Impact of peritoneal membrane transport characteristics on acid-base status in CAPD patients

Abstract

Objective: To evaluate the role of individual peritoneal membrane transport characteristics on buffer balance through the peritoneal membrane, and thus on the final acid-base status. Design: Cross-sectional assessment of peritoneal membrane transport characteristics and acid-base status in continuous ambulatory peritoneal dialysis (CAPD) patients. Setting: Peritoneal dialysis unit in tertiary university hospital. Patients: The study included 143 clinically stable patients maintained on CAPD more than 6 months using 40 mmol/L of lactate-based dialysate. Main Outcome Measure: Comparison of acid-base status based on arterial blood gas analysis, dialytic lactate gain, bicarbonate loss, and total base gain according to membrane transport characteristics as defined by dialysate/plasma creatinine ratio (D/P(Cr)) of standard peritoneal equilibration test (PET). Results: Mean arterial bicarbonate concentration was 24.5 ± 3.5 mmol/L (16.2-35.7 mmol/L) and mean dialytic base gain was 29.3 ± 16.7 mmol/day. Only 15 (10.5%) patients showed metabolic acidosis, while 44 (30.8%) patients had various degrees of metabolic alkalosis. Distribution of peritoneal membrane characteristics in our subject showed the highest prevalence of low average (n = 66, 46.2%), followed by high average (n = 54, 37.8%), low (n = 13, 9.1%), and high (n = 10, 6.9%) transporters. The 4-hour D/P(Cr) was positively correlated with dialytic albumin loss, lactate gain, dialytic base gain, arterial pH, and bicarbonate concentration. Lactate gain and dialytic base gain were significantly higher in high transporters, which resulted in increased pH (7.4 ± 0.03 vs 7.38 ± 0.03, p < 0.05) and bicarbonate level (26.7 ± 3.2 vs 23.4 ± 2.8 mmol/L, p < 0.05) compared to patients with a low transport rate. Multiple regression analysis revealed that lactate gain, duration of peritoneal dialysis, CRP and normalized protein equivalent of nitrogen appearance were the independent factors determining the arterial bicarbonate level. Conclusion: The peritoneal membrane transport characteristics can be one of the important factors determining the acid-base status of peritoneal dialysis patients. Duration of dialysis, protein catabolic rate, and acute phase responses of patients also influence arterial bicarbonate level independently. Prospective long-term follow-up studies evaluating the potential role of membrane transport characteristics on acid-base stutus will be needed to further ascertain the clinical implication of this relationship.