Introduction #
Idiopathic epilepsy is a common neurologic disorder in dogs and is less frequently diagnosed in cats. Feline seizures often stem from identifiable intracranial or metabolic causes, but true idiopathic epilepsy does occur. Anesthetic management of dogs and cats with idiopathic seizures demands careful planning to minimize seizure risk and ensure smooth induction, maintenance, and recovery. Understanding how anesthetic agents affect seizure threshold and central nervous system physiology is critical. This essay discusses anesthetic drug protocols, contraindicated agents, and perioperative management strategies for dogs and cats with idiopathic epilepsy, framed for expert veterinary anesthetists.
Preanesthetic Assessment and Stabilization #
A thorough preanesthetic evaluation is essential. Elective procedures should be delayed until the patient is seizure-free for a minimum period (typically a few weeks). Recent seizure frequency, severity, known triggers, and time of last episode must be recorded. Hospitalization should be streamlined to reduce stress, with early premedication and quiet environments provided.
Routine bloodwork should be reviewed for abnormalities that might lower the seizure threshold, including hypoglycemia, electrolyte imbalances, and hepatic dysfunction. In cats, metabolic and structural causes must be ruled out given their lower incidence of idiopathic epilepsy.
Chronic anticonvulsant therapy must be continued perioperatively. Owners should administer morning doses of phenobarbital, levetiracetam, zonisamide, or potassium bromide. For agents causing GI upset when fasted, a small food amount is acceptable. In emergencies, rectal or IV routes may be used to maintain therapeutic levels. Emergency seizure medications (e.g., diazepam, midazolam, injectable phenobarbital or levetiracetam) should be prepared in advance, and a response plan should be outlined.
Anesthetic Drug Selection and Protocols #
Drug selection for epileptic patients should avoid agents that reduce seizure threshold and instead favor drugs with anticonvulsant properties. A balanced anesthetic protocol involving appropriate premedication, a smooth induction, and careful maintenance is ideal.
Sedation and Premedication #
Benzodiazepines such as midazolam or diazepam are sometimes preferred for their anxiolytic and anticonvulsant effects. They can be combined with opioids (methadone, hydromorphone, or butorphanol) for sedation and analgesia. In cats, benzodiazepines may cause paradoxical excitement but are generally safe when used IV or with other agents.
Opioids are safe and beneficial for their analgesic properties. Phenothiazines, particularly acepromazine, were historically avoided due to concerns about seizure risk, but current evidence supports the safety of low doses. Alpha-2 agonists like dexmedetomidine offer effective sedation and analgesia and are not contraindicated if used judiciously, though care must be taken with cardiovascular effects.
Induction of Anesthesia #
Preferred induction agents include propofol and alfaxalone, both of which possess anticonvulsant properties and provide smooth induction. Propofol is especially favored due to its neuroprotective effects. Thiopental is another option where available, although less common today.
Etomidate may be considered in patients with cardiac compromise; however, its tendency to cause myoclonus requires co-administration with a benzodiazepine. Dissociatives, especially ketamine and tiletamine (Telazol), usually are routinely used as they increase cerebral metabolic rate and have been associated historically with seizures in susceptible patients.
Maintenance of Anesthesia #
Maintenance is typically achieved with inhalants such as isoflurane or sevoflurane. These agents are considered safe, with minimal evidence of proconvulsant activity at clinical concentrations. Nonetheless, minimizing the inhalant concentration by using balanced techniques is advised.
Balanced anesthesia may incorporate opioid constant rate infusions (CRIs), intermittent boluses of propofol, or even total intravenous anesthesia (TIVA) using propofol and fentanyl. Regional techniques like nerve blocks and epidurals are excellent adjuncts for multimodal analgesia, reducing the need for systemic agents.
Neuromuscular blockers, when used, require vigilant monitoring since seizure activity may be masked. Most procedures in epileptic animals do not require them.
Contraindicated and High-Risk Agents #
Certain drugs and practices should be avoided or used with extreme caution in seizure-prone patients:
- Dissociatives: Ketamine and tiletamine are often avoided due to CNS excitatory effects.
- High-dose phenothiazines: While low-dose acepromazine is acceptable, high doses are avoided due to theoretical risks.
- Flumazenil: Reversal of benzodiazepines can precipitate rebound seizures and should be reserved for emergencies.
- Hypocapnia and hypercapnia: Extremes in CO₂ levels affect cerebral blood flow and seizure threshold; normocapnia is ideal.
- Light planes of anesthesia: Inadequate depth can precipitate seizures; maintain consistent and appropriate anesthetic depth.
Perioperative Management and Monitoring #
Maintaining hemodynamic and neurologic stability is critical. Avoid hypotension to preserve cerebral perfusion pressure. Monitor mean arterial pressure and support circulation with fluids or vasopressors if necessary.
Ventilation should aim for normocapnia (ETCO₂ 35–45 mmHg). Hypercapnia can increase intracranial pressure, while excessive hyperventilation risks cerebral ischemia.
Temperature regulation is important. Both hyperthermia and hypothermia can affect neuronal stability. Maintain normothermia throughout the anesthetic event.
Recovery should occur in a quiet, dimly lit space. Minimize visual and auditory stimulation. A smooth, controlled emergence is critical.
Postoperative Care and Recovery #
Postoperative vigilance is essential. Analgesia should be continued with opioids and adjuncts, ensuring pain is controlled without CNS excitation. NSAIDs may be added if appropriate.
Resuming oral anticonvulsants promptly is crucial. If the patient is not alert enough to swallow, alternative administration routes (IV or rectal) must be used.
Monitor closely for signs of seizure activity. Be prepared to intervene with midazolam or diazepam if needed. Some patients may benefit from overnight observation. Clear communication with the owner regarding at-home monitoring, medication schedules, and seizure response protocols is vital.
Often animals on anticonvulsant medications will have decreased anesthetic requirements and/or longer recovery times.
Conclusion #
Anesthesia in dogs and cats with idiopathic epilepsy requires a thoughtful, tailored approach. With proper drug selection, continuation of anticonvulsant therapy, and careful perioperative management, these patients can safely undergo anesthesia for surgical and diagnostic procedures. Propofol, benzodiazepines, and opioids form the backbone of most protocols, while dissociatives and certain adjuncts are best avoided. The key lies in preparation, vigilance, and a commitment to minimizing stress and seizure risk throughout the anesthetic continuum.
