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 ↑Hb and ↑ HbT, and ↓ HbO and ↓ SmcO₂ - will correlate with a theoretical asphyxia fingerprint-defined as ↓ SaO₂, ↑ PaCO₂, ↑ CBF and ↑ 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 (Hb), total hemoglobin (HbT), and mean cerebral tissue oxygen saturation (SmcO₂) - along with carotid blood flow (CaBF) measured by the transit time Doppler technique, and arterial oxygen saturation (SmcO₂) measured by pulse oximetry. RESULTS: Asphyxia induced ↓ PaO₂ and ↓ SaO₂, and an ↑ PaCO₂, ↑ MAP and ↑ CaBF. The Hamamatsu NIRO-500 CW spectrometer that we used readily detected cerebral hemoglobin changes: Hb and HbO dissociation occurred (↑ Hb and ↓ HbO) accompanied by ↑ HbT and ↓ SmcO₂. A close linear relationship and a good agreement between the changes in CaBF and Δ HbT existed (y = 0.3567x - 12.515; R² = 0.7177; r = 0.847; n = 218; p < 0.05), between the changes in Δ SmcO₂ and SaO₂ (y = 3.7467x + 93.314; R² = 0.8869; r = 0.941; n = 218; p < 0.05), as well as between Δ SmcO₂ and PaO₂. CONCLUSIONS: The present study demonstrated that optical variables HbT and SmcO₂ 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 "silver standard" to aid interpretations of optical signals in clinical settings where "gold standard" techniques are not available, i.g. in the human ferns and neonate.