Anesthesia for Epilepsy Surgery

Background and Pathophys

• 0.5% to 1% of general pop
• recurrent seizure activity
• 30% of patients have no relief from meds –> surgery
• Altered regulation of electric activity, symptom of underlying process/disease
  • interictal spikes on eeg
  • impaired GABA inhibition, altered neurotransmitters
• Generalized = both hemispheres, get LOC; Partial  = one area of brain, no impair consc.; Complex partial = one area then spreads and lose consc., most common, includes temporal lobe epilepsy

Surgery for patients with severe medication related side effects, TLE is most response to surgery

Pre-Op Assessment

• Get drug levels, assess for side effects from meds (see table)
• c/w anti-epileptics periop, giving benzos is acceptable most times but check with surgeon for plan

I/O

• communicate to surgeon regarding recording cerebral activity, activating epileptic focus and cortical mapping
• Electorcorticography (ECoG) = grid electrode over cortex, map foci of epilepsy
  • GA with techniques to minimize effect on ecog

Anesthesia effects on Electrophysiology of Brain

• Dose related! in general, low dose = proconvulsant, high dose = anticonvulsant
• Thiopental is anticonvulsant
• Methohexital and Etomidate = proconvulsant; used to activate foci
• Propofol
  • activate EEG in temporal lobe epilepsy
  • can produce seizures and opisthotonos in non-epileptic patients
  • dose dependent ==> activates EEG in low dose, burst suppression (anticonvulsant) in higher clincal dose
• Diazepam / Benzos : anticonvulsant
• Inhalationals: low-dose iso is best, isoelectric at 2 MAC, sevo and des similiar
  • high dose enflurane + elevated paCO2 =  seizures!
• Nitrous: dose dependent changes in EEG, high % = anti-convulsant

Typical Plan:

• GA + surgical needs, consider similar to craniotomy
• Volatile + short opioid good choice to minimize epileptic activity
• prop + remi not studied well on ECoG
• Scalp block + opioid/N2O + precedex
• To provoke a seizure for surgery use small dose:
  • methohexital
  • thiopental
  • propofol
  • alfentanil

I/O seizures that are not provoked on purpose –> look for HTN, Tachy, increased ETCO2

• deepen and bolus prop

Be a bloke, don’t provoke:

• avoid aforementioned proconvusl drugs
• light anesth and hypoxemia is bad, co2 normal range
• Metabolic: low sugarl, calcium or Mag, any out of whack Na, uremia
• Hematomas and hx of poor controlled epilepsy (duh)

P/O:

• Neurosurg ICU to monitor for and minimize risk of p/o seizures