Nitrous oxide produces a non-linear reduction in thiopentone requirements.
We studied 88 healthy, ASA I patients (aged 20-45 yr), to determine if nitrous oxide affects thiopentone requirements for achieving 50% probability of no movement in response to verbal commands (CP,50). Patients were allocated randomly to one of four nitrous oxide concentration groups (0%, 20%, 40% and 60%). Patients in each group were also allocated randomly to receive predetermined target plasma concentrations of thiopentone. Computer-controlled continuous infusion was used to maintain the target plasma thiopentone concentration, and this concentration was held constant for 6 min to ensure equilibration. The CP,50, value of thiopentone in the absence of nitrous oxide was 14.8 micrograms ml-1. The reduction in CP,50 by nitrous oxide was non-linear, and the interaction coefficient between nitrous oxide and thiopentone was significantly smaller than zero (P = 0.0274), indicating that nitrous oxide antagonized the ability of thiopentone to prevent response to verbal commands.
Katoh
T
T
Department of Anaesthesiology and Intensive Care Medicine, Hamamatsu University School of Medicine, Japan.
Ikeda
K
K
D000328:Adult; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000008:administration & dosage* / Q000037:antagonists & inhibitors / Q000097:blood; D001307:Auditory Perception / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D009609:Nitrous Oxide / Q000008:administration & dosage / Q000494:pharmacology*; D013874:Thiopental / Q000008:administration & dosage* / Q000037:antagonists & inhibitors / Q000097:blood
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D013874:Thiopental; D009609:Nitrous Oxide