Factors contributing to formation of edema in volume overloaded continuous ambulatory peritoneal dialysis patients.

BACKGROUND: Volume control is critical for the success of peritoneal dialysis (PD) but dry weight in PD has been difficult to obtain. Edema free is, in general, accepted clinically as a target for volume control in PD patients. However, PD patients can be free of edema despite significant volume overload. The present study investigates the possible factors that influence the formation of pitting edema in volume-overloaded PD patients.
METHODS: In this cross-sectional study, patients' fluid status was evaluated by multifrequency bioelectrical impedance spectroscopy analysis. Values for overhydration were obtained. Patients with overhydration ≥ 2.0 kg were considered volume overloaded and were eligible for inclusion. From 1 March 2009 to 1 December 2009, a total of 96 patients on continuous ambulatory PD were included. Endothelial function was evaluated by flow-mediated dilatation (FMD). Other clinical indicators, such as blood pressure, dialysis adequacy, nutrition status, and biochemical parameters, were recorded. Patients were divided into 2 groups based on edema status: the edema group (n = 35 volume-overloaded patients with bilateral pitting edema) and the non-edema group (n = 61 volume-overloaded patients without bilateral pitting edema).
RESULTS: Overhydration in the edema group was significantly higher than in the non-edema group (4.28 ± 1.75 kg vs 3.12 ± 0.81 kg, p < 0.001), whereas both FMD and serum albumin in the edema group were significantly lower than in the non-edema group (6.65% ± 5.2% vs 10.3% ± 5.1%, p = 0.001; 37.6 ± 4.2 g/L vs 39.3 ± 3.5 g/L, p = 0.047, respectively). Edema status (edema = 1, non-edema = 0) was positively correlated with overhydration (r = 0.341, p < 0.001), gender (male = 1, female = 2: r = 0.184, p = 0.072), and total fluid removal (r = 0.188, p = 0.074) and negatively correlated with endothelial function, as assessed by FMD (r = -0.33, p = 0.001), and serum albumin (r = -0.18, p = 0.055). Logistic regression analysis showed that FMD [odds ratio (OR) 0.90, 95% confidence interval (CI) 0.81 - 0.99; p = 0.036], gender (male = 1, female = 2: OR 4.06, 95% CI 1.23 - 13.35; p = 0.021), overhydration (OR 3.06, 95% CI 1.53 - 6.13; p = 0.002), and serum albumin (OR 0.86, 95% CI 0.75 - 0.99; p = 0.035) were independent factors affecting the edema status of the study population.
CONCLUSION: Our study showed that endothelial function (assessed by FMD), gender, serum albumin, and overhydration are independent determinants of edema status in PD patients. This may explain why some PD patients can maintain free of edema despite significant volume overload.