Co-induction of anaesthesia: day-case surgery.

The term co-induction of anaesthesia has been applied to the use of two or more drugs to induce anaesthesia. The term was introduced in 1986 to describe the unplanned induction of anaesthesia by non-anaesthetically trained personnel practising sedation. A new benzodiazepine was combined with opioids, with synergistic effects, causing unplanned anaesthesia in an unsuitable environment leading to several fatalities. Currently, planned co-induction of anaesthesia is practised by anaesthetists exploiting drug interactions, particularly synergism, principally between midazolam, fentanyl, sufentanil and alfentanil, and propofol. It can produce an improvement in all phases of anaesthesia, including induction, maintenance and recovery. There are advantages in combining midazolam with propofol, thereby reducing the risk of awareness and also the dose of propofol and hence its side-effects and cost. Propofol is the principal intravenous induction agent for day-case anaesthesia. The pre-administration of 0.03 mg kg-1 of midazolam (approximately 2 mg in normal healthy adults) is now being practised widely. Current papers suggest that 2 mg of midazolam administered to an average, otherwise healthy, adult does not compromise recovery, whereas an increase to 5 mg may be expected to delay the possibility of final discharge of such patients by about 20 min. The use of midazolam and propofol with or without either fentanyl or alfentanil is probably the principal technique for the induction of day-case anaesthesia at the present time. A major advantage is that by reducing the dose of propofol there is less chance of the severe bradycardia that is sometimes associated with the combined use of propofol and opioids, although this can be prevented by vagolytic agents. However, the use of opioids increases the incidence of post-operative nausea and vomiting. Another important drug is ketamine, the effects of which are often additive with other drugs. The combination of ketamine and midazolam is an important technique, particularly in the management of critically ill patients. The alpha 2-agonists, e.g. clonidine and dexmedetomidine, may also have a role in this context in the future. This paper presents the current approach to the co-induction of anaesthesia, particularly in relation to the reduced risk of awareness when using midazolam, and the health economics in relation to the potential reduction in the dose and hence cost of propofol.