Supplementation of general anaesthesia with narcotic analgesics.

Four analgesic drugs--fentanyl, phenoperidine, morphine and pethidine--were compared in a double-blind trial involving 113 patients paralysed and ventilated with nitrous oxide and oxygen. The differences between the drugs were relatively small. There were only slight differences in "duration of action", a term which is questioned in this context. Pethidine appeared to have a slightly longer duration of action than the other drugs. The problems inherent in studying analgesics in this manner are discussed.