented almost one half of the total daily alkali gain. The daily acid production of 52.4 mEq /day was numerically equal to 84% of the protein catabolic rate expres sed as g/day, which is similar to the predicted value of 77% of PCR re ported in the literature. However, the main source of alkali loss, tha t is, acid production, was the loss of organic anions in dialysate and urine. Daily sulfate excretion (16 mEq/day) was lower than expected f or the level of protein intake (protein catabolic rate of 62 g/day). T he stable serum bicarbonate concentrations on long-term dialysis sugge sts a steady state and neutral acid-base balance in these patients. Th e almost perfect agreement between acid production and total alkali ga in supports the validity of our methods for measuring the various para meters of acid-base balance, including net GI absorption of alkali.