5% CO₂ inhalation suppresses hyperventilation-induced absence seizures in children.

Hyperventilation can cause respiratory alkalosis by exhaling CO2, and is often used to confirm diagnosis of absence epilepsy. CO2 has long been known for its anticonvulsant properties since the 1920s. In this pilot study, we aimed to determine whether inhaling medical carbogen containing 5% CO2 and 95% O2 can suppress hyperventilation-induced absence seizures and spike-and-wave discharges (SWDs). We examined 12 patients whose absence seizures were induced by hyperventilation using video electroencephalographic recording for at least 4h. The patients were asked to hyperventilate for 3 min while breathing the following gases: (1) room air (12 patients); (2) carbogen (12 patients); and (3) 100% O2 (8 patients). Eight out of twelve patients were also examined in room air through pretreatment with carbogen for 3 min before the 3 min hyperventilation. Compared with hyperventilation in room air, hyperventilation supplemented with 5% CO2 had the following effects: (a) decrease in the number and duration of seizures; (b) prolonged appearance of epileptic discharges; and (c) reduction in the number and duration of SWDs (P<0.001). However, pretreatment with 5% CO2 and 100% O2 supplement did not yield similar effects. We demonstrated that 5% CO2 could suppress hyperventilation-induced absence seizures and SWDs, supporting the claim that 5% CO2 is an effective anticonvulsant agent. Our pilot study provides clinical basis that 5% CO2 inhalation could be a therapeutic approach for hyperventilation-related seizures.