Metabolic acidosis in maintenance hemodialysis patients: clinical impact and intervention

Metabolic acidosis has been considered as one of the reverse epidemiologic factors for the morbidity and mortality in maintenance hemodialysis patients (MHP). Expectedly, in the recent large scale epidemiologic study (The Dialysis Outcome Practice Pattern Study, DOPPS), a mild to moderate degree of predialysis metabolic acidosis has shown better nutritional status and lower relative risk for mortality and hospitalization in MHP. Similarly, another recent study of the largest sample size of MHP of more than 55,000 revealed the lowest unadjusted mortality with mild to moderate degree of predialysis HCO3 levels (17 to 23 mEq/L). However, it was reversed after case-mix and multivariate adjustment, including the malnutrition-inflammation complex syndrome, so that predialysis HCO3 levels of more than 22 mEq/L had a lower death risk. On view of this up-to-date on-going controversy about the optimal acid-base status for MHP, this paper will review the historical and break-through data about the pros and cons of metabolic acidosis published in the clinical human studies of MHP, a special subgroup of chronic kidney disease patients. Based on these results, if possible, we would like to suggest the best practice guideline, particularly, for the optimal predialysis HCO3 level, dialysate HCO3 concentration, and dietary protein intake.