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.