Pre and interdialytic acid-base balance in hemodialysis patients.

In an observational study, nine hemodialysis patients using 35 mmol/l bicarbonate dialysate were studied over a 44-hour interdialytic interval. Serum bicarbonate was measured at regular intervals at home and the mean time averaged concentration was 27.0+/-1.2 mmol/l. Seven of the nine patients showed a slow linear decline in bicarbonate whilst in two patients levels were unchanged. In 8 of 9 patients the average of the post and predialysis bicarbonate accurately predicted the time-averaged (area under the curve) bicarbonate concentration. In addition, predialysis serum bicarbonate was measured in 46 patients after both a 2 and 3-day interdialytic interval. The serum bicarbonate was significantly lower after the 3-day interdialytic interval (3-day, 22.1+/-0.6 vs 2-day, 23.0+/-0.5 mmol/l, p<0.05). The results from this study emphasize the importance of standardization of bicarbonate measurement in order to avoid spurious acidosis.