FACTORS AFFECTING BICARBONATE TRANSFER WITH BICARBONATE-CONTAINING CAPD SOLUTION

Objective: To evaluate bicarbonate fluxes across the peritoneal, membr ane and bicarbonate gain in patients treated with continuous ambulator y peritoneal dialysis (CAPD) using dialysis solutions with different b icarbonate concentrations. Patients and Design: Ninety-seven exchanges , using different dwell times and glucose and bicarbonate concentratio ns were performed in 43 stable CAPD patients. Dialysate effluent bicar bonate concentration and volumes were measured at different dwell time s. Net dialytic bicarbonate gain was calculated. Patients' acid-base s tatus was determined at the middle of the dwell. Results: In prolonged dwells (6 - 12 hours)the dialysate effluent bicarbonate concentration correlated with arterial plasma bicarbonate concentration F = 129, p < 0.0001), but not with ultrafiltration rate or dialysis solution bica rbonate concentration. In 4-hour dwells, effluent bicarbonate concentr ation correlated with both plasma bicarbonate concentration and ultraf iltration rate (F = 32.52, p < 0.0001 and F = 4.4, p < 0.05, respectiv ely). The effluent bicarbonate concentration may be predicted from the patient's plasma bicarbonate concentration and net ultrafiltration ra te for either a 4-hour or prolonged (6 - 12 hours) dwell time. Net bic arbonate gain by the patient correlated with ultrafiltration rate, pla sma bicarbonate, and dialysis solution bicarbonate concentration (F = 100.56, p < 0.0001 at 4 hours and F = 108.08, p < 0.0001 at 6 - 12 hou rs), with the ultrafiltration rate being the predominant parameter. Co nclusions: The effluent bicarbonate concentration is related to plasma bicarbonate concentration, with ultrafiltration playing a marginal ro le only during short dwells. However, the ultrafiltration rate has a p rofound effect on net patient bicarbonate gain. Multiple linear regres sion analysis allows the prediction of the effect of acid-base status, ultrafiltration, dwell time, and dialysis solution bicarbonate conten t on net patient bicarbonate gain. It seems that bicarbonate content i n the CAPD dialysis solution should be progressively increased with in creasing solution osmolality.