The effect of hemodialysis on electrolytes and acid-base parameters.

BACKGROUND: Hemodialysis patients are treated with bicarbonate dialysate to correct the metabolic acidosis, which results from the metabolism of dietary and endogenous protein. The concentration of plasma tCO(2) is used to gauge the success of therapy. Reported low values in pre-dialysis blood suggest incomplete correction of acidosis in a substantial percent of the dialysis population. However, questions have been raised about the reliability of tCO(2) determination in dialysis patients.

METHODS: Pre- and post-dialysis blood specimens were obtained from chronic hemodialysis patients and analyzed on-site using an OPTI Critical Care Analyzer. Results were compared with reports obtained monthly from the reference laboratory to which the samples were routinely shipped for analysis. In addition, OPTI analyzer whole blood electrolytes were compared with plasma electrolytes determined in a local laboratory.

RESULTS: Mid-week testing of patients dialyzed against a 40-mmol/l bicarbonate dialysate found that most patients had normal acid-base status pre-dialysis and frank metabolic alkalosis by the end of dialysis. Whole blood tCO(2) values determined on the OPTI CCA were 2.4 mmol/l greater than heparin plasma tCO(2) assayed on the Vitros chemistry analyzer. Small differences were also observed for K(+) and Cl(-).

CONCLUSIONS: Based on our on-site determination of acid-base and electrolyte concentrations, metabolic acidosis appears to be fully correctable in well-dialyzed renal failure patients. Metabolic alkalosis is apparent in the post-dialysis period.