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NEUROSURGICAL ANESTHESIA

Measuring Cerebral Oxygenation During Normobaric Hyperoxia: A Comparison of Tissue Microprobes, Near-Infrared Spectroscopy, and Jugular Venous Oximetry in Head Injury

Andrew D. McLeod, FRCA^*, Farrell Igielman, FRCA^*, Clare Elwell, PhD, Mark Cope, PhD, and Martin Smith, FRCA^*

Departments of *Neuroanaesthesia and Medical Physics & Bioengineering, The National Hospital for Neurology and Neurosurgery, University College London Hospitals & Centre for Anaesthesia, UCL, London, United Kingdom

Address correspondence and reprint requests to M. Smith, FRCA, Department of Neuroanaesthesia, Box 30, The National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK. Address e-mail to martin.smith{at}uclh.org

We measured simultaneous changes in jugular venous oxygen saturation, brain tissue oxygen tension, and cerebral tissue oxygen index by using near-infrared spectroscopy during normobaric hyperoxygenation in eight severely brain-injured patients. Patients were ventilated at their baseline fraction of inspired oxygen (FIO₂), followed by stepped changes in FIO₂ to 1.0, 0.6, and 0.02–0.05 less than baseline. There was an increase (P < 0.01) in jugular venous saturation (mean ± SD) from a baseline value of 79% ± 7% to 89% ± 6% and 84% ± 8% at an FIO₂ of 1.0 and 0.6, respectively. The changes in brain tissue oxygen tension were from a baseline of 30 ± 5 mm Hg to 147 ± 36 mm Hg and 63 ± 6 mm Hg at an FIO₂ of 1.0 and 0.6, respectively (P < 0.01). The baseline tissue oxygen index was 78% ± 3%, and this increased to 83% ± 5% and 80% ± 4% at an FIO₂ of 1.0 and 0.6, respectively. There was a reduction (P < 0.05) in tissue oxygen index to 76.2% ± 3.0% when the FIO₂ was reduced to less than baseline. The changes in the three variables followed similar patterns but varied in their degree and speed of response. During brain injury, FIO₂ affects measured variables of cerebral oxygenation.

IMPLICATIONS: We compared simultaneous measurements of jugular venous saturation, brain tissue oxygen tension, and cerebral tissue oxygen index during normobaric hyperoxia in brain-injured patients. PaO₂ influences the output of monitors of cerebral oxygenation, but this does not necessarily equate to improved brain oxygenation.

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