Renal replacement therapy

Surgical approach (when RRT requires a procedure)

• RRT itself is not an operation; procedures relate to establishing access (vascular access or peritoneal access)
• Temporary haemodialysis/CRRT access (vascath)
  • Ultrasound-guided cannulation: usually right internal jugular (preferred), femoral, or left IJV; subclavian generally avoided (stenosis risk for future AV fistula)
  • Large-bore double-lumen catheter inserted using Seldinger technique; tip position: SVC/RA junction (IJV) or IVC (femoral)
  • Asepsis, tunnelling optional (longer-term), securement and dressing; confirm position and exclude complications (CXR for IJV/subclavian)
• Long-term haemodialysis access
  • AV fistula creation (radiocephalic, brachiocephalic, brachiobasilic transposition) or AV graft if vessels unsuitable
  • Avoid venepuncture/arterial lines/BP cuffs on fistula arm; protect access perioperatively
• Peritoneal dialysis (PD) access
  • Surgical or laparoscopic placement of Tenckhoff catheter into peritoneal cavity; tunnelled subcutaneously with exit site
  • Potential adjuncts: omentopexy, adhesiolysis; test fill/drain intra-op

Anaesthetic management (procedures related to RRT access)

• Temporary dialysis catheter (ICU/ED/theatre)
  • Type of anaesthesia: local anaesthetic infiltration ± light sedation; GA rarely required (uncooperative, severe agitation, paediatrics, complex access)
  • Airway: usually none; if deep sedation/GA then ETT; SGA possible but aspiration risk often higher in uraemia/critical illness
  • Duration: typically 15–45 min
  • Pain: mild–moderate (skin + deep tissue dilation); ensure adequate LA and analgesia
  • Key anaesthetic issues: haemodynamic instability, coagulopathy/anticoagulation, positioning, oxygenation/ventilation, sepsis, raised urea/platelet dysfunction
• AV fistula/graft formation
  • Type of anaesthesia: regional (brachial plexus block) or GA; regional may improve fistula blood flow via sympathectomy and avoid GA in comorbid patients
  • Airway: if GA, usually ETT; SGA may be acceptable for short superficial surgery if aspiration risk low
  • Duration: ~1–2.5 h
  • Pain: usually mild–moderate; regional provides excellent analgesia
  • Key issues: preserve veins (avoid cannulation on planned fistula side), fluid balance, potassium/acid-base, BP targets to maintain fistula perfusion, anticoagulants/antiplatelets
• Peritoneal dialysis catheter insertion
  • Type of anaesthesia: GA commonly (laparoscopic); open insertion may be possible under regional/LA with sedation in selected patients
  • Airway: ETT usually for laparoscopy; consider aspiration risk (uraemia, diabetes gastroparesis)
  • Duration: ~0.5–1.5 h
  • Pain: moderate (abdominal wall + peritoneal irritation); multimodal analgesia
  • Key issues: pneumoperitoneum effects, fluid restriction, electrolyte derangements, infection risk, postoperative nausea/vomiting

Definitions and aims

• RRT = extracorporeal or peritoneal therapies replacing kidney functions: solute clearance, volume control, acid–base and electrolyte homeostasis
• Aims in ICU: treat life-threatening complications (hyperkalaemia, pulmonary oedema), manage AKI with fluid overload, control uraemia, allow nutrition/drug dosing, manage severe acidosis
• Core mechanisms: diffusion (dialysis), convection (haemofiltration), ultrafiltration (fluid removal), adsorption (some membranes/filters)

Indications for initiating RRT (AKI/critical care)

• Common FRCA framework: AEIOU
  • A — Acidosis: severe metabolic acidosis refractory to medical therapy (e.g., pH ≤ 7.1–7.2 depending on context)
  • E — Electrolytes: refractory hyperkalaemia (esp. with ECG changes) ± severe hypermagnesaemia
  • I — Intoxications: dialysable toxins (e.g., lithium, salicylate, methanol, ethylene glycol, valproate in selected cases)
  • O — Overload: pulmonary oedema/volume overload refractory to diuretics; inability to achieve fluid balance
  • U — Uraemia: encephalopathy, pericarditis, bleeding, severe symptoms
• Other ICU triggers: persistent oliguria/anuria with rising urea/creatinine, severe dysnatraemias in selected contexts, temperature control (rare), cytokine removal is not an established indication

Modalities of RRT

• Intermittent haemodialysis (IHD)
  • Mechanism: mainly diffusion; high solute clearance over 3–5 h sessions
  • Pros: rapid K+ and toxin clearance; widely available; short treatment time
  • Cons: haemodynamic instability (rapid fluid/solute shifts), risk of dialysis disequilibrium, less suitable for raised ICP/unstable patients
• Continuous RRT (CRRT): CVVH, CVVHD, CVVHDF
  • CVVH (haemofiltration): convection (solute drag) with replacement fluid
  • CVVHD (haemodialysis): diffusion with dialysate
  • CVVHDF: combined diffusion + convection
  • Pros: better haemodynamic tolerance, gradual fluid removal, better control of acid–base/electrolytes, preferred in cerebral oedema/raised ICP
  • Cons: anticoagulation issues, circuit clotting, hypothermia, electrolyte depletion (phosphate), nursing/technical burden
• Sustained low-efficiency dialysis (SLED/SLEDD-f)
  • Hybrid: prolonged intermittent (6–12 h) with lower flow rates; improved haemodynamic tolerance vs IHD
  • Useful where CRRT resources limited; can be scheduled overnight
• Peritoneal dialysis (PD)
  • Mechanism: diffusion across peritoneal membrane; ultrafiltration via osmotic gradient (glucose-based dialysate)
  • Pros: no extracorporeal circuit/anticoagulation; useful in children, difficult vascular access; gentler haemodynamics
  • Cons: peritonitis, lower clearance in hypercatabolic ICU patients, impaired ventilation with large volumes, contraindicated in recent major abdominal surgery/adhesions (relative)

Principles: diffusion, convection, ultrafiltration

• Diffusion: solute movement down concentration gradient across semipermeable membrane; best for small molecules (urea, K+)
• Convection: solvent drag with ultrafiltration; better for middle molecules; requires replacement fluid (pre- or post-filter)
  • Pre-dilution replacement: reduces haemoconcentration and clotting but lowers solute clearance
  • Post-dilution: higher clearance but higher filter clot risk
• Ultrafiltration: fluid removal driven by transmembrane pressure; can be isolated (SCUF) for fluid overload

Vascular access for extracorporeal RRT

• Sites: right IJV (first choice), femoral, left IJV; avoid subclavian if possible (central venous stenosis jeopardises future AVF)
• Catheter characteristics: large bore, short and wide improves flow; double lumen; strict asepsis; ultrasound guidance reduces complications
• Complications: bleeding/haematoma, arterial puncture, pneumothorax/haemothorax, air embolus, arrhythmias (wire), infection, thrombosis, catheter dysfunction/recirculation

Anticoagulation strategies (CRRT/IHD)

• Why: blood–foreign surface contact activates coagulation; need to prevent circuit clotting while minimising bleeding
• No anticoagulation
  • Consider if high bleeding risk; accept shorter filter life; optimise access, blood flow, pre-dilution, saline flushes
• Unfractionated heparin (UFH)
  • Systemic anticoagulation; monitor APTT/anti-Xa; risks: bleeding, HIT, variable response in critical illness
  • Protamine reverses; consider in procedures/bleeding
• Regional citrate anticoagulation (RCA) (common in CRRT)
  • Mechanism: citrate chelates ionised calcium in circuit → inhibits coagulation; calcium is replaced systemically (separate infusion)
  • Monitoring: systemic ionised Ca2+, post-filter ionised Ca2+ (target low), total Ca2+/ionised Ca2+ ratio (citrate accumulation if rising, e.g. >2.5)
  • Complications: hypocalcaemia, metabolic alkalosis (citrate metabolised to bicarbonate), metabolic acidosis if citrate accumulates, hypernatraemia (some solutions), hypomagnesaemia
  • Risk factors for citrate accumulation: severe liver failure, shock with poor perfusion, hypothermia (impaired metabolism)
• Other anticoagulants (less common): LMWH, prostacyclin, direct thrombin inhibitors (argatroban) if HIT

Prescription variables (what you can change)

• Blood flow rate (Qb): affects clearance and filter life; too low increases clotting/recirculation
• Dialysate flow (Qd) (diffusion) and replacement flow (Qr) (convection): determine solute clearance
• Net ultrafiltration rate: determines fluid removal; set according to haemodynamics and overall fluid balance goals
• Effluent rate (CRRT dose surrogate): commonly prescribed ~20–25 mL/kg/h (delivered dose lower due to downtime); higher doses not shown to improve mortality routinely
• Dialysate composition: K+, Ca2+, bicarbonate/lactate buffer; adjust to patient needs (avoid rapid shifts)

Physiological effects and complications relevant to anaesthesia/ICU

• Haemodynamic instability
  • Causes: excessive ultrafiltration, vasodilation, myocardial stunning (IHD), sepsis, impaired autonomic responses
  • Management: reduce UF, fluid bolus if appropriate, vasopressors, consider CRRT/SLED instead of IHD
• Electrolyte and acid–base disturbances
  • Hypokalaemia, hypophosphataemia (common in CRRT), hypomagnesaemia; monitor and replace proactively
  • Citrate: hypocalcaemia and alkalosis; accumulation causes acidosis and rising total:ionised Ca ratio
• Temperature
  • Extracorporeal circuits can cool patient; use fluid warmers, warming blankets; hypothermia worsens coagulopathy and citrate metabolism
• Bleeding risk
  • Uraemic platelet dysfunction + anticoagulation; consider DDAVP, tranexamic acid (case-dependent), correct anaemia, avoid unnecessary anticoagulation
• Dialysis disequilibrium syndrome (DDS) (mainly IHD)
  • Mechanism: rapid urea removal → osmotic gradient → cerebral oedema; symptoms: headache, nausea, confusion, seizures, coma
  • Risk: first dialysis, very high urea, children, pre-existing CNS disease; prevention: slower/shorter dialysis, lower clearance, mannitol/hypertonic saline in selected cases
• Drug dosing and removal
  • Removal depends on: molecular weight, protein binding, volume of distribution, water solubility, membrane type, modality and dose (effluent rate), adsorption
  • Antibiotics often need supplemental dosing (e.g., beta-lactams, vancomycin) guided by levels where possible

Anaesthetic considerations in patients receiving RRT (perioperative)

• Preoperative assessment
  • Timing since last dialysis: aim for optimisation of volume status and K+; beware intradialytic hypotension and residual anticoagulation (heparin used during IHD)
  • Check: K+, bicarbonate/pH, Ca2+/phosphate, Hb, platelet count/function, coagulation, volume status, ECG, access sites (AVF/vascath/PD)
  • Comorbidities: IHD patients often have CAD, LVH, pulmonary oedema, autonomic neuropathy (diabetes), difficult airway (uraemic changes), gastroparesis
• Intraoperative management
  • Monitoring: consider arterial line for major surgery/unstable patients; avoid lines/BP cuff on fistula arm; protect dialysis catheters
  • Induction/maintenance: reduce doses for some agents due to altered protein binding and sensitivity; titrate to effect; consider haemodynamic lability
  • Neuromuscular blockade: avoid/limit agents dependent on renal excretion (e.g., pancuronium); prefer atracurium/cisatracurium; sugammadex use in ESRD is possible but complex—follow local guidance and consider prolonged complexation/excretion
  • Fluids: avoid overload; balanced crystalloids often acceptable; consider potassium content (Hartmann’s contains ~5 mmol/L K+ but usually safe in small volumes—context dependent); use goal-directed therapy
  • Vasopressors: often required; dialysis patients may be vasoplegic/autonomic neuropathy
• Postoperative considerations
  • Analgesia: avoid NSAIDs (AKI/bleeding); use opioids carefully (active metabolites accumulate: morphine, codeine); consider fentanyl/alfentanil/remifentanil intra-op; oxycodone/hydromorphone require caution; regional techniques useful
  • Plan for dialysis/CRRT restart: coordinate anticoagulation, haemostasis, and fluid balance; monitor K+ and acid–base closely

RRT and sepsis/critical illness: practical ICU points

• CRRT is often chosen in septic shock due to haemodynamic tolerance; however, it can clear antibiotics—dose adjust and use TDM where possible
• Common ICU problem: recurrent filter clotting—check access function, blood flow, filtration fraction (aim lower), anticoagulation adequacy, haematocrit, and interruptions
• Nutrition/electrolytes: CRRT removes amino acids, water-soluble vitamins, phosphate; anticipate supplementation