What is CAPD?
CAPD stands for Continuous Ambulatory Peritoneal Dialysis, a form of renal replacement therapy for patients with end-stage renal disease (ESRD) or advanced chronic kidney disease (CKD). 1
Definition and Mechanism
CAPD is a continuous dialysis modality that uses the peritoneal membrane as a natural filter to remove waste products and excess fluid from the blood. 1 Unlike hemodialysis, which is performed intermittently (typically 3 times weekly for 3-4 hours), CAPD operates 24 hours per day, 7 days per week, providing steady-state solute and fluid removal. 1, 2
Key Characteristics
- Continuous therapy: Dialysate remains in the peritoneal cavity continuously, with exchanges performed multiple times daily by the patient. 1, 3
- Ambulatory nature: Patients perform exchanges themselves at home or work, allowing greater independence and mobility compared to in-center hemodialysis. 3, 4
- Peritoneal membrane utilization: The peritoneum acts as the dialyzing membrane, with solute removal occurring through diffusion and convection. 1
Clinical Application
CAPD is indicated for patients with CKD G5 (kidney failure) requiring renal replacement therapy. 1 The modality is particularly suitable for:
- Patients who prefer home-based therapy with greater autonomy. 3, 4
- Those with cardiovascular instability who cannot tolerate the rapid fluid shifts of hemodialysis. 5
- Pediatric patients, especially young children where vascular access is challenging. 5
- Patients in settings where hemodialysis resources are limited. 5, 6
Advantages Over Hemodialysis
- Better preservation of residual kidney function: Multiple studies demonstrate that CAPD preserves residual renal function significantly better than hemodialysis, which is critical for overall patient outcomes. 1
- Hemodynamic stability: Continuous fluid removal avoids the rapid volume shifts that occur with intermittent hemodialysis, reducing cardiovascular stress. 5, 4
- Steady-state biochemistry: Continuous therapy provides more stable control of uremia, electrolytes, and acid-base balance compared to the peaks and valleys of intermittent hemodialysis. 4
- Better control of hypertension and anemia: The continuous nature allows for superior management of volume status and blood pressure. 4
Dosing and Adequacy Targets
The adequacy of CAPD is measured using Kt/V (clearance × time / volume of distribution). 1
- Target weekly Kt/V: ≥2.0 per week, which includes both peritoneal clearance (Kpt/V) and residual renal clearance (Krt/V). 1
- Residual kidney function contribution: RKF can provide 30-50% of total solute clearance, especially in the first 2 years of therapy. 1
- Monitoring frequency: Kt/V should be measured within 6 months of initiation and regularly thereafter to ensure adequate dialysis delivery. 1
Major Complications and Pitfalls
- Peritonitis: This remains the most significant barrier to CAPD success, though incidence can be reduced with proper technique, bacterial filters, and appropriate patient selection. 3, 4
- Protein loss: Peritoneal protein losses can lead to hypoproteinemia and malnutrition in some patients, requiring careful nutritional monitoring. 1, 4
- Metabolic complications: Hyperlipidemia develops in approximately 50% of patients due to glucose absorption from dialysate, though dietary modification can help. 4
- Mechanical issues: Abdominal hernias and catheter-related problems may occur. 4
Survival Outcomes
- Five-year survival: Approximately 52-63% of ESRD patients on CAPD survive to 5 years, with 1-year and 3-year survival rates of 80% and 60%, respectively. 7
- Comorbidity impact: Patients with both hypertension and type 2 diabetes have significantly worse outcomes (hazard ratio 8.4) compared to those with hypertension alone. 7
Contemporary Nomenclature
Current KDIGO guidelines (2020) recommend using the term "CKD G5D" (chronic kidney disease, GFR category 5, treated by dialysis) rather than "ESRD" when describing patients on CAPD. 1 The term "kidney replacement therapy" (KRT) is preferred over "renal replacement therapy" (RRT). 1