Neonatal sensors

After birth, cerebral oxygen saturation (r_cSO₂) was measured with the INVOS 5100c spectrometer (Medtronic, Dublin, Ireland) with neonatal sensors (Medtronic), placed on the frontoparietal side of the forehead. First, r_cSO₂ was measured daily for at least two consecutive and stable hours during the first 3 days after birth starting immediately after stabilization of the infant on the NICU. Preferably, the measurements were performed at the same time each day to avoid possible effects of diurnal variation. Second, r_cSO₂ was measured during every corrective/palliative surgical procedure within the first 3 months after birth. Third, r_cSO₂ was measured for 24 hours following each invasive cardiac procedure within the first 3 months after birth. Simultaneously with r_cSO₂ measurements, we measured preductal arterial oxygen saturation (SpO₂) and calculated cerebral fractional tissue oxygen extraction (FTOE). For statistical purposes, we selected representative two-hour periods of stable r_cSO₂ measurements, preferably at the same time during the day, and calculated mean r_cSO₂ and FTOE for each of the first 3 days after birth. In addition, we calculated mean r_cSO₂ and FTOE during cardiac surgery and for 24 hours after cardiac surgery. Furthermore, we assessed the burden of hypoxia in two ways (percent of time <60% and percent of time <50%) and r_cSO₂ nadir during cardiac surgery.