Acid-Base Status During the Interdialytic Period in Patients Maintained with Chronic Hemodialysis

The changes in blood pH, PCO2, and plasma bicarbonate were evaluated during the interdialytic period in 16 studies of 14 patients with chronic renal failure treated with maintenance hemodialysis. Arterial pH levels rose in all patients at the end of dialysis, and in half the patients frank alkalemia (pH > 7.46) was observed within the first 24 hr. The mean PCO2 values were low (less than 36 mm Hg) and did not vary significantly throughout the entire period of observation. There was an increase in plasma bicarbonate in all patients; plasma bicarbonate levels were highest at the end of dialysis in eight studies, whereas in the remaining eight the peak bicarbonate value occurred 6 to 12 hr after completion of dialysis. These results indicate that a constant hyperventilatory state exists during the entire interdialytic period in most patients. The rise in plasma bicarbonate with the sustained hyperventilation underlies the alkalemia. The data further suggest that there may be a delay in acetate metabolism in some of the patients treated with chronic hemodialysis.