Anesthesia for Epilepsy Surgery

simpsons_seizure

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
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