Which inhalational anesthetic agents are known to prolong seizure duration or lower the seizure threshold in patients with epilepsy?

Which Anesthetic Increases Seizure Duration in ECT

Ketamine is the anesthetic agent that increases seizure duration during electroconvulsive therapy (ECT), and is listed as an acceptable alternative to methohexital for this purpose. 1

Anesthetic Agents for ECT

Standard and Alternative Agents

The standard anesthetic protocol for ECT includes:

• Methohexital - the most commonly used anesthetic agent 1
• Acceptable alternatives that may prolong seizure duration include:
  • Ketamine - specifically noted as an alternative with sympathomimetic effects 1
  • Etomidate 1
  • Thiopental sodium 1

Seizure Duration Considerations

Adolescents typically have lower seizure thresholds and may experience more prolonged seizures with ECT compared to adults, making careful monitoring essential. 1 The target seizure duration should be 30-90 seconds as measured by EEG. 1

Agents That Decrease Seizure Duration

Several medications can shorten seizure duration or increase seizure threshold, which is undesirable in ECT:

• Benzodiazepines (midazolam, lorazepam, diazepam) - may increase seizure threshold and are used to terminate prolonged seizures 1
• Carbamazepine - has been reported to cause failure to induce seizures 1
• Propofol - has reliable anticonvulsant effects 2

Agents That May Prolong Seizures

When seizure induction is inadequate, consider:

• Caffeine augmentation - intravenous caffeine given 2-3 minutes before ECT can lengthen seizure duration, though this has only been studied in adults and may cause untoward side effects 1
• Theophylline - known to prolong seizure duration at both therapeutic and toxic levels 1

Clinical Pitfalls

Avoid concurrent use of medications that lower seizure threshold during ECT, including:

• Trazodone (associated with prolonged seizures) 1
• Lithium (reports of acute brain syndrome) 1

Prolonged seizures (>180 seconds) should be terminated with additional methohexital, diazepam, or lorazepam to prevent hypoxia-related complications. 1