Aneurysm clipping

Surgical approach

• Usually pterional/frontotemporal craniotomy (common for anterior circulation aneurysms); other approaches (orbitozygomatic, interhemispheric, subtemporal, far-lateral) depending on aneurysm location
  • Head fixed in Mayfield pins, rotated/extended; microscope used
  • Dural opening → CSF drainage (cisternal opening) to relax brain; careful arachnoid dissection to expose aneurysm neck
• Temporary arterial occlusion may be applied (temporary clip) to facilitate dissection/clip placement
  • Risk: focal ischaemia; duration minimised; sometimes repeated temporary occlusions
• Definitive clip applied across aneurysm neck; patency of parent/branch vessels confirmed
  • Adjuncts: ICG angiography, micro-Doppler, intra-op DSA (centre dependent)
• Potential for sudden rupture during dissection/clip application → rapid blood loss, raised ICP, need for controlled hypotension/temporary occlusion
  • Brain swelling may require osmotherapy, hyperventilation, ventricular drainage, or decompression

Anaesthetic management (overview)

• Type of anaesthesia: General anaesthesia with controlled ventilation; neurophysiology monitoring may influence agent choice
  • TIVA (propofol/remifentanil) commonly used if MEP/SSEP monitoring; volatile acceptable in many cases at low MAC
• Airway: ETT (cuffed) mandatory; avoid coughing/straining at induction/emergence
  • Consider reinforced tube; secure well (head turned, drapes, long case)
• Duration: typically 3–8 hours (variable with complexity, rupture, intra-op angiography)
  • Expect prolonged immobility, fluid shifts, temperature management needs
• Pain: moderate–severe (craniotomy, temporalis muscle); multimodal analgesia while enabling neuro assessment
  • Scalp block/local infiltration + paracetamol ± low-dose opioid; avoid oversedation
• Monitoring/lines: invasive arterial line before induction if unstable/SAH; large-bore IV access; consider CVC if vasoactive infusions/poor access
  • Urinary catheter; temperature; neuromuscular monitoring; consider EEG/BIS if TIVA

Aims and key physiological principles

• Prevent aneurysm rupture/re-rupture: avoid acute surges in MAP and ICP (especially at induction, pinning, incision, emergence)
• Maintain cerebral perfusion: CPP = MAP − ICP; avoid hypotension (ischaemia) and hypertension (rupture/bleeding)
• Optimise brain conditions: relaxed brain (low-normal PaCO2, osmotherapy when indicated), avoid venous congestion (head up, neutral neck, avoid tight ETT ties)
• Enable rapid postoperative neurological assessment when appropriate (especially unruptured aneurysm or good-grade SAH)
• Prevent secondary brain injury: normoxia, normocapnia/targeted mild hypocapnia, normoglycaemia, normothermia, treat seizures, avoid anaemia

Preoperative assessment

• Ruptured vs unruptured aneurysm: ruptured = SAH physiology and complications; unruptured often elective with comorbidities (HTN, smoking)
• SAH grading and implications: WFNS/Hunt–Hess (neuro status), Fisher grade (blood load → vasospasm risk)
  • Poor grade SAH: airway protection, ventilation, ICP issues, haemodynamic instability more likely
• Complications to identify: hydrocephalus (EVD), raised ICP, rebleeding risk, vasospasm/DSCI, seizures, hyponatraemia (SIADH/CSW), cardiopulmonary dysfunction
  • SAH-related cardiac: ECG changes, troponin rise, stress cardiomyopathy, LV dysfunction; impacts induction/vasopressor choice
• Medication: nimodipine (continue), anticonvulsants if prescribed; antiplatelets/anticoagulants (more relevant to coiling but may exist)
• Baseline labs: FBC (Hb/platelets), U&E (Na+), coagulation, group & screen/crossmatch; consider ABG if ventilated/critically ill

Induction and airway

• Goals: smooth induction, avoid hypertension/tachycardia and avoid hypotension; maintain oxygenation and normocapnia
• Induction agents: propofol or thiopentone (both reduce CMRO2/CBF/ICP); consider haemodynamic reserve (SAH cardiomyopathy)
• Blunt sympathetic response: opioid (fentanyl/alfentanil/remifentanil), lidocaine, short-acting beta-blocker (esmolol), vasodilator (GTN) as needed
• Neuromuscular block: rocuronium/atracurium; avoid fasciculations and coughing/straining
• Arterial line: often placed pre-induction in SAH/unstable; otherwise immediately post-induction before pinning

Maintenance: anaesthetic technique and monitoring

• Technique: TIVA (propofol/remifentanil) or low-dose volatile + opioid; ensure immobility for microscope work and pin fixation
• Ventilation: aim PaCO2 ~4.5–5.0 kPa; brief mild hypocapnia (e.g., 4.0–4.5) for brain relaxation if needed; avoid prolonged aggressive hyperventilation (ischaemia)
• Oxygenation: avoid hypoxia; routine hyperoxia not required but ensure adequate PaO2 in SAH/vasospasm risk
• Fluids: aim euvolaemia; isotonic crystalloids (0.9% saline or balanced isotonic solutions); avoid hypo-osmolar fluids and glucose-containing solutions (unless treating hypoglycaemia)
  • Colloids generally not required; blood products if significant haemorrhage/rupture
• Blood pressure targets: individualised; avoid hypertension pre-clip; maintain adequate MAP/CPP, especially during temporary clipping and after definitive clipping
  • Have vasopressors ready (metaraminol/phenylephrine/noradrenaline) and vasodilators ready (GTN) depending on phase
• Temperature: maintain normothermia; forced-air warming, fluid warming; avoid shivering post-op (raises ICP/MAP)
• Neuro-monitoring: SSEP/MEP/EEG/processed EEG; adjust anaesthesia (TIVA, minimise volatile, avoid long-acting NMB if MEPs required)

Brain relaxation and ICP control

• Position: head up ~15–30°, neutral venous drainage, avoid neck compression; ensure ETT ties and lines not obstructing jugular venous return
• Osmotherapy: mannitol 0.25–1 g/kg or hypertonic saline (e.g., 3% or 7.5% per local protocol) when brain tight
  • Monitor serum Na+/osmolality and haemodynamics; mannitol causes diuresis and potential hypotension
• CSF drainage: via EVD or lumbar drain (selected cases); coordinate with surgeon to avoid over-drainage and herniation risk
• Hyperventilation: short-term rescue for acute brain swelling; avoid prolonged use (reduces CBF)
• Steroids: not routinely indicated for aneurysm clipping (more for tumour/vasogenic oedema); follow local practice

Key intraoperative events and how to manage them

• Mayfield pinning/scalp incision: intense sympathetic stimulus → treat with deepening anaesthesia, opioid bolus, local infiltration/scalp block, esmolol/vasodilator
• Temporary clipping: risk of ischaemia → optimise CPP, avoid hypotension/anaemia/hypocapnia extremes; discuss planned duration; consider burst suppression only if requested/centre practice
• Intraoperative rupture: call for help, inform surgeon, increase FiO2, secure large-bore access, rapid transfusion if needed, control BP (often lower MAP briefly), deepen anaesthesia, correct coagulopathy, prepare for sudden brain swelling
  • Avoid uncontrolled hypertension; avoid profound hypotension that jeopardises CPP—targets are phase- and surgeon-dependent
• Acute brain swelling: check ventilation/PaCO2, head position/venous obstruction, consider osmotherapy, CSF drainage, deepen anaesthesia; exclude surgical causes (haematoma, venous infarct)
• Seizures: treat with benzodiazepine/propofol, correct metabolic causes, consider levetiracetam/phenytoin per protocol; avoid hypoxia/hypercarbia

Emergence and postoperative care

• Plan extubation vs postoperative ventilation based on: SAH grade, intra-op events (rupture, swelling), duration, hypothermia, haemodynamic instability, airway concerns
• Smooth emergence: prevent coughing/straining (risk bleeding/raised ICP) using lidocaine, remifentanil tail, careful suctioning, antiemetics
• Analgesia: paracetamol + scalp block/local; cautious opioids (small titrated doses); consider NSAIDs only if surgeon agrees and bleeding risk acceptable
• PONV prophylaxis: high priority (vomiting increases ICP/MAP) → multimodal antiemetics
• Post-op monitoring: HDU/ICU; frequent neuro observations; BP control; manage EVD if present; watch for vasospasm/DSCI, hydrocephalus, seizures, electrolyte disturbances
  • Nimodipine continued; treat suspected vasospasm with induced hypertension/euvolemia and endovascular therapy per neurocritical care pathway

Ruptured aneurysm (SAH) specifics

• Rebleeding risk highest early; avoid hypertension and agitation; secure aneurysm early (clip/coil) where possible
• Vasospasm/DSCI typically days 3–14; anaesthetic implications: maintain CPP, avoid hypovolaemia, treat hypotension promptly, avoid excessive hyperventilation
• Hyponatraemia: SIADH vs cerebral salt wasting; treat according to volume status; avoid hypotonic fluids
• Cardiopulmonary dysfunction: neurogenic stunned myocardium, pulmonary oedema; consider echo, cautious induction, noradrenaline often preferred to support CPP

Unruptured aneurysm specifics

• Often elective: focus on comorbidities (HTN, IHD), antithrombotics, and smooth haemodynamics; aim for early wake-up and neuro exam
• Blood pressure: avoid peri-induction hypertension; avoid hypotension that risks ischaemia during temporary clipping