The effect of adding nitrous oxide on MAC of sevoflurane combined with two target-controlled concentrations of remifentanil in women.
OBJECTIVE
The aim of this prospective, randomized, double-blind study was to determine the effects of adding nitrous oxide on sevoflurane requirement for blunting sympathetic responses after surgical incision combined with two different target-controlled concentrations of remifentanil (1 and 3 ng mL(-1)) in female.


METHODS
102 female patients, aged 20-50 yr, ASA I, undergoing general anaesthesia for elective abdominal surgery were enrolled and randomly allocated to receive sevoflurane anaesthesia alone (Group A, n=53), or with the addition of 60% nitrous oxide (Group N, n=49). Patients of both groups were further assigned to receive a target-controlled remifentanil infusion with an effect-site concentration of either 1 ng mL(-1) (Group N1, n=27; Group A1, n=30), or 3 ng mL(-1) (Group N3, n=22; Group A3, n=23). Sympathetic responses to surgical incision were determined after a 20-min period of stable end-tidal sevoflurane and target-controlled remifentanil concentrations. Predetermined end-tidal sevoflurane concentrations and minimum alveolar concentration (MAC) for each group were determined using an up-and-down sequential allocation technique.


RESULTS
The MAC of sevoflurane was 3.96% (95% confidence interval, CI95: 3.69-4.23%) in Group A1 and 1.2% (CI95: 0.9-1.3%) in Group N1 (P < 0.01), while in Groups A3 and N3 the MAC of sevoflurane was 0.36% (CI95: 0.24-0.47%) and 0.18% (CI95: 0.1-0.3%), respectively (P < 0.05).


CONCLUSIONS
Adding 60% nitrous oxide reduces the MAC of sevoflurane by 70% when using a remifentanil concentration of 1 ng mL(-1) and 50% when using a remifentanil concentration of 3 ng mL(-1).
Vita-Salute University of Milano, Department of Anesthesiology, IRCCS H, San Raffaele, Milan, Italy. albertin.andrea@hsr.it
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Albertin
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Casati
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Bergonzi
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Moizo
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Lombardo
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Torri
D000328:Adult; D000768:Anesthesia, General; D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous / Q000008:administration & dosage / Q000493:pharmacokinetics; D001794:Blood Pressure / Q000187:drug effects; D004311:Double-Blind Method; D016503:Drug Delivery Systems; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D016015:Logistic Models; D008738:Methyl Ethers; D009609:Nitrous Oxide; D010880:Piperidines / Q000008:administration & dosage / Q000493:pharmacokinetics; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000378:metabolism*; D000077208:Remifentanil; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D008738:Methyl Ethers; D010880:Piperidines; D000077149:Sevoflurane; D009609:Nitrous Oxide; D000077208:Remifentanil