Effect of baricity on spinal anaesthesia with amethocaine

Amethocaine 1% solution was mixed with equal volumes of water, 0.9% saline or 10% dextrose to prepare respectively, hypobaric, isobaric and hyperbaric solutions which were compared for intradural spinal anaesthesia in 60 patients. Thirty patients received 10 mg and 30 patients received 15 mg of amethocaine. Injections were made with the patients in the lateral recumbent position and the operating table was horizontal during and after injection. Equal numbers of patients and equal numbers of males and females received hypobaric, isobaric and hyperbaric solutions. The mean spread of analgesia after the hyperbaric solution was five dermatomes greater than after the other two solutions, but the extent of analgesia was not significantly different whether amethocaine 10 mg or 15 mg was injected. The mean duration of analgesia after the hyperbaric solution was 285 min compared with 332 min and 360 min after the isobaric and hypobaric solutions respectively. The mean duration of analgesia after amethocaine 15 mg was significantly greater than after 10 mg.