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NEUROSURGICAL ANESTHESIA

Nitrous Oxide Increases Normocapnic Cerebral Blood Flow Velocity but Does Not Affect the Dynamic Cerebrovascular Response to Step Changes in End-Tidal PCO₂ in Humans

Department of Anesthesiology, Chiba University School of Medicine, Chiba, Japan

Address correspondence and reprint requests to Dr. Jiro Sato, Department of Anesthesiology, Chiba University School of Medicine, 1-8-1 Inohana Chuo-ku, Chiba, 260-8670, Japan. Address e-mail to satoj{at}med.m.chiba-u.ac.jp

We sought to clarify the effect of nitrous oxide (N₂O) on the immediate responses of cerebral vasculature to sudden changes in arterial carbon dioxide tension in healthy humans. By use of a transcranial Doppler ultrasonography, blood flow velocity in the middle cerebral artery (V_MCA) was measured during a step increase followed by a step decrease in end-tidal CO₂ tension (PETCO₂) between normo- and hypercapnia while subjects inspired gas mixtures containing 70% O₂ + 30% N₂ (control) and 70% O₂ + 30% N₂O (N₂O) separately. During the control condition, both step increase and decrease in PETCO₂ produced rapid exponential changes in V_MCA. An increase in V_MCA produced by the step increase in PETCO₂ was smaller (P < 0.001) and slower (P < 0.001) than a decrease in V_MCA induced by the step decrease in PETCO₂. These general features of the dynamic cerebrovascular response were not affected by substitution of N₂O for N₂ in the inspired gases although N₂O increased baseline V_MCA by 15% (P < 0.001) compared with the control condition. We conclude that N₂O in itself does not affect the dynamic cerebrovascular response to arterial CO₂ changes, although it produces static mild cerebral vasodilation.

Implications: This study suggests that nitrous oxide does not affect the dynamic cerebrovascular reactivity to acute arterial carbon dioxide (CO₂) changes, i.e., exponential changes in cerebral blood flow in response to step changes in alveolar CO₂ tension, although it does produce a mild increase in normocapnic cerebral blood flow velocity.

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999