PERITONEUM STRUCTURE AND FUNCTION IN PERITONEAL DIALYSIS

basics peritoneum

1. PERITONEUM IN PD

2. Anatomy of peritoneal cavity surface area ranges from 1 – 2 m² visceral peritoneum accounts for about 80% of the total peritoneal surface area. superior mesenteric artery, and venous drainage is via the portal system. The parietal peritoneum is more important in peritoneal dialysis. receives blood from the lumbar, intercostal, and epigastric arteries and drains into the inferior vena cava.

3. Histology of peritoneum The peritoneal membrane is lined by a monolayer of mesothelial cells equipped with microvillae . Underlying the mesothelium is the interstitium , which comprises a gel-like matrix, the peritoneal capillaries, and some lymphatics.

4. Three pore model 6 regions of resistance to moving solute and water across the peritoneum (a) the stagnant capillary fluid film overlying the endothelium of the peritoneal capillaries, (b) the capillary endothelium itself, (c) the endothelial basement membrane, (d) the interstitium , (e) the mesothelium, and ( f) the stagnant fluid film that overlies the mesothelium.

5. Distribution model The “effective peritoneal surface area”. Area of the peritoneal surface that is sufficiently close to the peritoneal capillaries to play a role in transport.

6. Physiology of peritoneal transport (a) diffusion, (b) ultrafiltration, and (c) fluid absorption. Diffusion depends on Concentration gradient Effective peritoneal surface area Intrinsic peritoneal membrane resistance Molecular weight of the solute Mass transfer area coefficient Peritoneal blood flow

7. Ultrafiltration Osmotic gradient between the dialysis solution and the peritoneal capillary blood - due to the presence of high concentrations of glucose in the dialysis solution Depends on Concentration gradient for the osmotic agent (e.g., glucose). Effective peritoneal surface area Hydraulic conductance of peritoneum Reflection coefficient of the osmotic gradient Hydrostatic pressure gradient Oncotic pressure gradient Sieving

8. Fluid absorbtion Intraperitoneal hydrostatic pressure Lymphatics

9. Peritoneal equilibration test 2-L of 2.5% dextrose is instilled in peritoneal cavity dwell with dialysate samples taken at 0, 2, and 4 hours and a plasma sample at 2 hours. D/P Cr, D/P Urea, D/P Na, are estimated after 4 hours. Net fluid removal (volume drained at 4 hours vs. volume instilled) and the ratio of dialysate glucose at 4 hours to dialysate glucose at time zero (D/D0 G)are also estimated

10. Four “transporter” categories: High transporters - relatively large effective peritoneal surface area and/ or high intrinsic membrane permeability. Low transporters, in contrast, have slower and less complete equilibration for urea and creatinine, reflecting low membrane permeability and/or small effective peritoneal surface area. High-average and low-average transporters have intermediate values for these ratios and for ultrafiltration and protein losses