Spinal Anesthesia With Tetracaine in 0.75% Glucose: Influence of the Vertebral Interspace Used for Injection

Background and ObjectivesThe anesthetic behavior and hemodynamic consequences of spinal anesthesia with marginally hyperbaric tetracaine containing a low concentration of glucose injected at two different interspaces were examined and compared with those of conventionally hyperbaric solution.MethodsOne-hundred twenty ASA Physical Status I or II patients scheduled for elective surgery to the lower limb were sequentially assigned to one of three equal groups to receive spinal anesthesia: Group 1 received 0.5% tetracaine in 0.75% glucose with 0.125% phenylephrine at the L2-L3 interspace; group 2 0.5% tetracaine in 0.75% glucose with 0.125% phenylephrine at the L3-L4 interspace; group 3 0.5% tetracaine in 7.5% glucose with 0.125% phenylephrine at the L3-L4 interspace. Neural block was assessed in a double-blinded manner by cold, pinprick, and touch sensation, and a modified Bromage scale after the injection of the study drug.ResultsInjection at the L2-L3 interspace produced significantly higher spread of analgesia [median T7 (10th, 90th percentiles T10, T4)] than injection at L3-L4 interspace [T10 (L1, T5)] when using the solution in 0.75% glucose. There were no significant differences in peak dermatomal levels between groups 1 and 3, but the number of patients who required ephedrine for the treatment of hypotension was larger in group 3.ConclusionsA marginally hyperbaric tetracaine solution injected at the L2-L3 interspace with the patient in the lateral position produced greater extent of cephalad spread than that at the L3-L4 interspace. When compared to a conventionally hyperbaric tetracaine solution injected at the L3-L4 interspace, the marginally hyperbaric solution injected at the L2-L3 interspace caused less hemodynamic variability despite similar levels of maximum sensory block.