Introduction

Comparison of Peritoneal Dialysis and Haemofiltration

Peritoneal Dialysis:

• Cheaper.
• Utilizes a biocompatible membrane.
• Provides cardiovascular stability.
• Does not require vascular access.
• Avoids the need for anticoagulation.
• No specialized equipment or nursing required.
• Facilitates more rapid recovery of renal function compared to haemodialysis.
• Allows easy transition to long-term PD.

Haemofiltration:

• Greater control over ultrafiltration rate.
• Suitable for patients who have undergone laparotomy.

Solute Removal and Fluid Removal in Peritoneal Dialysis

Solute Removal Mechanisms:

• Diffusion: Selective movement of small solutes (e.g., potassium, urea, creatinine) down a concentration gradient across a semipermeable membrane.
  • Example: Like tea diffusing from a tea bag into water.
• Convection: Non-selective movement of larger molecules (e.g., proteins) with water, also known as solute drag.
  • Example: Squeezing a tea bag forces tea out with water.

Process:

• Dialysis fluid is instilled into the abdominal cavity, where small solutes move from serum into the peritoneal fluid due to concentration gradients.
• Water moves into the peritoneal cavity by osmosis, dragging larger molecules with it.
• Replacing equilibrated dialysis fluid with fresh solution is necessary to maintain the concentration gradient.

Fluid Removal Mechanism:

• Achieved by osmosis, driven by glucose in the PD fluid.
  • Higher glucose concentration increases fluid removal.
  • Prolonged dwell times result in glucose diffusion back into the patient, reducing osmotic gradient and causing fluid reabsorption.
• Increased fluid removal requires higher glucose concentrations or shorter cycle times (minimum one hour).
• Solutes such as urea, creatinine, phosphate, and glucose reach equilibrium at different rates during PD.
• Urea equilibrates most rapidly, followed by creatinine, phosphate, and β₂-microglobulin. Glucose concentration in dialysate decreases over time due to diffusion into the serum.

Peritoneal Membrane Structure

• Mesothelium:
  • Protective barrier with villous projections, increasing the membrane surface area (~20m²).
  • No role in solute flow regulation.
• Interstitium: Connective matrix maintaining membrane integrity.
• Capillaries: Serve as the semipermeable membrane for solute and water exchange.

Devices for Peritoneal Dialysis

Rigid Catheter:

• Plastic catheter inserted subumbilically.
• Advantages:
  • Easy insertion.
  • Requires minimal training.
  • Cost-effective.
• Disadvantages:
  • Narrow lumen leading to slow dialysate flow and frequent blockages.
  • Higher risk of leakage, hemorrhage, and peritonitis.
  • Should only be used if flexible catheters are unavailable.

Flexible Tenckhoff Catheter:

• Made of silastic with Dacron cuffs, available in straight or coiled designs.
• Inserted via a percutaneous or surgical approach.
• Advantages:
  • Higher efficiency and fewer complications compared to rigid catheters.
  • Tunneling under the skin reduces leakage and infection risks.
• Contraindications for percutaneous insertion include:
  • Midline surgical scars.
  • Previous abdominal tuberculosis.
  • Complex appendectomy or cholecystectomy.

Dialysis Prescription in AKI

Key Considerations:

1. Fluid Overload:
   • Use 3.86% glucose solution for pulmonary edema or severe fluid overload.
   • Use more frequent fluid exchanges for higher fluid removal.
2. Hyperkalaemia/Acidosis:
   • Corrected by increasing the frequency of fluid exchanges.
3. Dehydration:
   • Use 1.36% glucose solution.

Cycle Time:

• Minimum one hour to maximize effective dialysis time.

Evidence For Peritoneal Dialysis in AKI

• Studies from Brazil and India indicate comparable urea clearances to intermittent haemodialysis, with earlier recovery of renal function in PD patients (e.g., by 3 days).
• Cytokine clearance may be greater with PD, though evidence is limited.

Anaesthesia and Surgical Techniques for PD Catheter Insertion

General Anesthesia (GA):

• Induction:
  • Propofol: 1–2 mg/kg intravenously.
  • Fentanyl: 1–2 µg/kg intravenously.
  • Cisatracurium: 0.15 mg/kg intravenously for tracheal intubation.
• Maintenance:
  • Oxygen and air with either:
    • Sevoflurane or Desflurane: Titrated to an age-adjusted Minimum Alveolar Concentration (MAC) of 0.8–1.1.

Local Anesthesia (LA):

• Sedation:
  • Initiated after applying monitors.
  • Midazolam: 0.015 mg/kg intravenously.
  • Fentanyl: 1–2 µg/kg intravenously.
  • Remifentanil (optional): 0.01–0.1 µg/kg/min infusion.
  • Propofol: Administered as:
    • Intermittent boluses of 10–20 mg.
    • Continuous infusion at 25–150 µg/kg/min.
  • Titrated to maintain a sedation level of 3–4 on the Observer’s Assessment of Alertness/Sedation (OAA/S) scale.
• Supplemental Oxygen: Delivered via facemask to all patients.
• Hemodynamic Fluctuations: Managed with small doses of vasopressors or vasodilators.

Surgical Technique:

• Local Anesthesia: Achieved using 1% lidocaine to infiltrate the soft tissue and peritoneum.
• Pneumoperitoneum:
  • Nitrous Oxide (N₂O): Used for LA group.
  • Carbon Dioxide (CO₂): Used for GA group.
  • Insufflation pressure: Maximum of 12 mmHg.

Postoperative Care:

• All patients were transported to the Post-Anesthesia Care Unit (PACU) for monitoring following surgery.

Key Points from Comparative Studies of LA vs. GA

• LA Group:
  • Shorter procedure and recovery times.
  • Lower perioperative risk for high-risk patients.
  • Equivalent PACU scores on discharge compared to GA.
• GA Group:
  • Necessary for more complex cases with prior abdominal surgery or need for extensive adhesiolysis.

Both techniques are safe and effective, with nearly 45% of patients being suitable for LA.

Links

Renal replacement therapy

ICU and renal disease

References:

1. Liu X, Zuo X, Heng X, Abreu Z, Penner T, et al. (2017) Anesthesia Considerations for Insertion of the Peritoneal Dialysis Catheter. J Clin Nephrol Ren Care 3:028. doi.org/10.23937/2572-3286.1510028
2. Maio R, Figueiredo N, Costa P (2008) Laparoscopic placement of Tenckhoff catheters for peritoneal dialysis: a safe, effective, and reproducible procedure. Perit Dial Int 28: 170-173.](https://www.ncbi.nlm.nih.gov/pubmed/18332453)
3. Manouras AJ, Kekis PB, Stamou KM, Konstadoulakis MM, Apostolidis NS (2004) Laparoscopic placement of Oreopoulos-Zellerman catheters in CAPD patients. Perit Dial Int 24: 252-255.](https://www.ncbi.nlm.nih.gov/pubmed/15185773)

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