Relationship between Hyperventilation-Induced Electroencephalographic Changes and PCO(2) Level

BACKGROUND AND PURPOSE: We conducted this study to define the relationship between the hyperventilation-induced EEG changes (HV-EEG changes) and PCO(2) METHODS: In consecutive EEG recordings of 190 patients, we gathered data on PCO(2) during the hyperventilation procedure. The data included baseline PCO(2) (B-PCO(2)), PCO(2) after 5 min of hyperventilation (5 min-PCO(2)), the mean value of the PCO(2) (M-PCO(2)), and the difference between B-PCO(2) and 5 min-PCO(2) (ΔPCO(2)). We divided the enrolled patients into two groups by hyperventilation response (response group and no-response group), presence of epilepsy (epileptic group and non-epileptic group) and age (child-adolescent group and adult group) repeatedly. We compared the four variables between the two groups in each pair. RESULTS: ΔPCO(2) was 14.2±5.0 mmHg (mean±SD) in response group (n=48) and 12.4±5.0 in no-response group (n=142; p=0.033) for all the patients. For adult patients only, 5 min-PCO(2) was 24.3±3.4 in response group (n=30) and 26.2±4.6 in no-response group (n=115; p=0.048), and ΔPCO(2) was 15.8±4.0 and 12.9±5.0, respectively (p=0.004). In non-epileptic patients, 5min-PCO(2) was 23.4±2.2 in response group (n=7) and 26.3±3.8 in no-response group (n=44; p=0.026), and ΔPCO(2) was 15.9±4.3 and 12.7±3.9, respectively (p=0.053). CONCLUSIONS: In adults and non-epileptic patients, ΔPCO(2) and 5 min-PCO(2) may be crucial to the induction of EEG changes by hyperventilation. PCO(2) could be a crucial factor for provoking HV-EEG changes in a limited group of patients.