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NEUROSURGICAL ANESTHESIA

Measuring Hemoglobin Oxygen Saturation During Graded Hypoxic Hypoxia in Rat Striatum

Cécile Julien, PhD^*, Adrian Bradu, PhD, Raphaël Sablong, PhD, Emmanuelle Grillon, MSc^*, Chantal Remy, PhD^*, Jacques Derouard, PhD, and Jean-François Payen, MD, PhD^*

*INSERM UM 594, Neuroimagerie Fonctionelle et Métabolique, and Laboratoire de Spectrométrie Physique, Université Joseph Fourier, and Département d’Anesthésie-Réanimation, Hôpital Albert Michallon, Grenoble, France

Address correspondence and reprint requests to Jean-François Payen, Unité Mixte INSERM/UJF 594, LRC CEA 30V, Pavillon B, BP 217, Hôpital Albert Michallon, F-38043 Grenoble, France. Address e-mail to jfpayen{at}ujf-grenoble.fr.

We evaluated in vivo reflectance spectroscopy of visible light as a method to assess brain tissue hemoglobin oxygen saturation in rat striatum (SstrO₂). Seven anesthetized and mechanically ventilated rats were subjected to incremental reduction in the fraction of inspired oxygen (Fio ₂): 0.35, 0.25, 0.15, 0.12, and 0.10, followed by a reoxygenation period (Group 1). At each episode, local changes in SstrO₂ and in cerebral blood flow (LCBF) were simultaneously determined in the two striatal regions, using reflectance spectroscopy and laser Doppler flowmetry, respectively. Another group of rats (Group 2, n = 6) was also studied to measure sagittal sinus blood hemoglobin saturation (SssO₂) during graded hypoxic hypoxia. Corpus striatum exhibited a significant graded decrease in SstrO₂, from 38% ± 17% at Fio₂ of 0.35 (control) to 16% ± 10% at Fio₂ of 0.12 and to 13% ± 7% at Fio₂ of 0.10 (P < 0.05), with no difference between the two hemispheres. These local changes in SstrO₂ were associated with a significant graded increase in LCBF: 161% ± 26% of control values and 197% ± 34% during these 2 hypoxic episodes, respectively (P < 0.05). All local changes were fully reversed during the reoxygenation period. In Group 2, SssO₂ decreased from 38% ± 8% at Fio₂ of 0.35 (control) to 10% ± 3% at Fio₂ of 0.10, closely related to SstrO₂ decreasing in hypoxia. This study shows that reflectance spectroscopy of the visible light in rat striatum could be a possible measure of continuous changes in SstrO₂. SssO₂ and LCBF measurements during graded hypoxic hypoxia indicate that changes in SstrO₂ reflect primarily those in brain venous oxygenation.