Mechanism of extension of spinal anaesthesia by extradural injection of local anaesthetic

Abstract

We have examined the effect of extradural injection of 0.5% bupivacaine or normal saline on the progression of spinal anaesthesia in 28 patients undergoing Caesarean section. Three groups were studied. Subarachnoid anaesthesia was established in all patients. Group A (n = 10), the control, received no extradural injection for 20 min. Group B (u= 9) received extradural bupivacaine 10 ml and group C (n = 9) received extradural saline 10 ml 5 min after the subarachnoid injection. Sensory levels were compared at 5-min intervals and extension of the block was found to be similar in groups B and C and significantly faster than the control (P < 0.05). The quality of anaesthesia and incidence of adverse effects was similar for all three groups. We conclude that the mechanism of extension of spinal anaesthesia by extradural injection of local anaesthesia is largely a volume effect. (Br. J. Anaesth. 1992; 69: 457-460). © 1992 British Journal of Anaesthesia.