Abstracts

RATIONALE: Routine hyperventilation (HV) in our department consists of deep breathing for 3 minutes once during the EEG. An exception to this is absence patients, who are asked to HV for 4 minutes on 2 occasions. The aim of this study was to determine if it is necessary to treat suspected absence patients differently and have them hyperventilate for the extra minute or the second HV.
METHODS: The study involved looking at the EEG of 23 neurologically normal, untreated patients who had at least one absence seizure recorded during their EEG. We looked at when in HV their seizures occurred. We also noted if they had any seizures outside of HV.
RESULTS: Twenty-one of the 23 patients had HV induced seizures. Twenty of these had at least one seizure in the first HV. Of these twenty, 19 had seizures within the first 3 minutes of HV. Thirteen patients had seizures in the second HV. Only one patient had a seizure exclusively in the second HV. This patient had his only HV induced seizure in the fourth minute of the second HV. Twenty-one patients had seizures in their resting EEG.
Of the 23 untreated children with recorded absences in their EEG, only two patients did not have seizures in their resting EEG. Both of these had seizures recorded within the first 3 minutes of the first HV. Of the patients with HV induced seizures, 2 had them exclusively in the 4th minute of HV. One of these was the only patient to have HV induced seizures exclusively in the second HV. Both of these patients had the majority of their seizures out side of HV. Seizures in the resting EEG were very frequent in this group of untreated patients. Had we followed our standard protocol of a single 3 minute HV, the diagnosis of seizures would not have been missed in any patient.
CONCLUSIONS: It is not necessary to hyperventilate untreated patients suspected of having absence seizures for four minutes on two occasions. In our experience a single 3 minute HV would suffice.