Seizure susceptibility during recovery from hypercapnia in neonatal dogs.

Seizure susceptibility during recovery from hypercapnia was investigated in seven anesthetized neonatal dogs; 13, 20, or 30% CO2 gas was administered for 30 min through a ventilator to result in three levels of hypercapnia in which measured PaCO2 values were approximately 70, 100, and 140 mm Hg. Thereafter, the animals were allowed to recover for 45 min; during this recovery phase, electrocorticography was performed. In five of seven dogs, approximately 1.5 Hz slow irregular spike and wave bursts appeared at 6 min after abrupt withdrawal from hypercapnia and lasted several minutes. This seizure activity was followed by a brief period of electrical suppression. This phenomenon was most often observed during the recovery from moderate hypercapnia and between the PaCO2 values of 100 and 50 mm Hg. When seizure activities appeared in the electrocorticogram, arterial blood pressure increased -40 mm Hg from the preseizure level. These results suggest that neonatal seizures may occur during recovery from hypercapnia.