CO2 reactivity of the cerebral hemoglobin concentration in healthy term newborns measured by near infrared spectrophotometry

CO2 reactivity of cerebral hemoglobin concentration was studied in 16 healt hy term neonates on days 1 and 4 after birth using the near infrared spectr ophotometry (NIRS) technique. The aim was to establish data on the physiolo gical range of CO2 reactivity in healthy newborns and to investigate the in fluence of postnatal age on it. The CO;! reactivity measured by NIRS is exp ressed as the change of the total cerebral hemoglobin concentration (tHbR) per change of CO;! tension in mu mol/l/kPa. We evaluated COP reactivity dur ing increases and decreases of transcutaneous CO2 partial pressure and foun d in our methodological setting the data of the increases more reliable. In all infants but 1 we found a tHbR on day 1 with a mean value of 8.19 mu mo l/l/kPa (-1.39 to 18.87), in all infants on day 4 with a mean value of 9.54 mu mol/l/kPa (2.76-25.88). There is a trend to higher values between day 1 and day 4 (difference = 2.25 mu mol/l/kPa; p = 0.08). The noninvasive NIRS technique enabled us to test the cerebrovascular CO2 reactivity of the tHb R for the first time in healthy term newborns. Data on its physiologic rang e and variability are presented and compared to findings from ventilated in fants and other age groups. As the CO2 reactivity might be an indicator for infants at risk of cerebral damage, it is necessary to have data on the ph ysiological range of this parameter.