Summary

Renal Replacement Therapy (RRT) replaces the non-endocrine functions of the kidney (filtration of toxins, fluid removal, acid-base balance) in patients with Acute Kidney Injury (AKI) or End Stage Renal Disease (ESRD). The three modalities are Haemodialysis (HD), Peritoneal Dialysis (PD), and Transplantation.

• Haemodialysis: Extracorporeal circuit. Hospital based (usually).
• Peritoneal Dialysis: Intracorporeal. Home based.
• Transplantation: Definitive treatment. Best outcomes. [1,2]

Clinical Pearls

The "AEIOU" of Acute Dialysis: When to pull the trigger in AKI?

• Acidosis: pH < 7.15 (despite bicarbonate).
• Electrolytes: Hyperkalaemia (K > 6.5) refractory to medical Rx.
• Intoxication: Lithium, Salicylates, Ethylene Glycol.
• Overload: Pulmonary Oedema refractory to diuretics.
• Uraemia: Pericarditis or Encephalopathy (Urea > 30-50).

Fistula First: The AV Fistula is the "Lifeline". NEVER let anyone take blood, measure BP, or insert a cannula in a fistula arm. Preservation of arm veins (cephalic) in pre-dialysis patients is crucial.

Magnesium: In dialysis patients, Magnesium is often overlooked but important for preventing cramps and arrhythmias.

1. Diffusion (Clearance)

• Movement of solutes from high concentration (blood) to low concentration (dialysate) across a semi-permeable membrane.
• Removes small molecules (Urea, Creatinine, Potassium).
• Used in HD and PD.

2. Convection (Haemofiltration)

• Water is pushed across the membrane by hydrostatic pressure, dragging solutes with it ("Solvent Drag").
• Removes larger molecules (cytokines).
• Used in CVVH (ICU).

3. Ultrafiltration (Fluid Removal)

• Removal of water.
• HD: Achieved by hydrostatic pressure (suction) on the dialysate side.
• PD: Achieved by osmotic pressure (Glucose in the bag pulls water out).

Procedure

• Blood pumped out -> Heparin added -> Dialyser -> Air trap -> Returned to patient.
• Regimen: Usually 4 hours, 3 times a week.

Vascular Access

1. Arteriovenous Fistula (AVF): Gold Standard.
   • Anastomosis of Radial Artery to Cephalic Vein (Radio-Cephalic).
   • "Thrill" (Buzzing sensation) and "Bruit" (Machinery murmur) confirm patency.
   • Maturation: 6-8 weeks.
2. Arteriovenous Graft (AVG): Synthetic tube. Clots more easily.
3. Tunnelled Central Line (Permcath):
   • Internal Jugular Vein. Plastic tube with dacron cuff.
   • High risk of infection and central vein stenosis. Last resort.

Pros/Cons

• Pros: Efficient. Nurse-led (less patient responsibility). Social contact in unit.
• Cons: "Washout" post-dialysis (fatigue). Hypotension. Strict fluid/diet restrictions.

Procedure

• Tenckhoff Catheter inserted into peritoneal cavity.
• Exchange: Fluid infused (2L) -> Dwells (4-6 hours) -> Drained out.
• CAPD: Manual exchanges 4x day.
• APD: Machine cycler does exchanges at night while sleeping.

Physiology

• Membrane: The peritoneum.
• Osmotic Agent: Glucose (Dextrose). Higher concentration = More fluid removed (but more metabolic cost).

Complications

• Peritonitis: Bacterial entry. Cloudy bag, Abdo pain.
  • Organisms: Staph epidermidis (Skin), Staph aureus.
  • Rx: Intraperitoneal Vancomycin/Gentamicin.
• Hernias: Due to increased intra-abdominal pressure.
• EPS (Encapsulating Peritoneal Sclerosis): "Cocooning" of bowel. Rare, fatal.

Types

1. Living Donor: Best survival.
   • Related (HLA match likely).
   • Unrelated (Spouse/Altruistic).
2. Deceased Donor:
   • DBD (Brain Death): Better, as heart never stops beating.
   • DCD (Circulatory Death): Warm ischaemia time impacts function.

Immunosuppression

• Triple therapy standard: Tacrolimus + Mycophenolate + Prednisolone.

Outcomes

• Living Donor: Half-life ~15-20 years.
• Deceased Donor: Half-life ~10-15 years.
• Significantly lower cardiovascular mortality than dialysis.

        ESRD APPROACHING
        (eGFR < 20)
                ↓
    EDUCATION & MODALITY CHOICE
      ┌─────────┼─────────┐
 TRANSPLANT     PD        HD
 (WORKUP)    (HOME)    (UNIT)
      ↓         ↓         ↓
 LIVE DONOR?  INSERT    CREATE
 LISTING      TUBE     FISTULA
      ↓         ↓         ↓
  SURGERY     START     START
             DIALYSIS  DIALYSIS

Dialysis Disequilibrium Syndrome

• New HD patients. Rapid urea removal causes cerebral oedema (water rushes into brain).
• Prevention: Start slow (short sessions, low blood flow).

Dialysis Amyloid

• Accumulation of Beta-2 Microglobulin (not cleared well by dialysis).
• Causes Carpal Tunnel Syndrome and shoulder pain.

Access Complications

• Steal Syndrome: Fistula "steals" blood from the hand -> Cold, painful digits.
• Stenosis/Thrombosis: Loss of thrill. Needs plasty.

• Cardiovascular Disease: The leading cause of death in dialysis patients (10-20x general population hazard). Calcium/Phosphate imbalance causes rapid vascular calcification.
• 5-Year Survival: Transplant (90%) >> PD/HD (~50%).

Key Guidelines

Landmark Evidence

1. IDEAL Study (NEJM 2010)

• Showed no benefit to starting dialysis early (eGFR >10) vs waiting for symptoms (eGFR ~7). "Start late" is safe.

What is Dialysis?

When kidneys fail, they stop cleaning the blood. Poisons and water build up. Dialysis is a way of cleaning the blood artificially.

Haemodialysis (The Blood Machine)

• You go to hospital 3 times a week for 4 hours.
• Two needles are put into a "fistula" (a strong vein in your arm).
• Blood goes through a filter and comes back clean.
• Only good for cleaning toxins; it doesn't make hormones (so you still need EPO injections for anaemia).

Peritoneal Dialysis (The Tummy Tube)

• You have a soft tube permanently in your tummy.
• You run special water in, leave it for 4 hours, and drain it out. The water sucks the poisons out of your blood through your tummy lining.
• You do this at home, either 4 times a day or at night with a machine.

Is a Transplant a cure?

It is the closest thing to a cure. It gives you freedom from machines and diet restrictions. However, you are swapping one disease (Kidney Failure) for another (Immunosuppression). You must take pills for life to stop your body rejecting the new kidney.

Common Exam Questions

1. Indication: "ECG with broad QRS, K+ 7.2?"
   • Answer: Urgent Haemodialysis (after medical stabilization).
2. PD Complication: "Cloudy bag + tenderness?"
   • Answer: Peritonitis.
3. Access: "Why examine the fistula?"
   • Answer: To check patency (thrill) and infection (redness).
4. Physiology: "How is fluid removed in PD?"
   • Answer: Osmosis (Glucose gradient).

Viva Points

• Fistula vs Graft: Fistula is your own vein (lasts longer, fewer infections). Graft is plastic (clots easier, gets infected).
• Why do dialysis patients itch?: Uraemia and High Phosphate.
• Renal Bone Disease: High Phosphate + Low Calcium + High PTH = Bones dissolve. Treat with Phosphate Binders (Sevelamer) and Vitamin D (Alfacalcidol).

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.