The peritoneal membrane in peritoneal dialysis patients: estimation of its functional surface area by applying stereologic methods to computerized tomography scans.

The surface area of the peritoneal membrane in contact with dialysate is an important determinant of solute transport across the peritoneum. Yet there is no method for its estimation in peritoneal dialysis patients. In this study, stereologic methods were applied to computerized tomography (CT) imaging of the peritoneal membrane to estimate the peritoneal membrane surface area. The method was first validated by implementing stereologic methods on a phantom of known surface area. The phantom was a distorted bottle filled with contrast media. Series of thin helical CT sections were performed, and random sections were obtained after reconstruction. A transparent counting grid was placed over the random sections. The surface area was estimated using 9, 18, and 36 random sections. To calculate the coefficient of variation (CV) of the method, 20 different combinations of 9, 18, and 36 random sections were used. With 36 random sections, the error in estimation of the bottle's surface area was -9.4% to +8.8%. The CV was 5.0%. Decreasing the number of sections used to 18 and 9 yielded a CV of 7.8 and 12.3%, respectively. This method was then applied to the peritoneal membrane, which was visualized by instilling dialysate containing contrast media into the peritoneal cavity of peritoneal dialysis patients. The estimated peritoneal membrane surface area of six patients was 0.55 +/- 0.04 m2. This novel method permits the measurement of the peritoneal membrane surface area with a high degree of accuracy.