Automated Peritoneal Dialysis (APD)

What is APD?

APD Apparatus (Equipment)

The APD Cycler Machine

Key brands include Baxter (HomeChoice/Amia series) and Fresenius Medical Care (Sleep•Safe / Newton IQ). Both offer digital card technology for remote data transmission.

The Peritoneal Access Catheter (Tenckhoff Catheter)

• Made of silicone rubber or polyurethane
• Most common design: double-cuff, swan-neck, coiled Tenckhoff catheter
  • The coiled intraperitoneal tip sits near the pouch of Douglas (prevents migration, reduces infusion pain)
  • Inner cuff anchors in the rectus abdominis muscle (prevents leaks)
  • Outer cuff sits in subcutaneous tissue (acts as a barrier against exit-site infection)
  • Swan-neck design keeps the exit site pointing downward/laterally (reduces cuff extrusion and infection)

Diagram: Peritoneal Dialysis Setup

Catheter Insertion Procedure

1. Fluoroscopic + Ultrasound Technique (Interventional Nephrology)

1. Abdomen prepped and draped in sterile fashion; conscious sedation given (midazolam + fentanyl)
2. Insertion site: 2 cm left or right and below the umbilicus
3. A 21-gauge needle guided under ultrasound (5-12 MHz transducer) through: skin → subcutaneous tissue → rectus fascia → rectus muscle → inner fascia → parietal peritoneum
4. 3-5 mL radiocontrast injected under fluoroscopy to confirm peritoneal placement (outer bowel delineation pattern)
5. A 0.018-inch cope-mandrel wire inserted through the needle; needle exchanged for a 6-French catheter sheath
6. 2 cm skin incision made; subcutaneous tissue digitally dissected to rectus muscle
7. Serial dilators (8, 12, 14-French) passed over stiff glide-wire; 18-French peel-away sheath placed
8. Double-cuff swan-neck Tenckhoff catheter introduced over glide-wire; coiled tip placed in lower abdominal cavity
9. Inner cuff pushed into rectus muscle; tunnel created with exit site distal, lateral, and below the incision
10. Final fluoroscopic image taken to verify placement
11. Inflow/outflow tested with 500 mL normal saline; catheter flushed with 10-15 mL heparin
12. Wound sutured and dressed
13. Catheter NOT used for 10-14 days to allow healing; PD usually started 2-4 weeks post-insertion

2. Peritoneoscopic Technique (Y-TEC)

3. Surgical / Laparoscopic Technique

APD Treatment Procedure (Each Session)

Setup (Before Bed)

1. Wash hands thoroughly; prepare a clean work surface
2. Connect 10-15 liters of dialysis solution bags to the cycler tubing/cassette
3. Load the cassette into the cycler
4. Program the cycler with the prescribed settings: fill volume, number of cycles, dwell time, total therapy duration
5. Connect the patient line to the peritoneal catheter using aseptic technique

The Cycler Cycle - Three Phases

Initial Drain (I-Drain)
     ↓
┌──────────────────────────────────┐
│  FILL     → Dialysate pumped     │
│             into peritoneal      │  × Repeated
│             cavity               │  several
├──────────────────────────────────┤  cycles
│  DWELL    → Fluid dwells; waste  │  overnight
│             and fluid cross      │
│             peritoneal membrane  │
├──────────────────────────────────┤
│  DRAIN    → Used dialysate       │
│             pumped to effluent   │
│             bag                  │
└──────────────────────────────────┘
     ↓
Last fill (optional daytime dwell)
     ↓
Disconnect in the morning

1. Initial Drain - cycler first empties any existing fluid from the peritoneal cavity
2. Fill phase - fresh dialysate (warmed to body temperature) flows into the abdomen via the patient line; cassette pumps measure exact fill volume
3. Dwell phase - fluid remains in the cavity for a set time; uremic toxins (urea, creatinine) and excess water diffuse across the peritoneal membrane into the dialysate by osmosis/diffusion
4. Drain phase - used dialysate pumped out into effluent bag; ultrafiltrate volume calculated
5. Cycle repeats 4-6 times over 8-12 hours
6. Last fill (optional) - the final bag of fresh dialysate may be left in the abdomen as a daytime dwell ("wet day"), or the patient disconnects with an empty abdomen ("dry day") - depends on prescription

Modes of APD

Prescription Parameters

• Fill volume (typically 1.5-3 L per cycle)
• Number of exchanges (usually 3-6 per night)
• Dwell time per cycle
• Total therapy duration (8-12 hours)
• Dialysate concentration (glucose 1.5%, 2.5%, or 4.25% - higher glucose = more fluid removal by osmosis)

Key Advantages of APD over CAPD

• Exchanges happen during sleep - daytime is free for work/activities
• Reduced risk of peritonitis (fewer manual connections during the day)
• Automated measurement of ultrafiltration volumes
• Remote data monitoring via digital card / cloud-based systems (healthcare team can review treatment data between visits)

References

• Brenner and Rector's The Kidney (9780323532655), Chapter 68: Peritoneal Dialysis - Catheter Procedures, pp. 2914-2916
• Automated cyclers used in peritoneal dialysis - PMC/NIH
• Mayo Clinic - Peritoneal Dialysis

Intermittent Peritoneal Dialysis (IPD)

Overview

IPD has largely fallen out of favor for chronic ESKD due to concerns about inadequate small solute clearance, replaced by more efficient APD/CCPD techniques. - Merck Manual - Peritoneal Dialysis

Diagram 1: IPD Apparatus Setup - Tenckhoff Catheter and Gravity Drainage

• Left panel: Cross-section of the Tenckhoff catheter passing through skin, fat, muscle, and peritoneum with two Dacron cuffs securing it in place
• Right panel: The classic IPD gravity setup - dialysate bag hung on an IV pole flows downward by gravity into the peritoneal cavity; effluent drains by gravity into a collection bag below the patient

Diagram 2: Anatomical Overview of Peritoneal Dialysis Access

Apparatus

1. Peritoneal Access Catheter

2. Dialysate Solution

• Composition: Glucose-based (1.36%, 2.27%, or 3.86% glucose) or icodextrin; buffered with lactate or bicarbonate; contains electrolytes (Na⁺, Ca²⁺, Mg²⁺, Cl⁻)
• Volume: 2-3 L per exchange in adults; 30-40 mL/kg in children
• Temperature: Warmed to 37°C before infusion (prevents pain and vasoconstriction)
• Packaging: Supplied in sterile PVC bags (1.5 L, 2 L, 2.5 L, 3 L)

3. Delivery System

• Performs all exchanges at night
• Fully drains the peritoneal cavity at the end of the session (dry day)
• No fluid left in the abdomen between sessions

Diagram 3: The Three Phases of One IPD Exchange

FILL PHASE (10-15 min)
┌────────────────────────────────────────────────────┐
│  Dialysate bag (hanging high) → gravity or pump    │
│  Fresh 2-3 L dialysate flows into peritoneal       │
│  cavity via Tenckhoff catheter                     │
└────────────────────────────────────────────────────┘
              ↓
DWELL PHASE (30-40 min)
┌────────────────────────────────────────────────────┐
│  Clamps closed; fluid dwells in peritoneum         │
│  Uremic toxins (urea, creatinine, K⁺) diffuse     │
│  across peritoneal membrane into dialysate         │
│  Excess water removed by osmosis (glucose gradient)│
└────────────────────────────────────────────────────┘
              ↓
DRAIN PHASE (10-15 min)
┌────────────────────────────────────────────────────┐
│  Drain clamp opened; effluent flows by gravity     │
│  (or pump) into collection bag below patient       │
│  Peritoneal cavity left COMPLETELY EMPTY (dry)     │
└────────────────────────────────────────────────────┘
              ↓
Cycle repeated multiple times (typically 8-24 cycles)

IPD Procedure - Step by Step

Preparation

1. Patient is positioned supine or reclined (recumbency improves drainage)
2. Dialysate bags warmed to 37°C (water bath, dry warmer, or cycler heater bag)
3. Hands washed thoroughly; sterile field prepared
4. Catheter exit site inspected for signs of infection
5. Transfer set spiked onto dialysate bag aseptically; tubing primed to remove air

Exchange Technique (Manual Gravity)

1. Clamp the drain line and open the fill line
2. Hang dialysate bag on IV pole above patient level
3. Allow 2-3 L to infuse over 10-15 minutes by gravity
4. Close fill line when bag is empty
5. Patient may move gently to distribute fluid across the peritoneum
6. Dwell for 30-40 minutes (clamps closed)
7. Open drain line; lower drain bag below patient level
8. Drain over 10-15 minutes - peritoneal cavity fully emptied
9. Measure effluent volume - compare to fill volume to calculate ultrafiltration
10. Inspect effluent: should be clear/straw-colored (cloudy = suspect peritonitis)
11. Disconnect drain bag; attach fresh dialysate bag for next exchange
12. Repeat cycle as prescribed

Session Duration and Frequency

• Acute IPD (AKI): Multiple exchanges over 12-48 hours continuous; can extend to 72 hours if needed
• Chronic IPD: Historically 3 sessions per week, each lasting 10-14 hours (20-24 exchanges per session); done in hospital/outpatient dialysis unit
• NIPD (Nocturnal IPD - modern variant): Exchanges overnight (8-10 hours) via cycler; cavity left dry during the day; typically every night or 5-6 nights per week

Comparison of IPD Variants

Incremental IPD (Starting PD)

• Start with 2-3 overnight exchanges at 1.5 L fill volume per exchange
• As RKF declines, increase fill volumes by 20-30% increments (up to max 2.5 L)
• If more clearance needed: increase number of exchanges
• Eventually add a daytime dwell (converts NIPD → CCPD/APD)

Monitoring During IPD

Advantages and Limitations of IPD

Advantages

• Simple to set up and perform
• Effective for AKI (no need for systemic anticoagulation unlike hemodialysis)
• Safe in hemodynamically unstable patients
• Lower infection risk vs CAPD (fewer daytime connections)
• NIPD variant allows a free daytime schedule

Limitations

• Inadequate clearance in anuric/oliguric patients (dry day = no continuous dialysis)
• Not recommended for chronic ESKD patients without RKF
• Less efficient than CAPD or CCPD for solute removal
• Requires hospital/clinic attendance (classic IPD)
• Patient remains recumbent during session

References

• Brenner and Rector's The Kidney (9780323532655), Chapter 64: Frequency of Exchanges, p. 2787
• Comprehensive Clinical Nephrology, 7th Edition (9780323825924), Chapter 13: Prescribing Incremental PD, p. 1323
• Merck Manual - Peritoneal Dialysis
• PMC - Automated cyclers in peritoneal dialysis
• Fresenius Liberty Cycler User's Guide (IPD mode description)