34. Epilepsy Flashcards
You are asked to anaesthetise a 50-year-old male for an elective open
cholecystectomy. On your pre-operative visit, you discover he is a
known epileptic.
Tell me about epilepsy?
Epilepsy is defined as two or more unprovoked epileptic seizures. The quoted
incidence of active epilepsy in the community varies but in the US it is quoted
as 0.8% (8 per 1000). Approximately 9% of people will have at least one
seizure in their lifetime and 3% will be given the diagnosis of epilepsy at some
point. Males have a greater incidence of epilepsy than females
Do you know any classification syndromes for epilepsy? Has this
changed recently
Description of epilepsy is based on five parts or ‘axes’:
- Ictal phenomenology.
- Seizure type, e.g. self-limiting or continuous, generalised or focal.
- Syndrome. Diagnosis of known epilepsy syndromes if possible.
- Aetiology (if known).
- Impairment.
What side effects are associated with anti-epileptic drugs
Common side effects to most of these drugs include sedation, somnolence, fatigue and weight changes. There are more specific blood dyscrasias and abnormalities associated with certain agents.
Blood abnormality Drugs
Hyponatraemia
Carbamazepine
Abnormal LFTs
Carbamazepine
Sodium valproate
Anaemia
Phenytoin
Phenobarbitone
Thrombocytopaenia
Carbamazepine
Sodium valproate
Leukopaenia Carbamazepine
What are the implications of anaesthetic drugs in this patient?
IV agents
Pro-convulsant and anti-convulsant properties of anaesthetic agents
Many agents have both pro and anti-convulsant properties.
Intravenous induction agents may cause excitatory phenomena, while also having anti-convulsant properties
tomidate may produce EEG changes and
prolong the seizure duration during ECT compared to propofol
Propofol may cause
excitatory movements, but is thought to be safe in epilepsy
Thiopentone is a potent anti-convulsant despite
excitatory phenomena at induction.
Other agents include ketamine, which may cause excitatory phenomena,
but produces EEG suppression and has been used to treat status epilepticus,
and benzodiazepines have clear anti-convulsant properties.
Volatiles
NMB
Regarding volatile agents, seizures have been reported following enflurane
and EEG changes may be seen many hours after administration.
Neuromuscular blocking drugs have theoretical implications as the
breakdown product of atracurium, laudanosine, is pro-convulsant in high
concentrations in dogs, but does not appear to be a clinical problem in
humans.
Interaction between anaesthetic agents and anti-epileptic medication
Many of the anti-epileptic medications have a sedative action on patients.
Some of the drugs cause
enzyme induction (phenytoin, carbamazepine,
primidone, and barbiturates),
while others may cause enzyme inhibition
How would you anaesthetise this patient?
The key consideration is the limitation of seizure activity in the peri-operative period.
Pre-operative:
Ensure epilepsy is well controlled pre-operatively (if not, then
referral to a neurologist may be appropriate) and that anti-epileptic
medication is continued peri-operatively.
This may involve changing from oral to parenteral preparation to ensure the patient does not miss a dose of their medication.
Urea and electrolyte levels should be measured and
corrected.
Full blood count is indicated if haemopoetic side effects of
medications are possible.
Some anaesthetists would advocate
benzodiazepine pre-medication for this patient.
Induction:
Induction: Full anaesthetic monitoring and pre-oxygenation.
Intravenous
induction with opioid (fentanyl), induction agent (thiopentone would seem
most appropriate), and neuromuscular blockade (atracurium), followed by
endotracheal intubation and ventilation
Maintenance:
Volatile agent maintenance (not enflurane) in oxygen and air
with positive pressure ventilation ensuring normocapnoea. Close
observation for signs of seizure activity (movement, pupil changes,
autonomic activity). This should be managed with intravenous
benzodiazepines as first line and with intravenous sodium valproate or
phenytoin as second line. Systemic opioids such as morphine are suitable for
analgesia. Normothermia and normoglycaemia should be maintained.
Emergence
Emergence: Reversal of neuromuscular blockade and ‘awake’ extubation
should be performed. Delay in emergence may be due to unidentified
seizures or interactions of anti-epileptic medication and anaesthetics
Post-operative:
Post-operative: Early re-introduction of anti-epileptic medication. Sodium
valproate and phenytoin are available as intravenous preparations if the
enteral route is unavailable. Patients with recurrent post-operative seizures
are best nursed on a high dependency unit. A patient-controlled morphine
infusion is suitable for post-operative pain relief if the patient is able to
comply.
