Peritoneal Dialysis
Principles and prescription
Peritoneal dialysis uses the peritoneum as a semipermeable membrane. Solute removal occurs by diffusion down concentration gradients; water removal occurs by osmosis, chiefly from dextrose in the dialysate. Understand continuous ambulatory peritoneal dialysis (multiple daytime dwells) versus automated peritoneal dialysis (cycler-driven nighttime exchanges). Prescription variables include dwell volume, dwell time, number of exchanges, and dextrose concentration. Longer dwells favor solute equilibration but reduce ultrafiltration; higher dextrose increases ultrafiltration but also glucose absorption.
Assessing adequacy and membrane function
Use peritoneal equilibration testing to classify transport status: high transporters lose ultrafiltration with long dwells and may need shorter dwells; low transporters need longer dwells. Track total clearance including residual kidney function, which matters greatly and should be preserved. Monitor fluid balance, blood pressure, and weight.
Complications and traps
Peritonitis is the key infectious complication: cloudy effluent, abdominal pain, fever; send effluent for cell count and culture and treat per protocol, often with intraperitoneal antibiotics. Also recognize exit-site and tunnel infections, catheter malfunction, hernia, hydrothorax, and sclerosing encapsulating peritonitis. Trap: assuming cloudy effluent is benign or waiting for fever. Trap: forgetting that hyperglycemia and hypertriglyceridemia can result from dextrose absorption. Trap: not adjusting antibiotic dosing for the intraperitoneal route.
Worked example and rule of thumb
A patient on automated peritoneal dialysis reports cloudy bags and abdominal discomfort. Obtain effluent cell count and culture, begin empiric intraperitoneal therapy per protocol, and assess technique. Rule of thumb: cloudy effluent equals peritonitis until proven otherwise, and every ultrafiltration problem should prompt a check of transport status, dwell time, and dextrose concentration.