Influence of the baricity of a local anaesthetic agent on sedation with propofol during spinal anaesthesia

Background: This study examined the effect of different levels of spinalanaesthesia, induced by solutions of different baricity butcontaining the same amount of local anaesthetic agent, on therequirement for sedation with propofol. Methods: Thirty-six patients undergoing varicose vein surgery under spinalanaesthesia were randomly allocated to receive tetracaine 15mg in 3 ml of either glucose 5% (hyperbaric) or CSF (isobaric).I.V. propofol was started 5 min after the intrathecal injectionand was titrated to maintain a bispectral index (BIS) scoreof 65–75. The propofol requirements to maintain this rangein the two groups were compared every 5 min. Results: The propofol requirement was always lower in the hyperbaricgroup, with the differences becoming statistically significant20 min after the intrathecal injection. Total consumption ofpropofol over the 55 min of the study was also less in the hyperbaricgroup. Conclusion: The known difference in level of spinal anaesthetic block inducedby solutions of different baricity, but the same dose of localanaesthetic, was associated with different requirements forpropofol sedation as determined by BIS assessment.