Comparison of glucose 7.5% and 0.75% with or without phenylephrine for tetracaine spinal anaesthesia

To investigate whether a marginally hyperbaric tetracaine solution with or without phenylephrine could produce consistent blocks as compared with a conventionally hyperbaric tetracaine solution injected at L3-4 interspace with the patient in the lateral position. We studied 120 ASA I or II patients scheduled for elective surgery to the lower limb. Patients were randomly divided into four equal groups to receive spinal anaesthesia using tetracaine 0.5% in glucose 0.75% or 7.5%, with or without phenylephrine 0.125%. Neural block was assessed in a double-blind manner by cold, pinprick, and touch sensation, and a modified Bromage scale after the injection of the study drug. The median (10th, 90th percentiles) peak dermatomal level to pinprick obtained by the solutions in glucose 0.75% was T10 (L1, T5), which was lower than that obtained by the solution in glucose 7.5% extending to T5 (T10, T3) and T5 (T10, T2) with or without phenylephrine, respectively (P < 0.0001). The addition of phenylephrine prolonged the time to two-segment regression but did not change the maximum extent of blocks. A marginally hyperbaric tetracaine with or without phenylephrine produced consistent blocks with spread restricted to the lower thoracic segments when administered intrathecally at the L3-4 interspace with the patient in the lateral position.