Comparison of cerebro vascular reactivity to carbon dioxide at equi MAC doses of Isoflurane and sevoflurane in neonates (Varis study): A randomised controlled study

Inhaled anaesthetics increase the Cerebral Blood Flow and affects cerebrovascular reactivity  to CO2,  largely maintained till 1 minimum alveolar concentration (MAC).  The cerebral vasodilatory effects of inhaled anaesthetic agents are far more pronounced in children as compared to adult population. Sevoflurane and Isoflurane do not have similar effects on cerebral circulation. Sevoflurane is a less potent cerebral vasodilator and preserves the dynamic Cerebral Autoregulation as compared to isoflurane when administered in equal MAC doses. Study in adults have suggested that Isoflurane preserves the cerebro vascular reactivity to carbon dioxide upto 1 MAC, whereas sevoflurane has been shown not to have effect within a range of 0.5-1 MAC.However, there is no data on effect of anaesthetic agents on cerebro vascular reactivity to carbon dioxide in neonates. We hypothesized that sevoflurane would preserve the cerebro vascular reactivity to carbon dioxide  better than isoflurane in neonates undergoing non cardiac surgery under GA at equal MAC doses when the End Tidal carbon dioxide (EtCO2) changes from 35 mmHg to 45 mmHg.