title: The effects of sevoflurane and nitrous oxide on middle cerebral artery blood flow velocity and transient hyperemic response.
abstract: We studied the effects of sevoflurane, with and without nitrous oxide, on the indices of cerebral autoregulation (transient hyperemic response ratio and the strength of autoregulation) derived from the transient hyperemic response (THR) test. Twelve patients (ASA physical status I or II) aged 18-40 yr presenting for routine non-neurosurgical procedures were recruited. The middle cerebral artery blood flow velocity was continuously recorded using transcranial Doppler ultrasonography. Preinduction THR tests were performed before the patients were anesthetized with alfentanil, propofol, and vecuronium. End-tidal carbon dioxide concentration and mean arterial pressure (to within 10% with a phenylephrine infusion) were maintained at their preinduction values. THR tests were performed sequentially at the following end-tidal sevoflurane concentrations: 2.2% in oxygen, 3.4% in oxygen, 3.4% with 50% nitrous oxide in oxygen, and 2.2% with 50% nitrous oxide in oxygen. Neither 2.2% nor 3.4% sevoflurane significantly affected cerebral autoregulation. The addition of 50% nitrous oxide to the 2.2%, but not the 3.4%, concentration of sevoflurane increased middle cerebral artery blood flow velocity and decreased autoregulatory indices significantly.
  
  
  CONCLUSIONS
  Transient hyperemic response is preserved during sevoflurane anesthesia but is significantly impaired when nitrous oxide is added to the lower concentration of sevoflurane (2.2%). These findings have implications for neurosurgical patients undergoing general anesthesia.
authors.affiliation: University Department of Anaesthesia and Intensive Care, Queen's Medical Centre and City Hospital NHS Trust, Nottingham, United Kingdom.
authors.forename: N M
authors.initials: NM
authors.lastname: Bedforth
authors.forename: K J
authors.initials: KJ
authors.lastname: Girling
authors.forename: J M
authors.initials: JM
authors.lastname: Harrison
authors.forename: R P
authors.initials: RP
authors.lastname: Mahajan
mesh_terms: D000293:Adolescent; D000328:Adult; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D001783:Blood Flow Velocity / Q000187:drug effects; D002536:Cerebral Arteries / Q000187:drug effects* / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D005260:Female; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D006940:Hyperemia / Q000139:chemically induced*; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology*; D009609:Nitrous Oxide / Q000494:pharmacology*; D000077149:Sevoflurane
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D009609:Nitrous Oxide