Will a critical level of hyperventilation-induced hypocapnia always induce an absence seizure?

Area of Science:

• Pediatric Neurology
• Epilepsy Research
• Respiratory Physiology

Background:

• Absence epilepsy is a common epilepsy syndrome in children.
• Hyperventilation is a known trigger for absence seizures.
• The physiological mechanisms linking hypocapnia to seizure provocation require further elucidation.

Purpose of the Study:

• To investigate the correlation between the degree of hypocapnia and absence seizure frequency.
• To identify a critical PCO2 threshold for reliable absence seizure provocation.
• To assess the impact of supplemental CO2 and O2 on seizure activity.

Main Methods:

• Twelve untreated children with newly diagnosed absence epilepsy underwent continuous EEG and end-expiratory CO2 monitoring.
• Recordings were performed during quiet respiration and hyperventilation using four gas mixtures (room air, 100% O2, 4% CO2, 4% CO2 + 96% O2).
• Hyperventilation continued until absence seizure onset or exhaustion.

Main Results:

• Supplemental CO2 breathing reduced spike and wave bursts and total spike and wave duration during quiet respiration (p < 0.05).
• Supplemental O2 had no significant effect on seizure activity.
• In 67% of subjects, absence seizures were reliably provoked by hypocapnia, with critical PCO2 levels ranging from 19 to 28 mmHg; however, three children did not have seizures, and one had inconsistent provocation.

Conclusions:

• Hypocapnia reliably provokes absence seizures in a majority of children with absence epilepsy.
• A critical PCO2 threshold for seizure provocation exists but varies individually.
• Further research is needed to determine if hypocapnia sensitivity predicts antiepileptic drug response or seizure remission.