Comparative anaesthetic properties of various local anaesthetic agents in extradural block for labour

Various concentrations of lignocaine, etidocaine and bupivacaine in 10-ml doses of plain solutions were studied in a double-blind manner as agents for extradural analgesia to relieve the pain of labour. In 67 patients in established labour the onset time and duration of analgesia were assessed by the abolition and recurrence of the pain of uterine contractions, motor block on a 0-2 scale, dermatomal spread by pinprick testing, and arterial pressure by standard sphygmomanometry. Increasing the drug concentration reduced the onset times and increased both the duration of analgesia and the degree of motor block, but had little effect on dermatomal spread or on the frequency of hypotension. Based on the results the agents have been classified with regard to onset and duration of analgesia and degree of motor blockade.