Hypobaric spinal anesthesia with 0.2% tetracaine for total joint hip arthroplasy.

Purpose: Hypobaric local anesthetics for total hip replacement (THR) have potential advantages related to body position and differential block. However, the dose requirements of hypobaric local anesthetics for THR have not been clearly established. Therefore, we undertook a dose-response study of hypobaric tetracaine for THR.

Methods: In a randomized, controlled, and double-blinded manner, three groups of 20 patients each undergoing THR received spinal anesthesia using either 10, 12, or 14 mg of 0.2% hypobaric tetracaine in a lateral decubitus position, with the operated side up. Adequate anesthesia was defined as: 1) upper sensory block between T10 and T4; 2) motor block of modified Bromage scale 2 or 3; and 3) time to sensory remission to the L2 level of more than three hours.

Results: The number of patients who achieved adequate sensory and motor block levels was similar amongst the three groups. However, all patients who received 14 mg had a sensory remission time to L2 of more than three hours while only 30% of the patients in the 12 mg group and no patient in the 10 mg group had the same remission time. A significant differential block was observed between the non-dependent and the dependent sides, but the degree of differential block was not different between the groups.

Conclusion: 10 to 14 mg of 0.2% hypobaric tetracaine achieved similar and adequate block levels, but different regression times. To ensure complete sensory block duration for THR, we recommend using 14 mg of 0.2% hypobaric tetracaine.