Comparison of differential blockade during spinal anesthesia using isobaric vs hyperbaric lidocaine 2%

Purpose: To compare the extent of the sensory, motor and sympathetic block produced by a single dose of 60 mg lidocaine at the same concentration (2%) and volume but at different baricity injected intraspinally. Method: In a randomised double blind study, 40 ASA I - II patients were sch eduled for elective surgery (orthopedic, urologic, peripheral vascular and lower digestive procedure), They were divided in two groups. Twenty patient s received 60 mg lidocaine 2% in a hyperbaric solution and 20 received 60 m g lidocaine 2% in a isobaric solution. The levels of sensory (pinprick, ice ) motor (Bromage scale) and sympathetic blockade (galvanometry, cutaneous b lood flow, temperature) were measured at 0, 5, 10, 15, 20 and 30 min. Results: There were no differences between the groups with regard to maxima l height of sympathetic block, sensory level to pinprick: T-5 +/- 2.4 for i sobaric group, T-6 +/- 3.6 for hyperbaric group or to cold: T-3 +/- 2.3 for isobaric group, T-4 +/- 2.7 for hyperbaric group. Hyperbaric lidocaine 2% produced a more pronounced sensory (pinprick, ice) and motor block on the d ependant than on the non-dependant side. Conclusion: The baricity of 60 mg lidocaine injected intraspinally in the l ateral decubitus position did not influence the cephalad spread of sensory or sympathethic blockade. In the hyperbaric group, the dependent side showe d a more pronounced sensory (pinprick, ice), and motor block.