Monitoring of immature rabbit brain during hypoxia with near-infrared spectroscopy.

Continuous monitoring of the cerebral blood flow, oxyhemoglobin, deoxyhemoglobin, total hemoglobin, oxidized cytochrome a, a3, and tissue pH during prolonged CO2 or N2 loading in 2-week-old rabbits was performed by near-infrared spectroscopy, the thermocouple method, and a tissue pH meter. Near-infrared spectroscopy demonstrated decreases in oxyhemoglobin and oxidized cytochrome a, a3 and increases in deoxyhemoglobin and total hemoglobin in the early stage within 5 min, which gradually lessened with time on both 10% concentration of inspired O2 with CO2 and N2. CBF increased with venous retention in the early stage and then slowly decreased in parallel with blood pressure and oxidized cytochrome a, a3 on abolition of autoregulation. These changes were more remarkable during the 10% concentration of inspired O2 with CO2 than N2 which may be caused by marked acidosis and hypotension associated with hypercarbia. Oxidized cytochrome a, a3, however, demonstrated a gradual decrease in 10% concentration of inspired O2 with N2 rather than CO2; therefore, the continuous monitorings demonstrated hemodynamic and oxygenation changes despite the same extent of prolonged hypoxic loading. These changes in prolonged hypoxic conditions may occur in human intrapartum asphyxia which develops into postnatal hypoxic-ischemic encephalopathy.