Validation in Volunteers of a Near-Infrared Spectroscope for Monitoring Brain Oxygenation h Vim Valerie Pollard, FFARCSP, Donald S. Prough, MD*, A. Eric DeMelo, FRCA*, Donald J. Deyo, DVM*, Tatsuo Uchida, MS*, and Hugh F. Stoddart, Bst *Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas and tsomanetics Corporation, Troy, Michigan Cerebral oximeters based on near-infrared spectros- copy may provide a continuous, noninvasive assess- ment of cerebral oxygenation. We evaluated a proto- type cerebral oximeter (Invos 3100; Somanetics, Troy, MI) in 22 conscious, healthy volunteers breathing hy- poxic gas mixtures. Using the first 12 subjects (train- ing group), we developed an algorithm based on the mathematic relationship that converts detected light from the field surveyed by the probe to cerebral he- moglobin oxygen saturation (C&o,). To develop the al- gorithm, we correlated the oximeter result with the es- timated combined brain hemoglobin oxygen saturation (CScombo2, where CScombo2 = Sao2 X 0.25 + Sjo2 X 0.75 and So7 = iugular venous saturation). We then vali- dated’ the alg&ithm in the remaining 10 volunteers (validation group). A close association (u2 = 0.798- 0.987 for individuals in the training group and Y’ = 0.794-0.992 for individuals in the validation group) ex- isted between C&o, and CS,,,o,. We conclude that continuous monitoring with cerebraloximetry may ac- curately recognize decreasing cerebral hemoglobinox- ygen saturation produced by systemic hypoxemia. (Anesth Analg 1996;82:269-77) T he brain is critically dependent on adequate ox- ygenation for function and viability. Routine clinical assessment of cerebral oxygen delivery has been limited to measurement of blood pressure and analysis of arterial oxygenation by pulse oximetry or arterial blood gases. Recent interest has focused on the use of jugular venous bulb blood oxygen tension and content (11, which reflect the overall adequacy of cerebral oxygen delivery but do not provide an accu- rate indication of local cerebral perfusion. Moreover, jugular venous bulb catheterization is an invasive technique. Noninvasive in vivo spectroscopy provides an assess- ment of regional brain hemoglobin oxygen saturation by measuring the differential absorption of near-infrared light. It has been studied extensively in animals (2-6) and is widely used as a technique for continuously mon- itoring brain oxygenation in neonates (7-9). Cerebral oximetry has also been evaluated in adults under anes- thesia (10) and has been used to assess the adequacy of This research was sponsored in part by a grant from Somanetics Corp., Troy, MI. Presented in part at the International Anesthesia Research Soci- ety, Orlando, FL, March 1994. Accepted for publication September 15, 1995. Address correspondence and reprint requests to Valerie Pollard, FFARCSI, Department of Anesthesiology, The University of Texas Medical Branch, Galveston, TX 77555-0591. 01996 by the International Anesthesia Research Society 0003-2999/96/$5.00 collateral circulation in patients undergoing carotid end- arterectomy (11). The spectroscopic signal changes as quickly in response to progressive cerebral hypoxia as the electroencephalogram (12,13). Validation of in vivo spectroscopy has been limited by the lack of a “gold standard” against which to compare the generated signal. The saturation meas- ured by the oximeter originates in a local field con- taining arteries, veins, and capillaries, with a predom- inantly venous contribution (70%-80%) (2,12,14,15). The cerebral oximeter produces multiple signals that are then processed (the “algorithm”) to determine the average oxygen saturation of hemoglobin in the field C&o,, where CS stands for cerebral saturation and f stands for field. Using graded hypoxia in volunteers, we adjusted the coefficients of the algorithm to maximize the correlation of its result with the estimated combined cerebral saturation (CScombo2 = 0.25 S,o, + 0.75 Sjo,), where comb stands for combined, $0, is the measured arterial saturation, and Sjo2 is the measured jugular ve- nous bulb saturation. We then validated this coefficient set in a second group of volunteers. Methods Description of the Cerebral Oximeter Cerebral spectroscopy uses near-infrared light of wavelengths ranging from 700 to 1000 nm. The Invos Anesth Analg 1996;82:269-77 269