Metabolic acidosis and composite nutritional index (CNI) in CAPD patients

Metabolic acidosis (MA) has been recognized as an important stimulus for net protein catabolism. Continuous ambulatory peritoneal dialysis (CAPD) is regarded to have advantage in normalizing the acid-base homeostasis over hemodialysis due to continuous supply of buffer. However, many CAPD patients still remain acidotic and the clinical impact of this MA is uncertain. Recent studies revealed no specific correlation between a certain degree of MA and protein nutritional status while others showed that mild alkalosis is nutritionally beneficial to CAPD patients. A cross-sectional study evaluating acid-base and nutritional status was performed to examine the relationship between acid-base status and overall nutritional status assessed by composite nutritional index (CNI) and to get a basic information about the optimal pH/HCO3 in CAPD patients.

Total 198 clinically stable patients maintained on CAPD more than 6 months were evaluated. Each of 10 nutritional parameters of CNI consisting of clinical (subjective global assessment), biochemical (total lymphocyte count, albumin, prealbumin, insulin-like growth factor-1, transferrin) and anthropometric parameters (body mass index, % lean body mass, triceps skinfold thickness, midarm muscle circumference) was graded from 0 to 3 point (0; normal, 1; mildly decreased, 2; moderately decreased, 3; severely decreased).

Mean CNI score was 8.2 +/- 5.2 with a range of 0 to 25. CNI was positively correlated with age, duration of peritoneal dialysis, incidence of peritonitis, C-reactive protein (CRP), HCO3 and dialytic protein loss whereas it was inversely correlated with hemoglobin and nPNA. In patients with MA (n = 25, mean arterial HCO3 19.5 +/- 1.9 mM/l), CNI score was significantly lower (6.3 +/- 3.5) compared to patients with normal acid-base status (n = 63, 9.5 +/- 5.9, p < 0.01) or metabolic alkalosis (n = 47, 10.1 +/- 4.6, p < 0.001). Multiple regression analysis revealed that the incidence of peritonitis, duration of dialysis, CRP and dialytic protein loss were the independent predictors of CNI.

CAPD patients with mild to moderate degree of MA appear to be associated with more favorable overall nutritional status expressed as CNI. Prospective studies evaluating changes in the nutritional parameters with the correction of acid-base abnormality are needed to understand the real impact of acid-base status on nutritional status and to know the optimal pH/HCO3 in CAPD patients.