Lumbar extradural injection pressures in pregnant women. An investigation of relationships between rate of infection, injection pressures and extent of analgesia.

Before the induction of labour in 34 pregnant women 1.5% lignocaine 10 ml was injected into the lumbar extradural space at constant rates between 0.143 and 0.333 ml s-1. Injection pressures and residual pressures were recorded and the extent of analgesia to pinprick was assessed. No significant correlation was found between the rate of injection and injection pressures or residual pressures over the range investigated. Analgesia was significantly more extensive on the side dependent during injections, but there was no significant correlation between the overall extent of analgesia and the rate of injection, injection pressures or residual pressures in the extradural space. It is concluded that there is no advantage from rapid extradural injections.