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Neurosurgery — Craniotomy, Aneurysm, Awake

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Specialty I · 10 min read

ICP control + smooth induction + CPP-targeted maintenance. Aneurysm rebleed and VAE are the high-stakes complications.

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Plan smooth induction for aneurysm clipping.
Maintain CPP and minimize ICP spikes.
Manage awake craniotomy.
Treat venous air embolism in sitting craniotomy.

ICP control + CPP target

CPP = MAP − ICP

Target ≥60-70 mmHg post-TBI per Brain Trauma Foundation 2017 (lowered from prior CPP 70-90 because aggressive CPP elevation worsened ARDS without neuro benefit).

Below 60 = secondary ischemic injury.

NORMAL ICP <15 mmHg; intracranial HTN ≥22 mmHg requires intervention.

TIER 1 interventions: head of bed 30° up, neutral neck (no jugular obstruction), normocapnia PaCO2 35-40 (avoid hyperventilation except as bridge), normothermia, adequate sedation, avoid PEEP >10 if possible.

TIER 2HYPERTONIC SALINE 3% 250 mL bolus OR MANNITOL 0.5-1 g/kg over 15 min (mannitol pulls free water from brain via osmosis; check serum osmolality, hold for >320 mOsm/L).

TIER 3 refractory: barbiturate coma, mild hypothermia 33-34°C, decompressive craniectomy.

Cerebral perfusion pressure: CPP = MAP - ICP (or CVP if higher); target CPP 60-70 mmHg in adults with TBI; below 50 risks ischemia, above 70 may increase ARDS.

Aneurysm clipping — smooth induction

KeyRebleed during induction is CATASTROPHIC (mortality >50%, often during laryngoscopy hypertensive spike).

SMOOTH INDUCTION protocol: pre-treat with LIDOCAINE 1.5 mg/kg + ESMOLOL 0.5-1 mg/kg + FENTANYL 3-5 mcg/kg or REMIFENTANIL 0.5-1 mcg/kg over 60 sec before laryngoscopy.

Avoid HTN spike (target SBP within 20% of baseline).

MAINTENANCEbalanced volatile + opioid OR TIVA — both acceptable.

BRAIN RELAXATION techniques

mild hypocapnia (PaCO2 30-35)
mannitol 0.5 g/kg
head elevation
optimal sevoflurane MAC <1
lumbar drain CSF removal if surgeon requests

CONTROLLED HYPOTENSION during temporary clip placement: MAP 50-60 mmHg via clevidipine or remifentanil titration; release temp clip every 3-5 min for collateral perfusion check.

Anesthetic management for craniotomy: smooth induction, avoid coughing/HTN, maintain CPP, mild hyperventilation (PaCO2 30-35) only briefly, mannitol/hypertonic saline for ICP, avoid N2O with pneumocephalus.

Preoxygenation: replace nitrogen with oxygen to extend safe apnea time; 100% O2 for 3-5 min OR 8 vital capacity breaths in 60 sec; target end-tidal O2 >=90% prior to induction. — Anesthetic management for craniotomy: smooth induction, avoid coughing/HTN, maintain CPP, mild hyperventilation (PaCO2 30-35) only briefly, mannitol/hypertonic saline for ICP, avoid N2O with pneumocephalus.

Sudden bleeding readiness

KeyType + crossmatch 4 units; some institutions 6 units for high-risk aneurysm.

Two large-bore IVs + arterial line + central access (CVL for vasopressor administration + CVP).

Cell saver setup if long case anticipated.

MTP activation criteria pre-discussed.

VASOPRESSORS drawn + ready: norepinephrine first-line, phenylephrine 100 mcg syringe, epinephrine 10 mcg syringe + 1 mg ampule for severe instability.

MANNITOL 100 g + hypertonic saline 3% on standby.

Open communication with surgeon about bleeding tolerance + temp clip + endovascular rescue (interventional neuroradiology paged).

Discuss the disaster plan in pre-incision time-out.

Awake craniotomy

Indicationeloquent-cortex tumors (motor strip, language, sensory) — intraoperative cortical mapping enables surgeon to maximize tumor resection while preserving function.

TECHNIQUESASLEEP-AWAKE-ASLEEP (full GA + LMA for opening, wake during mapping, re-induce + LMA for closing) OR MAC throughout with regional/scalp block.

SEDATIONdexmedetomidine 0.5-1 mcg/kg/hr + remifentanil 0.05-0.1 mcg/kg/min titrated to comfortable + cooperative; minimize benzo (impairs cooperation).

SCALP BLOCK with 0.25-0.5% bupivacaine + epinephrine: 6 nerves bilateral — supraorbital, supratrochlear, zygomaticotemporal, auriculotemporal, lesser + greater occipital.

PATIENT SELECTION + cooperation critical (psychological eval, claustrophobia screen).

RISKS

seizure during stimulation (cold saline irrigation aborts)
airway loss in awake phase
agitation
vomiting
conversion to GA

Cranial nerves I-XII anesthesia-relevant function: airway-related (V trigeminal sensory, IX glossopharyngeal, X vagus, XII hypoglossal), eye (II, III, IV, VI), and reflexes for awake fiberoptic intubation.

VAE in sitting craniotomy

KeySitting / semi-sitting position used for posterior fossa surgery + cervical spine — open dural sinuses or dura mater BELOW heart level entrain air.

INCIDENCE 25-50% in sitting position; clinically significant in 5-10%.

DETECTION (in order of sensitivity): precordial Doppler (most sensitive — characteristic 'mill-wheel' or 'machinery' murmur audible), TEE (gold standard, detects bubbles in cardiac chambers), sudden ETCO2 DROP (gas embolism replaces effective gas exchange), unexplained hypotension, hypoxia, sustained tachycardia.

TREATMENT

STOP air entry (flood surgical field with saline, surgeon compresses jugulars)
Trendelenburg or LEFT LATERAL position (traps air in RV apex away from RVOT)
aspirate air via CVP catheter (Durant maneuver — multi-orifice CVL pre-placed for this)
100% O2 (denitrogenates remaining air bubbles)
supportive vasopressors

Pre-op CVL with multi-orifice catheter often placed for aspiration capability in sitting cases.

Venous air embolism (VAE): high risk in sitting craniotomy, posterior fossa, C-section, laparoscopy. Detection by precordial Doppler (most sensitive non-invasive), sudden drop in ETCO2, mill-wheel murmur. Manage: flood field, left-lateral Durant position, aspirate central line, 100% O2.

Posterior fossa + brainstem surgery

KeyBrainstem manipulation sudden BRADYCARDIA, asystole, hypertensive crisis (Cushing reflex), or arrhythmia — sentinel for cardiovascular center compression.

Treat

surgeon stops manipulation

usually self-resolves within seconds

persistent atropine, escalate

ETT MIGRATION with neck flexion in prone/sitting (carina rises during flexion, ETT may bronchial-intubate) — re-check tube depth after positioning.

Tongue + facial edema from prolonged prone with shoulder roll — limit duration, free face airspace.

Eye injury risk: corneal abrasion + ION + direct globe pressure meticulous eye taping + protection + frequent position checks.

POST-OP CAREICU admission standard for posterior fossa cases; monitor for apnea + cranial nerve dysfunction + hemorrhage.

Complications of the sitting position: VAE, hemodynamic instability, pneumocephalus, peripheral nerve injury, macroglossia; risks balanced by improved surgical access for posterior fossa and cervical spine.

MEP/SSEP-friendly anesthetic

KeySpine + intracranial cases with neurophysiologic monitoring require anesthetic that doesn't suppress signals.

MEPs (motor evoked potentials): suppressed by VOLATILE >0.5 MAC and by all NMBs after the intubating dose wears off.

STANDARD MEP-FRIENDLY

TIVA propofol 100-150 mcg/kg/min + remifentanil 0.1-0.3 mcg/kg/min + low-dose ketamine 0.15 mg/kg/hr

no maintenance NMB (allow intubating roc to wear off; if blockade needed for surgery let surgeon know)

SSEPs more forgiving — tolerate 0.5-0.7 MAC volatile.

BAEPs most resistant.

EEG and processed EEG (BIS) work with most agents.

Total intravenous anesthesia (TIVA): indications (MH risk, neuromonitoring, ENT/laser airway), common agents (propofol 100-200 mcg/kg/min, remifentanil 0.05-0.5 mcg/kg/min), and monitoring with BIS/processed EEG.

Carotid endarterectomy + stroke prevention

KeyDiscussed in vascular surgery lecture — relevant here because of cerebral perfusion implications.

Maintain MAP at or slightly above patient's awake baseline during cross-clamp (preserve collateral perfusion via Circle of Willis).

NIRS (cerebral oximetry) useful adjunct during GA — 20%+ drop in rSO2 from baseline during clamp suggests inadequate collateral, may need shunt.

Post-CEA hyperperfusion syndrome — strict BP control postop SBP <140.

New focal neuro deficit post-CEA emergent re-exploration or imaging.

Advanced neuromonitoring overview: TEE, NIRS regional cerebral oximetry, SSEPs during spine surgery, EEG during carotid endarterectomy for ischemia detection.

⚠ Common pitfalls

Allowing hypertension at clipping — rebleed risk; pre-treat with esmolol + opioid.
Excessive PaCO₂ swing — sudden hyperventilation can rupture aneurysm via wall tension shift.
Sitting craniotomy without precordial Doppler — VAE undetected.
Postop hyperventilation as routine — drops CBF, harms outcome.

💎 Clinical pearls

CPP 60-70 target; transmural pressure (MAP − ICP) is what matters for the aneurysm wall.
Awake craniotomy: dex + scalp block + scalp infiltration; asleep-awake-asleep for cortical mapping.
VAE management: jugular compression, head-down, aspirate from CVC, 100% O₂, supportive.
Mannitol 0.25-1 g/kg 30 min before dural opening — surgical brain relaxation.

Recap

CPP 60-70 target; transmural pressure (MAP − ICP) is what matters for the aneurysm wall.
Awake craniotomy: dex + scalp block + scalp infiltration; asleep-awake-asleep for cortical mapping.
VAE management: jugular compression, head-down, aspirate from CVC, 100% O₂, supportive.
Mannitol 0.25-1 g/kg 30 min before dural opening — surgical brain relaxation.

Mark each section done to complete the module.