EFFECT OF INJECTED VOLUME AND SPEED OF INJECTION ON THE SPREAD OF SPINAL ANAESTHESIA WITH ISOBARIC AMETHOCAINE

Amethocaine 10 mg in isobaric solution was injected intrathecallyin 40 patients. Three volumes (1, 2 and 4 ml) of injection andtwo rates of injection (1 ml per 5 s and 1 ml per 10 s) werestudied. Small volumes (1 and 2 ml) of the more concentratedsolutions (1 % and 0.5%) produced predictable blockade withspread restricted to the lower thoracic segments. Increasingthe volume had little effect on the mean height of spinal blockade,but blockade was less predictable. Slowing the speed of injectionof the largest volume (4 ml) partly counteracted this effect.