Xenon impairs neurocognitive and histologic outcome after cardiopulmonary bypass combined with cerebral air embolism in rats

Background: The neuroprotective properties of xenon may improve cerebral outcome after cardiac surgery using cardiopulmonary bypass (CPB). However, its disposition to expand gaseous bubbles that during CPB present as cerebral air emboli (CAE) could abolish any beneficial effect or even worsen cerebral outcome. Therefore, the authors studied the impact of xenon on neurologic, cognitive, and histologic outcome after CPB combined with CAE in rats. Methods: With institutional review board approval, 40 rats were assigned to four groups (n = 10). In two CPB-CAE groups, rats were subjected to 90 min of normothermic CPB with 10 repetitively administered CAEs (0.3 μl/bolus). Rats in two sham groups were not exposed to CPB and CAE. Groups were further subdivided into xenon (56%; 20 min before, during, and 30 min after CPB) and nitrogen groups. Neurologic and cognitive function was tested until postoperative day 14, when cerebral infarct volumes were determined. Results: Animals of the CPB-CAE groups showed transient deficits in gross neurologic function. Further, rats of the CPB-CAE-xenon group demonstrated impaired fine motor and cognitive performance persisting until postoperative day 14. Consistently, infarct volumes were larger in the CPB-CAE-xenon group compared with the CPB-CAE-nitrogen group (P = 0.03). Conclusions: Tills is the first demonstration in which the neurologic effects of CAE have been examined in a rat model of CPB. Xenon exposure aggravated the neurologic dysfunction that is produced by CAE during CPB; potential neuroprotective effects of xenon may have been masked by the effects of xenon on CAE.