Role of pulmonary edema in phasic changes of cerebral oxygenation during serial seizures

To examine whether pulmonary dysfunction leads to episodes of cerebral hypoxia during recurrent seizures, measurements were made of arterial blood pressure, blood-gases, cerebral pO2, and relative changes in cytochrome a,a3 redox levels in anesthetized, paralyzed rats. Seizures were induced serially with bicuculline (BIC) or pentylenetetrazol (PTZ). During early seizures, cerebral oxygenation increased phasically. As seizures continued, a transition often occurred following which seizures were accompanied by phasic decreases in cerebral oxygenation. In addition, pulmonary edema often occurred at an unpredictable point during a series of seizures. Seizure-associated pulmonary edema was less likely to occur with pentobarbital anesthesia and PTZ seizures, than with nitrous oxide anesthesia and BIC seizures. Pulmonary edema was always accompanied by prolonged increases in blood pressure and paroxysmal electrocortical activity, and by hypoxemia, acidemia, and decreased cerebral oxygen supply. Despite the severity of these physiological changes, the transition from phasic increases to decreases in cerebral oxygenation during serial seizures occurred with virtually the same frequency in rats with and without pulmonary edema. This indicates that this transition is independent of pulmonary edema.