ISPUB.COM The Internet Journal of Neuromonitoring Volume 5 Number 1 1 of 6 Dexmedetomidine Effects on Brain Tissue Oxygenation Measured by Frequency Domain Near Infrared Spectroscopy R Gatto, W Hoffman, C Paisansathan, V Baughman, F Charbel Citation R Gatto, W Hoffman, C Paisansathan, V Baughman, F Charbel. Dexmedetomidine Effects on Brain Tissue Oxygenation Measured by Frequency Domain Near Infrared Spectroscopy. The Internet Journal of Neuromonitoring. 2006 Volume 5 Number 1. Abstract 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. INTRODUCTION Dexmedetomidine (DEX) is a selective alpha 2 -adrenergic agonist with sedative and analgesic effects [ 1 , 2 ]. DEX enhances anesthesia produced by other anesthetic drugs and decreases blood pressure by stimulating central alpha2 and imidazoline receptors [ 3 , 4 ]. The use of DEX in neuroanesthesia generate a reduction in the sympathetic tone and a decrease in peripheral noradrenaline release reducing hypertensive responses to neurosurgical patient stimulation during catheterization and head pin holder application. However, initially direct activation of cerebral α 2b receptors produces local vasoconstriction effect that leads to a transient increase in arterial blood pressure and a decrease in cerebral blood flow [ 5 , 6 ]. A common problem during neurosurgical procedures is the interference of anesthetic drug during intraoperative action potential recording. DEX has been used as an elective anesthetic drug in awake craniotomy during resection of brain lesions in eloquent areas in order to decrease anesthetic use without attenuating neuronal function [ 7 ]. Procedures performed with intraoperative feedback from the patient reduced the morbidity associated with surgical treatment of critical brain areas. A rapid restoration in the level of consciousness in the postoperative period without respiratory depression and significant cognitive impairment has popularized the use of this drug in intensive care units [ 2 ]. In previous studies, a neuroprotective mechanism has been described with the use of DEX [ 8 ], that may be related to a reduction in the release of catecholamine during cerebral hypoxic-ischemia [ 9 ]. However, this may conflict with other reports that DEX produces direct cerebral vasoconstriction and may decrease brain oxygen delivery[ 10 ]. Quantitative brain tissue oxygenation monitoring has been established in animals using frequency domain near infrared spectrometry method (FD-NIRS) [ 11 ], and more recently in clinical studies [ 12 ]. As opposed to continuous wave methods of brain tissue oxygenation monitoring, FD-NIRS utilizes spatially resolved frequency domain information to measure absolute absorption and scattering of near infra-red light and calculate absolute concentrations of oxyhemoglobin (OHb) and deoxyhemoglobin (HHb) in brain tissue. The purpose of this investigation was to determine if brain oxygenation decreased during the initial period of DEX