Acidosis is a common and deleterious aspect of maintenance dialysis. Traditionally, it is considered to be an elevated anion gap
acidosis caused by the inability to excrete nonvolatile
anions. Stewart's approach made it possible to identify real determinants of the
acid-base status and allowed quantification of the components of these disturbances, especially the unmeasured
anions. We performed a cross-sectional study to identify and quantify each component of
acidosis in
hemodialysis maintenance patients. Sixty-four maintenance
hemodialysis patients and 14 controls were enrolled in this study. Gasometrical and biochemical analysis were performed before the midweek dialysis session. Quantitative physicochemical analysis was carried out using the Stewart methodology.
Hemodialysis patients were found to have mild acidemia (mean pH: 7.33 +/- 0.06 versus 7.41 +/- 0.05) secondary to
metabolic acidosis (serum
bicarbonate: 18.8 +/- 0.26 versus 25.2 +/- 0.48 mEq/l). The
metabolic acidosis was due to retention of unmeasured
anions (6.5 +/- 0.29 versus 3.1 +/- 0.62 mEq/l), hyperchloremia (105.1 +/- 0.5 versus 101.8 +/- 0.7 mEq/l), and
hyperphosphatemia (5.90 +/- 0.19 versus 3.66 +/- 0.14 mg/dl). Compared with control values, the unmeasured
anions and hyperchloremia had a similar acidifying effect (3.4 and 3.3 mEq/l), corresponding to almost 90% of the
metabolic acidosis. Unmeasured
anions and hyperchloremia are important components of
acidosis in maintenance
hemodialysis, in addition to
phosphorus. Future studies to determine the etiology and consequences of hyperchloremic
acidosis are warranted.