Extradural analgesia in obstetrics: a controlled trial of carbonated lignocaine and bupivacaine hydrochloride with or without adrenaline.

Four local anaesthetic solutions (2% carbonated lignocaine with or without adrenaline and 0.5% bupivacaine HCl with or without adrenaline) were used randomly for 335 continuous lumbar extradural blocks in labour. Carbonated lignocaine caused a more rapid onset of analgesia than bupivacaine HCl. The addition of adrenaline made little difference to the onset times, prolonged markedly the duration of analgesia with carbonated lignocaine and had little effect on the duration of analgesia with bupivacaine HCl. Tachyphylaxis was a feature with carbonated lignocaine and adrenaline, but not with the other solutions. The incidence of unblocked segments was 7-9% in the four groups. The incidence of unilateral analgesia was 6% with plain lignocaine and 13% in the other groups. Complete pain relief occurred more frequently with bupivacaine HCl than with carbonated lignocaine and the use of adrenaline had little effect on the degree of analgesia.