Hypnotics in infusion anaesthesia--with particular reference to thiopentone

Hypnotics are a group of drugs whose primary action is to produce unconsciousness. This contrasts to the opioids whose primary action is to reduce the sensation of pain and the tranquillisers whose primary action is to calm and to attenuate psychotic disease. Hypnotics of interest to the anaesthetist are the inhalational agents and intravenously administered drugs, including the barbiturates thiopentone and methohexitone, chlormethiazole, etomidate and propofol. Knowledge of the use of hypnotics to maintain anaesthesia is largely confined to the volatile anaesthetic agents, while knowledge of the use of the intravenous hypnotics is largely restricted to their use as intravenous induction agents and as sedative for regional procedures. The use of intravenous hypnotics to maintain anaesthesia requires careful control of infusion rates based on pharmacokinetic predictions. Once techniques are established, favourable operating conditions can be achieved, as well as acceptably short recovery times. With such techniques, the benefits of freedom from many of the adverse aspects of inhalational anaesthesia can be realised.