Key result
Adding 50% nitrous oxide to 2.2% sevoflurane significantly impaired cerebral autoregulation and increased middle cerebral artery blood flow velocity, whereas adding it to 3.4% sevoflurane did not.
Why the study?
Does the addition of nitrous oxide to sevoflurane affect middle cerebral artery blood flow velocity and cerebral autoregulation in patients undergoing non-neurosurgical procedures?
Does the addition of nitrous oxide to sevoflurane affect middle cerebral artery blood flow velocity and cerebral autoregulation in patients undergoing non-neurosurgical procedures?
Adding nitrous oxide to a lower concentration of sevoflurane impairs cerebral autoregulation, which has implications for neurosurgical patients.
Nitrous oxide addition to low-dose sevoflurane may impair autoregulation; hypothesis-generating for neurosurgical anesthesia and needs prospective validation.
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. Implications: 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. (Anesth Analg 1999;89:170-4)
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Bedforth et al. (1999) studied Routine non-neurosurgical procedures (n=12). Sevoflurane and nitrous oxide vs. Preinduction baseline and between concentrations was evaluated on Middle cerebral artery blood flow velocity and indices of cerebral autoregulation. Adding 50% nitrous oxide to 2.2% sevoflurane significantly impaired cerebral autoregulation and increased middle cerebral artery blood flow velocity, whereas adding it to 3.4% sevoflurane did not.
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