Effect of increased dialysate volume on peritoneal surface area among peritoneal dialysis patients

Large dialysate volumes are often required to increase solute clearance for peritoneal dialysis patients. The resulting increase in solute clearance might be attributable to an increased plasma-to-dialysate concentration gradient and/or to an increased effective peritoneal surface area. One of the factors affecting the latter is the peritoneal surface area in contact with dialysate (PSA-CD). The aim of this study was to estimate the change in PSA-CD after a 50% increase in the instilled dialysate volume for patients undergoing peritoneal dialysis. PSA-CD was estimated by using a method applying stereologic techniques to computed tomographic (CT) scans of the peritoneal space. The peritoneal cavity of 10 peritoneal dialysis patients was filled with a solution containing dialysate, half-isotonic saline solution, and contrast medium. Peritoneal function tests and CT scanning of the abdomen were performed twice for each patient (with an interval of 1 wk), after instillation of a 2- or 3-L solution. Scanning of thin helical CT sections was performed, and 36 random sections of the abdomen were obtained after reconstruction. A grid was superimposed on the sections. The surface area was estimated by using stereologic methods. After instillation of the 2-L solution, the volume of the peritoneal solution at the time of CT scanning was 2.32 ± 0.05 L. The PSA-CD was 0.57 ± 0.03 m², ranging from 0.41 to 0.76 m². The use of the 3-L solution increased the peritoneal volume by 46 ± 2%. PSA-CD increased by 18 ± 2.3% to 0.67 ± 0.04 m² (range, 0.49 to 0.84 m²; P < 0.01). Creatinine mass transfer increased from 112 ± 10 mg to 142 ± 11 mg (P < 0.0001). The slope of the change of the plasmato-dialysate creatinine concentration gradient with time decreased from -2.26 ± 0.23 × 10^-2 to -1.97 ± 0.16 × 10^-2 (P = 0.01). K_BD-0 (permeability-surface area product or mass area transfer coefficient at time 0 of the dwell) increased from 10.6 ± 0.7 to 13.6 ± 1.2 ml/min (P < 0.02). These data demonstrate that increasing the instilled dialysate volume by 50% for peritoneal dialysis patients results in significant increases in the PSA-CD and K_BD.