Acid base correction in bicarbonate CAPD patients

Bicarbonate has been proposed as buffer in CAPD solutions in recent years instead of lactate and acetate. The present study is designed to evaluate peritoneal bicarbonate kinetics using bicarbonate solutions. Seventy kinetic studies have been performed in 7 patients treated with 2 CAPD solutions containing 35 mmol/l (A) and 27 mmol/l (B) of bicarbonate. The changes in dialysate bicarbonate concentration at different dwell times were correlated with bicarbonate blood levels. Furthermore after 2 hours of dwell time and at subsequent observations, no differences in dialysate bicarbonate concentration were found between A and B solutions at the same bicarbonatemia. Thus a feedback between bicarbonate absorption and bicarbonate blood concentration was observed. If the amount of bicarbonate transferred to the patient is over the metabolic acid production, bicarbonatemia will rise: consequently bicarbonate dialysate absorption will decrease. After a few days, an equilibrium point will be reached. In this condition the bicarbonate absorption is equal to metabolic acid production and, in stable clinical conditions, a stable acid base status will be maintained by the patient. Our studies empirically demonstrated that the equilibrium is reached when a difference of 5 mmols between blood and inlet dialysate bicarbonate concentration is observed. Consequently to achieve 25 mmol/l of bicarbonatemia, the bicarbonate concentration of CAPD solution should be about 30 mmol/l.