Effect of Nitrous Oxide on Intravenous Closed-loop Anesthesia

Anesthésie Totale Intraveineuse en " Boucle d'Asservissement " guidée Par l'Index Bispectral : Effet de l'Adjonction de Protoxyde d'Azote (Effect of Nitrous Oxide on Intravenous Closed-loop Anesthesia)

The main objective of the study is to analyze the influence of nitrous oxide on propofol and remifentanil requirements.

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.

Inclusion Criteria:

• General anaesthesia with controlled ventilation

Exclusion Criteria:

• Age lower than 18 years
• Pregnant woman
• Allergy to the propofol or to a muscle myorelaxant
• Patients receiving a psychotropic treatment
• Presence of a central neurological disorder or a lesion cerebral
• Patients having an anomaly of blood cells count preoperative biological assessment
• Patients having had an anaesthesia in the previous month