Influence of nitrous oxide on minimum alveolar concentration of sevoflurane for laryngeal mask insertion in children.
BACKGROUND
Inhalational induction with sevoflurane and nitrous oxide is frequently used for Laryngeal Mask Airway (LMA; Laryngeal Mask Company, Henley-on-Thames, United Kingdom) insertion in children. The authors determined the influence of nitrous oxide on the minimum alveolar concentration (MAC) of sevoflurane for LMA insertion.


METHODS
One hundred twenty unpremedicated children (age, 1-9 yr; American Society of Anesthesiologists physical status I) were randomly assigned to receive 1 of 15 end-tidal concentrations of nitrous oxide and sevoflurane for inhalational induction via a facemask: 0% nitrous oxide with 1.2, 1.4, 1.6, 1.8, or 2.0% sevoflurane; 33% nitrous oxide with 0.8, 1.0, 1.2, 1.4, or 1.6% sevoflurane; or 67% nitrous oxide with 0.4, 0.6, 0.8, 1.0, or 1.2% sevoflurane. The LMA was inserted after steady state end-tidal anesthetic concentrations had been maintained for 15 min. The response to insertion was recorded by three independent blinded observers. The interaction between nitrous oxide and sevoflurane was determined using logistic regression analysis.


RESULTS
The MAC of sevoflurane for LMA insertion (95% confidence limit) was 1.57% (1.42-1.72%), and the concentration of sevoflurane required to prevent movement in 95% of children was 1.99% (1.81-2.57%). The addition of 33% and 67% nitrous oxide linearly decreased the MAC of sevoflurane for LMA insertion by 22% and 49%, respectively (P < 0.001). The interaction coefficient between nitrous oxide and sevoflurane did not differ from zero (P = 0.7843), indicating that the relation was additive.


CONCLUSIONS
Nitrous oxide and sevoflurane suppress the responses to LMA insertion in a linear and additive fashion in children.
Department of Anesthesia, Mito Saiseikai General Hospital.
Shinichi
S
Kihara
Yuichi
Y
Yaguchi
Shinichi
S
Inomata
Seiji
S
Watanabe
Joseph R
JR
Brimacombe
Noriko
N
Taguchi
Tetsuya
T
Komatsuzaki
D000465:Algorithms; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000493:pharmacokinetics; D002648:Child; D002675:Child, Preschool; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007223:Infant; D017214:Laryngeal Masks; D016015:Logistic Models; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage; D016343:Monitoring, Intraoperative; D009068:Movement / Q000187:drug effects; D009609:Nitrous Oxide / Q000008:administration & dosage / Q000493:pharmacokinetics; D011650:Pulmonary Alveoli / Q000378:metabolism*; D000077149:Sevoflurane; D016037:Single-Blind Method
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D009609:Nitrous Oxide