Monitoring of oxygenation:
Arterial Oxygen saturation (SpO2) was monitored using the Masimo Rad 7 Massimo® (Massimo Corporation, Irvine, California) pulse oximeter; Cerebral regional tissue oxygen (crRTO) was measured by NIRS (FORE-SIGHT®Absolute Tissue Monitor, Casmed®, Branford, CT). The sensor was applied to the frontal area of the head; fractional oxygen extraction (FOE)(22) was defined physiologically as the ratio between oxygen delivery and regional oxygen consumption using NIRS(23),(24), calculated as FOE = (SpO2 – RTO) / SpO2 (all expressed as fractions). The Oxygen saturation index (OSI)(25) = MAP × FiO2 × 100/ SpO2 was used as a marker of the severity of HRF in each studied patient, and SpO2: FiO2 ratio was corrected with crRTO.