Peritoneal Dialysis
Core concepts
Peritoneal dialysis uses the peritoneal membrane as the dialyzer. Dextrose in the dialysate creates an osmotic gradient that pulls water across the membrane; solute moves by diffusion and, over time, by convection. The prescription rests on fill volume (commonly 2.0–2.5 L), dwell time, and number of exchanges.
CAPD is manual, typically four exchanges daily with 4–6 hour dwells. APD uses a cycler overnight with shorter dwells, often with a final daytime dwell. A peritoneal equilibration test (PET) classifies membrane transport: high transporters absorb glucose quickly, lose the osmotic gradient, and need short dwells plus icodextrin to avoid fluid overload; low transporters need longer dwells to reach adequate clearance.
Peritonitis is the signature complication: cloudy effluent, abdominal pain, fever, nausea. Send the first drained bag for cell count and culture; the diagnosis is effluent leukocytes >100/mm³ with >50% neutrophils. Start intraperitoneal antibiotics promptly. Refractory, relapsing, or fungal peritonitis means catheter removal.
Trap: outflow failure is usually constipation, not catheter failure. Ask about bowel movements and treat with a laxative before escalating. A cloudy bag is never normal - culture it even if the patient feels well.
Worked example: a CAPD patient drains 1.2 L net from a 2.5 L fill and has 2+ edema. Rather than raising dextrose concentration in every exchange, review the PET: if transport is high, shorten dwells and consider icodextrin for the long dwell.