A thorough preanesthetic examination should be performed to establish the likely cause of seizures .
Antiepileptic therapy should not be discontinued perioperatively.
Epilepticogenic drugs should be avoided in the anesthetic protocol.
Preanesthetic examination
Differentiate seizure activity from syncopal attacks (cardiac/respiratory disease) or muscle fatigue (neuromuscular dysfunction).
Rule out extracranial causes of seizures (hypoglycemia , hypocalcemia , electrolyte abnormalities, neuromuscular disease, cardiac disease, respiratory disease, hepatic/renal dysfunction,) using full hematology and biochemistry in conjunction with clinical examination.
The aim of premedication is to minimize stress prior to and during induction and during recovery, whilst also providing analgesia .
According to the manufacturers of acepromazine , the drug should not be used in epileptic patients since high dose phenothiazines have been reported to reduce seizure threshold. Acepromazine has been used at clinically relevant doses (8-59 µg/kg) in epileptic patients and did not appear to alter the incidence of perioperative seizures from those not receiving the drug (Garner J L et al2004).
Opioids do not alter seizure activity and can be used to provide analgesia and sedation.
Alpha-adrenoceptor agonists, even at low doses such as medetomidine 1-2 µg/kg, can provide good sedation, especially in conjunction with opioids. These agents should be used with caution in patients with suspected intracranial disease since the alterations in blood pressure may alter cerebral perfusion.
Benzodiazepines can cause dysphoria in patients that are not actively seizuring and so should be reserved for use as co-induction agents.
Induction of anesthesia
Propofol and thiobarbiturates can both be used for induction of anesthesia .
Ketamine should not be used as seizure-type activity manifested as hypertonia and muscle tremors have been reported in recovery.
Hypoxemia should be avoided during induction of anesthesia.
Maintenance of anesthesia
Enflurane is contraindicated due to epileptiform changes in the EEG and seizure activity in recovery.
Sevoflurane and isoflurane have less detrimental effects on cerebral blood flow and metabolism coupling than halothane .
Nitrous oxide increases cerebral metabolic demand is best avoided.
Total intravenous anesthesia with propofol is suitable for maintenance of anesthesia and is commonly used for long term control of status epilepticus .
Mask induction can lead to excitement and is therefore best avoided.
Sevoflurane is emerging as the anesthetic maintenance agent of choice for neuroanesthesia in humans.
Intravenous crystalloids should be administered.
Recovery period
Constant observation of the patient is required, preferably by someone who is able to administer antiepileptic medication as required.
Stimulation should be avoided by providing a quiet environment and good analgesia.
Fluid administration should be continued perioperatively until the patient is able to eat and drink.
Control of prolonged seizure activity (status epilepticus or cluster seizures) is necessary to prevent further neurological damage and minimize hypoxemia , hypoglycemia , and hyperthermia .
A clear airway should be established and flow-by oxygen administered.
Baseline hematology and biochemistry, including electrolytes, should be taken once seizure activity has been controlled and blood glucose levels checked and corrected if necessary.
Intravenous access should be secured.
A thorough history including any systemic disease or exposure to potential toxins should be taken.
Temperature should be taken and the patient slowly cooled if hyperthermia (>40ºC) is present.
Control seizure activity
Initially diazepam 0.2-2 mg/kg IV or per rectum or midazolam 0.05-0.25 mg/kg IV or IM. This therapy can be repeated 2-3 times whilst loading with other antiepileptic agents is achieved.
Phenobarbitone loading 2-4 mg/kg IV or IM repeated every hour for three hours (maximum 24 hour does 24 mg/kg)
Management of refractory seizures
If not responding to the above therapeutic protocol, more aggressive treatment is required.
Propofol 4-mg/kg IV for initial control followed by sedation with a constant rate infusion 0.1-0.4 mg/kg/minute. Good airway control and respiratory monitoring is required.
Low doses of pentobarbital should be administered to effect (2-15 mg/kg IV) and infusions can be administered at 0.1-0.2 mg/kg/minute.
The above agents should be withdrawn slowly by tapering the dose to effect.
Sevoflurane or isoflurane may be administered for prolonged control of seizures however may cause hypotension and require endotracheal intubation.
Loading with potassium bromide (100 mg/kg every 4 hours for 24 hours) may also be considered.
Supportive care
Heavily sedated or anesthetized animals require a high level of observational and supportive care.
A patent airway should be established.
Monitoring should include pulse oximeter (if breathing room air) and blood pressure monitoring .
Adequate bedding should be provided and the patient should be turned at least every four hours.
If intubated, oral hygiene should be addressed and the mouth moistened.
Eyes should be lubricated every 6 hours.
Placement of an indwelling urinary catheter should be considered to minimize soiling and discomfort for the patient.
Anesthesia may be necessary in epileptic patients for surgery or diagnostic procedures not linked to the condition or else for specific management of cluster seizures or status epilepticus. Antiepileptic drug therapy should not be discontinued prior to anesthesia whilst epilepticogenic drugs should be avoided.
Garner J L, Kirby R, Rudloff E (2004) The use of acepromazine in dogs with a history of seizures.Abstract at the 10th International Veterinary Emergency and Critical Care Symposium, California.
Vetstream contributor(s)
J C Brearley MA VetMB PhD DVA DipECVA MRCA MRCVS, The Queen's Veterinary School Hospital, University of Cambridge, Madingley Road, Cambridge, CB3 0ES, UK.
E A Leece BVSc CVA DipECVA MRCVS, Animal Health Trust, Lanwades Park, Newmarket, Suffolk, CB8 7UU, UK.
