Dexmedetomidine Effects on Brain Tissue Oxygenation Measured by Frequency Domain Near Infrared Spectroscopy

Dexmedetomidine (DEX) is a selective alpha2-adrenergic agonist that produces cerebral vasoconstriction. We used frequency domain near infrared spectroscopy (FD-NIRS) to study brain oxygenation during DEX intravenous bolus injection. Oxyhemoglobin (OHb), deoxyhemoglobin (HHb), brain oxygen saturation (SO2) and total hemoglobin (tHb) were acquired on the frontal right and left side in 4 neurosurgery patients without cerebral pathology. Measurements were performed using a portable brain oxymeter, Oxiplex TS (ISS, Champaign, IL). Dexmedetomidine 0.2 mcg/kg was given to attenuate hypertension during the initial stages of desflurane anesthesia. During DEX administration, regional cerebral OHb decreased from 17.7 ± 6.9 Mol/L to 16.1 ± 6.3 Mol/L (p < 0.05) and SO2 from 61 ± 12 % to 58 ± 12 % (p < 0.05). HHb did not change from 10.5 ± 2.8 Mol to 10.5 ± 2.7 Mol/L. Recovery of brain oxygenation to pre-DEX levels occurred within 5 minutes. After administration of DEX, a small but consistent decrease in OHb was observed, probably mediated by a local vasoconstrictor effect. Brain oxygenation decreased transiently with DEX treatment without an increase in HHb production.