Peritoneal Dialysis and Peritonitis
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Direct answer
Peritoneal dialysis uses the patient's peritoneum as the dialyser, with dialysate exchanged through a catheter in CAPD or APD cycles. Its main complication is peritonitis, diagnosed by two of three features: cloudy effluent, a white cell count above 100 per microlitre with over 50 per cent neutrophils, or a positive culture. Empirical treatment is intraperitoneal vancomycin with a third-generation cephalosporin.
What you must remember
- Principle: solutes clear by diffusion across the peritoneum, and fluid is removed by osmosis, usually from glucose in the dialysate.
- Modalities: CAPD uses manual exchanges, often four a day, while APD uses an overnight cycler.
- Icodextrin: a glucose polymer used in long dwells to maintain ultrafiltration when glucose-based dialysate fails.
- Peritonitis definition: two of three features, which are clinical signs such as cloudy effluent or abdominal pain, a white cell count above 100 per microlitre with over 50 per cent neutrophils after a dwell of at least two hours, or a positive culture.
- Commonest organisms: coagulase-negative staphylococci, followed by Staphylococcus aureus and Gram-negative bacilli.
- Empirical therapy: intraperitoneal vancomycin with a third-generation cephalosporin such as ceftazidime, adjusted when culture results return.
- Catheter removal: indicated for fungal peritonitis, refractory infection, relapsing or recurrent peritonitis and refractory tunnel or exit-site infection.
- Quality target: the ISPD 2022 goal is no more than 0.40 episodes per year at risk, and older texts quote 0.5.
A man on CAPD with cloudy fluid and abdominal pain
A 60-year-old man on CAPD for two years has abdominal pain and cloudy effluent after an overnight dwell. His exit site looks clean, and he is otherwise well.
- Send the effluent first: The dialysate is sent for cell count with differential, Gram stain and culture, ideally before any antibiotic is given into the peritoneal cavity.
- Confirm the diagnosis: Cloudy effluent with a white cell count above 100 per microlitre and neutrophils above 50 per cent meets two of the three criteria, which is enough to diagnose peritonitis.
- Start empirical antibiotics: Intraperitoneal vancomycin and a third-generation cephalosporin are given at once, covering both Gram-positive and Gram-negative organisms.
- Examine the exit site and tunnel: Redness, tenderness or discharge at the catheter exit is looked for, since a tunnel infection changes management.
- Narrow therapy by culture: Antibiotics are adjusted when culture results return, usually within two to three days.
- Judge the response: Failure to improve within about five days is treated as refractory peritonitis, which prompts review of the catheter.
- Remove the catheter when needed: Fungal peritonitis, refractory infection or relapsing peritonitis or refractory tunnel infection calls for catheter removal and temporary haemodialysis.
Where the examiner tests the diagnosis
Most errors come from diagnosing peritonitis on one feature or from keeping the catheter when it must come out.
- Trap: diagnosing peritonitis from cloudy effluent alone Correct: the ISPD definition needs two of three features, so the cell count and culture are required to confirm.
- Trap: giving only systemic antibiotics for PD peritonitis Correct: the intraperitoneal route delivers high concentrations directly where the infection lies, and it is the preferred route.
- Trap: keeping the catheter in fungal peritonitis Correct: Candida peritonitis usually needs catheter removal and antifungal therapy, since antibiotics alone fail.
Frequently asked questions
What are the ISPD criteria for peritonitis in peritoneal dialysis?
Peritonitis is diagnosed when at least two of three features are present: clinical signs such as cloudy effluent or abdominal pain, a dialysate white cell count above 100 per microlitre with more than 50 per cent neutrophils after a dwell of at least two hours, or a positive culture.
Which organism commonly causes peritoneal dialysis peritonitis?
Coagulase-negative staphylococci are the commonest organisms causing peritoneal dialysis peritonitis, followed by Staphylococcus aureus and Gram-negative bacilli. The organism profile guides the choice of definitive therapy once culture results return.
Why is intraperitoneal antibiotic therapy preferred in peritoneal dialysis?
Intraperitoneal antibiotics deliver high concentrations directly into the dialysate, where the infection lies, which is why this route is preferred. Empirical therapy usually combines intraperitoneal vancomycin with a third-generation cephalosporin such as ceftazidime.
When is catheter removal indicated in peritoneal dialysis peritonitis?
Catheter removal is indicated for fungal peritonitis, refractory peritonitis that fails to improve within about five days, relapsing or recurrent infection, and refractory tunnel or exit-site infection. Patients usually need temporary haemodialysis while the catheter is out, and a new catheter is considered later.
What does cloudy effluent in peritoneal dialysis indicate?
Cloudy effluent is the most common presentation of peritonitis in peritoneal dialysis, reflecting white cells and debris in the drained fluid. It is a clinical criterion only, so a cell count and culture are needed to confirm the diagnosis.