Nitrous oxide is a widely used anesthetic agent. The mechanism of its central action is not completely understood and its importance is questioned.~Total intravenous anesthesia can be driven by a computer using bispectral index as a controller. Such a system matches anesthetic agent requirements to the needs of each individuum and thus allows an unbiased evaluation of the influence of nitrous oxide. Two groups of patients are compared: one ventilated with a oxygen-air mixture and one with oxygen-nitrous oxide mixture. Anesthesia is provided by a dual-loop which adapts propofol and remifentanil target concentrations to maintain a bispectral index between 40 and 60 in both groups.
The main objective of the study is to analyze the influence of nitrous oxide on propofol and remifentanil requirements.