Monitoring of cerebral hemodynamics and oxygenation by continuous wave optical spectroscopy during asphyxia in newborn piglets

OBJECTIVE: To investigate whether an optical asphyxia fingerprint - defined as up arrow Hb and up arrow HbT, and down arrow HbO and down arrow SmcO(2) - will correlate with a theoretical asphyxia fingerprint - defined as down arrow SaO(2), up arrow PaCO2, up arrow CBF and up arrow MAP. METHODS: Ten newborn piglets underwent short reversible asphyxial episodes. Cerebral hemodynamics and oxygenation had been monitored by optical spectroscopy - measures changes in oxyhemoglobin (HbO), deoxyhemoglobin (Kb), total hemoglobin (HbT), and mean cerebral tissue oxygen saturation (SmcO(2))-along with carotid blood flow (CaBF) measured by the transit time Doppler technique, and arterial oxygen saturation (SmcO(2)) measured by pulse oximetry. RESULTS: Asphyxia induced down arrow PaO2 and down arrow SaO(2), and an up arrow PaCO2, up arrow MAP and up arrow CaBF. The Hamamatsu NIRO-500 CW spectrometer that we used readily detected cerebral hemoglobin changes: Hb and HbO dissociation occurred (up arrow Hb and down arrow HbO) accompanied by up arrow HbT and down arrow SmcO(2). A close linear relationship and a good agreement between the changes in CaBF and Delta HbT existed (y = 0.3567x - 12.515; R-2 = 0.7177; r = 0.847; n = 218; P < 0.05), between the changes in Delta SmcO(2) and SaO(2) (y = 3.7467x + 93.314; R-2 = 0.8869; r = 0.941; n = 218; p < 0.05), as well as between Delta SmcO(2) and PaO2. CONCLUSIONS: The present study demonstrated that optical variables HbT and SmcO(2) can be used to monitor changes in cerebral hemodynamics and oxygenation during asphyxia. Unfortunately none of the individual optical variables alone could be used to monitor changes in cerebral hemodynamics and oxygenation under a variety of possible clinical circumstances. However, all variables together, forming patterns unique to the commonly occurring physiological conditions, might potentially serve as a "sliver standard" to aid interpretations of optical signals in clinical settings where "gold standard" techniques are not available, i.g. in the human fetus and neonate.