Techniques of inhalational analgesia in the postoperative period.

Subanaesthetic concentrations of ether, trichloroethylene, cyclopropane and nitrous oxide can provide analgesia (Dundee, Nicholl and Black, 1962). This property of ether (Artusio, 1955) and cyclopropane (Sheiner, 1958) has been applied to the production of analgesia for surgical procedures but only nitrous oxide and trichloroethylene have been used for postoperative analgesia. Nitrous oxide has been used more widely. Two different methods have been employed. Low concentrations, 20-25 per cent, will produce moderate analgesia similar to, or greater than, that from narcotics (Chapman, Arrowood and Beecher, 1943; Parbrook, Rees and Robertson, 1964). Slight sedation may accompany the analgesia but other side effects are avoided. High concentrations, of about 50-70 per cent produce the somnolent state of "analgesic anaesthesia" (Federmesser, 1962). This level is considered in greater detail later.