Acid-base Balance of Korean CAPD Patients: Incidence of Metabolic Acidosis and Factors Affecting the Acid-base Status

Kang, Duk Hee; Lee, Ho Yung; Han, Dae Suk; Kim, Yong Soo; Bang, Byung Kee; Yoon, Kyun Il

Abstract

OBJECTIVES: Any form of dialysis must provide a sufficient replenishment of buffer. Lactate with a con- centration of 35 to 40mM/L is now the only buffer routinely used in CAPD. Buffer balance using lactate solutions will be governed essentially by the balance between the H+ generated, the amount of bicarbonate lost into the peritoneal effluent, and the lactate absorbed from the dialysate. Factors affecting buffer balance in CAPD patients will therefore include dietary protein intake which determine H+ generation and ultrafiltration which can affect bicarbonate loss. Although several studies reported a different prevalence of metabolic acidosis in their CAPD patients, it is uncertain whether the same prevalence of metabolic acidosis(MA) or the similar characteristics of acid-base status of Western CAPD patients can be found in Asian patients with smaller body size and relatively less amount of dietary animal protein intake. This study was undertaken to know the current acid-base status of CAPD patients in Korea with the exact information about buffer balance. We will also investigate the factors affecting acid-base homeostasis in CAPD patients such as dietary protein intake, the individual membrane characteristics and the various indices of dialysis adequacy and nutritional status of patients. METHODS: The acid-base status of Korean CAPD patients was assessed based on arterial blood gas analysis along with various nutritional parameters including subjective global assessment(SGA), anthropometric measurements and standard peritoneal equilibration test in 198 clinically stable patients main- tained on CAPD for more than 6 months using 35- 40mM/L of lactate-based dialysate(M:F 106:92, mean age 47.9 years, mean duration 45.3 months). RESULTS: Mean arterial bicarbonate concentration was 24.6+/-3.4mM/L with a range of 16.2-36.7mM/L and mean dialytic base gain was 29.4+/-15.2mM/day. Only 28(14.1%) patients showed MA while 52(26.3%) patients had a various degree of metabolic alkalosis. Normal acid-base status was observed in 75 patients(37.9%). The rest showed mixed acid-base abnormalities of respiratory origin. Patients with MA (mean HCO3 19.5+/-1.9mM/L) showed significantly higher serum albumin(4.01+/-0.38 vs. 3.59+/-0.46 g/dl, P<0.001) & protein equivalent of nitrogen appearance (NPNA, 1.2+/-0.1 vs. 0.9+/-0.2 g/kg/day, P<0.05) compared to the metabolic alkalosis group(mean HCO3 28.1+/-1.9mM/L). Dialytic protein loss(6.39+/-1.86 vs. 7.64+/-2.71 g/day, P<0.01) and D/PCr(0.60+/-0.09 vs. 0.71+/-0.13, P<0.05) were significantly lower in MA group. There were no significant differences in residual renal function, KT/VUrea, number of malnourished patients by SGA and other anthropometric parameters according to the acid-base status of patients. There were significant inverse correlations of arterial HCO3 with serum albumin and NPNA while HCO3 was positively correlated with duration of dialysis, ultrafiltration volume, dialytic lactate gain and dialytic protein loss. CONCLUSION: Our results on the acid-base status of Korean CAPD patients including a generally lower incidence of MA appear to be quite different from other reports based on the Western population. The peritoneal membrane transport characteristics can be one of the important factors determining the acid- base status of peritoneal dialysis patients. Duration of dialysis and protein catabolic rate also influence arterial bicarbonate level independently.