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 scheduled for elective surgery (orthopedic, urologic, peripheral vascular and lower digestive procedure). They were divided in two groups. Twenty patients received 60 mg lidocaine 2% in a hyperbaric solution and 20 received 60 mg lidocaine 2% in a isobaric solution. The levels of sensory (pinprick, ice) motor (Bromage scale) and sympathetic blockade (galvanometry, cutaneous blood flow, temperature) were measured at 0, 5, 10, 15, 20 and 30 min. RESULTS: There were no differences between the groups with regard to maximal height of sympathetic block, sensory level to pinprick: T5 +/-2.4 for isobaric group, T6 +/-3.6 for hyperbaric group or to cold: T3 +/-2.3 for isobaric group, T4 +/-2.7 for hyperbaric group. Hyperbaric lidocaine 2% produced a more pronounced sensory (pinprick, ice) and motor block on the dependant than on the non-dependant side. CONCLUSION: The baricity of 60 mg lidocaine injected intraspinally in the lateral decubitus position did not influence the cephalad spread of sensory or sympathethic blockade. In the hyperbaric group, the dependent side showed a more pronounced sensory (pinprick, ice), and motor block.