Peritoneal Dialysis Technique
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Direct answer
Peritoneal dialysis uses the patient's own peritoneum (about 1-2 square metres of visceral and parietal membrane with its capillary network) as the dialysis membrane: dialysate is instilled through a Tenckhoff catheter into the abdominal cavity, dwells while glucose osmotically pulls water and solutes cross the capillary endothelium, and is drained and discarded. Continuous ambulatory PD (CAPD) is manual — typically four 2-litre exchanges a day — while automated PD cyclers run overnight. Adequacy is judged by a weekly Kt/V of at least 1.7, and the modality's defining emergency is peritonitis: cloudy effluent with an absolute neutrophil count above 100 per microlitre, treated with intraperitoneal antibiotics.
What you must remember
- Physiology: diffusion across the peritoneal capillary bed plus osmotic ultrafiltration from glucose (1.5, 2.5 and 4.25 per cent dextrose strengths; icodextrin for the long dwell in high transporters).
- Access: the Tenckhoff catheter — a silicone tube with a Dacron cuff, tunnelled, exiting below the umbilicus; deep cuff on the preperitoneal fascia, exit site dressed and inspected daily.
- CAPD prescription: typically 2 litres per exchange, 4 exchanges daily (adjust for size and transport type), each cycle of fill (5-10 min), dwell (4-6 hours), drain (15-20 min).
- Adequacy: weekly Kt/V at least 1.7 (higher than the haemodialysis per-session figure because it is summed across the week) plus clinical wellbeing and fluid balance.
- Peritonitis — the examinable triad: cloudy effluent, abdominal pain, fever; diagnosis needs effluent white cell count over 100/microlitre with more than 50 per cent neutrophils; empirical intraperitoneal therapy commonly covers gram-positives (vancomycin or first-generation cephalosporin) and gram-negatives (ceftazidime or aminoglycoside) per ISPD guidance.
- Other complications: exit-site and tunnel infection, catheter malfunction (migration, omental wrap), hernias, leaks, hyperglycaemia and weight gain, protein loss (5-15 g/day), and ultrafiltration failure in long-term patients.
- Contraindications: extensive abdominal adhesions, recent abdominal surgery with drains, abdominal wall infection, severe respiratory compromise, and inability to perform aseptic technique.
- Assessment tool: the peritoneal equilibration test (PET) classifies the membrane from low to high transporter and tailors dwell times and solution strength.
Teaching a first CAPD exchange
Teach the exchange as a ritual, because the ritual is the prophylaxis. Hands washed to the elbow, mask on, a clean dedicated area, the minicap disconnected under no-touch technique: the patient drains until the abdomen is empty (time it — a slowing drain reports catheter malfunction before it becomes an emergency), weighs or eyeballs the effluent for cloudiness, then fills with 2 litres of 1.5 per cent dextrose warmed to body temperature, and caps. The whole cycle buys four to six hours of clearance and a few hundred millilitres of osmotic ultrafiltration, and repeats four times daily — which is precisely why PD offers steady biochemistry without needles, machines or a hospital chair.
The emergency drill deserves equal rehearsal. Cloudy effluent, even without fever, is peritonitis until the cell count says otherwise: send the effluent immediately, start empirical intraperitoneal antibiotics (fast-exchange loading dose per unit protocol), and culture — in Indian units Staphylococcus aureus remains the leading organism, with culture-negative cases common after antibiotic exposure. Meanwhile examine the exit site (purulence means tunnel involvement and a harder course), confirm the drain, and remember that refractory peritonitis, fungal peritonitis or refractory tunnel infection is the standard answer to "when is the catheter removed?"
How the exam frames it
Allied and Dialysis Technology papers alternate between numbers and emergencies. The numbers: 2 litres × 4 exchanges, weekly Kt/V 1.7, glucose strengths 1.5/2.5/4.25 per cent, effluent cell count above 100 with over half neutrophils. The emergencies: cloudy effluent (first step — cell count and empirical IP antibiotics, never "wait for culture"), and ultrafiltration failure (think PET re-testing, icodextrin for the long dwell, and glucose absorption in high transporters). A favourite comparison asks why PD suits diabetics less well metabolically (glucose load, weight gain) yet suits children and remote patients better (needle-free, home-based, fewer hospital visits) — and a viva may end on India-specific reality: PD penetration remains low despite lower infrastructure costs, limited by patient confidence, technique-loss and reimbursement structure.
Frequently asked questions
What defines peritonitis in a CAPD patient?
Cloudy effluent with an absolute neutrophil count above 100 per microlitre (over 50 per cent neutrophils), with or without abdominal pain and fever.
What is the standard CAPD prescription?
About four exchanges of 2 litres daily with dwell times of 4-6 hours, individualised by size, residual function and peritoneal transport type.
How is peritoneal dialysis adequacy measured?
By a weekly Kt/V of at least 1.7, together with fluid balance, nutrition and biochemical targets — a lower per-treatment bar than HD because clearance accrues continuously.
Which glucose strength is used for ultrafiltration in high transporters?
A long dwell with icodextrin (glucose polymer) or 4.25 per cent dextrose when glucose is absorbed too fast; the PET guides the choice.
Name absolute contraindications to peritoneal dialysis.
Extensive peritoneal adhesions, uncorrected abdominal wall defects or infection, recent abdominal surgery with drains, and inability to perform aseptic exchanges.