The effects of solution concentration and epinephrine on lateral distribution of hyperbaric tetracaine spinal anesthesia

In a search of a differential spinal block between dependent and nondependent sides, we investigated whether the use of a larger concentration of hyperbaric tetracaine (T) and/or the omission of epinephrine (E) would provide differential spread in patients left for 15 min in the lateral decubitus position. Spinal anesthesia was performed in the lateral decubitus position with the operated side dependent in 60 patients scheduled for lower limb surgery. All patients remained lateral for 15 min after spinal injection before being turned supine. They received 12 mg of T in 10% dextrose and E 0.2 mg was added when predicted duration of surgery was more than 90 min. The concentration of T to be used for each patient was randomized. This resulted in four groups of 15 patients: T 0.5% + E (control group), T 1% + E, T 0.5%, and T 1%. A unilateral anesthesia was defined as the presence of an adequate sensory (L-1 or higher) and/or motor (3 degrees) blockade on the dependent side and the absence of one or both modalities on the nondependent side, or as a duration of sensory (regression to L-2) and motor (1 degrees of recovery) blockade 20% longer on the dependent compared to the nondependent side. None of the 60 patients showed unilateral sensory block. A comparable number of patients in all groups showed unilateral motor block: four in T 0.5% + E, two in T 1% + E, four in T 0.5%, and five in T 1%. Likewise, a comparable number of patients in all groups showed a prolonged duration of sensory and motor block, respectively: six and eight in T 0.5% + E, six and nine in T 1% + E, six and eight in T 0.5%, and seven and seven in T 1%. In conclusion, although a preferential distribution of hyperbaric T toward the dependent side in patients of all four groups was noticed, the use of a larger concentration of T, omission of E, or combination of these two factors did not provide a more marked differential spread when compared to the standard solution of T 0.5% + E.