FRCA Notes

Epilepsy

Resources

  • Epilepsy is a clinical condition characterised by a tendency to have seizures
  • Seizures are paroxysmal, episodic, abnormal, spontaneous discharges of electrical activity in the brain

  • Thought to arise as a general imbalance of inhibitory and excitatory neurotransmitters
    • GABA is the main inhibitory neurotransmitter (present at 30% of synapses)
    • Glutamate is the main excitatory neurotransmitter
Aetiology of epilepsy
Idiopathic (65%)
Vascular (10%)
Congenital (8%)
Trauma (6%)
Neoplastic (4%)
Degenerative (4%)
Infection (3%)

Generalised seizures

  • The whole cerebral cortex is involved and consciousness is impaired
  • Types include:
    • Tonic-clonic
    • Tonic
    • Myoclonic
    • Absence
    • Atonic/akinetic

Partial seizures

  • One region of the cortex is impaired (typically temporal lobe)
  • Symptoms depend on area of the brain affected
  • There may be secondary generalisation to a generalised seizure

  • Partial seizures may be further sub-classified according to whether they are:
    • Simple - in which consciousness is preserved and patients may have a memory of the event
    • Complex - in which consciousness is impaired and patients have no memory of the event

Perioperative management of the patient with epilepsy


History and examination

  • History of epilepsy e.g. frequency of seizures, nature of seizures
  • Underlying pathology/aetiology of seizures if not idiopathic
  • Occupation and driving status

  • Drug history
    • Efficacy of control
    • Side-effects from AED

  • MDT input from Neurologists if significant concern

Investigations

  • FBC, LFT and clotting should be done on patients taking carbamazepine and valproate
  • U&E as dysnatraemias are common
  • ECG if on sodium channel antagonist as may cause Brugada-type ST changes & J-wave abnormalities
  • Consider optimising plasma AED levels

  • Consider CXR to check vagal nerve stimulator position (if present)
    • These pulse generators/stimulators are sometimes used in drug-refractory epilepsy, particularly partial epilepsy
    • They send regular stimuli to the vagus nerve
    • They are not effective immediately and rarely prevent seizures entirely
    • Battery lasts 5 - 10yrs

  • It's important patients receive AED's in a timely manner
    • In general, AED's have long half-lives so one missed or delayed dose is well tolerated
    • Some agents are only available orally, so if NBM need an alternative route of administration
    • Liaise with Neurology and Pharmacy

  • Standard monitoring and access

Regional anaesthesia

  • The benefits of regional anaesthesia must be considered against the risk of intra-operative seizure in an awake patient
  • Anxiety-induced hypocapnoea may alter seizure threshold

Induction

  • Propofol or thiopentone induction
  • In general avoid ketamine or etomidate that may lower seizure threshold

  • Some AED's are enzyme inducers e.g. phenytoin, carbamazepine so increased doses of anaesthetic agents and NMBA may be required
  • If NMBA are used then a peripheral nerve stimulator should be used

Maintenance

  • AED-related hepatic enzyme induction may cause increased metabolism of halogenated volatile agents and increase risk of halothane hepatitis
  • There may be greater opioid metabolism, leading to increased analgesic requirements
    • Some suggestion to avoid alfentanil as it is potentially epileptogenic
  • Avoid hypoxia and hypercapnia throughout the case as these can lower seizure threshold
  • If on ketogenic diet, use normal saline instead of lactate-containing balanced crystalloids
EEG activation EEG suppression
Low-dose propofol Clinical doses of propofol
Ketamine Thiopentone
Etomidate Isoflurane
Sevoflurane, enflurane Desflurane
High-dose fentanyl (15 - 35μg/kg) Low-dose fentanyl (<5μg/kg)
Alfentanil
High-dose morphine


  • Avoid tramadol, alfentanil and pethidine as these are associated with a lowering of the seizure threshold
  • Caution with certain antibiotics that may also lower seizure threshold; penicillins, carbapenems, fluoroquinolones and cephalosporins
  • Restart AED as soon as possible

Pseudo-seizures

  • Volatile agents can cause shivering and shaking
  • Hypothermia can cause shivering
  • Some agents may cause dystonic reactions
  • Pseudo-seizures relating to psychosomatic illness can occur