Using hypobaric local anesthetics, patients undergoing total hip replacement surgery (THR) can be anesthetized in the lateral decubitus position with operative side up, and do not need to be repositioned for operation. This can save preparation time and inadvertent change of anesthetic level due to position change. Number of studies have examined the use of hypobaric local anesthetics for THR, but the main focus of the studies was to compare the effect of various drugs or baricities, rather than adequate dosages. Therefore, we aimed to determine adequate dosages of hypobaric tetracaine for THR.

Sixty patients were randomly allocated into three groups. Spinal anesthesia was performed in the lateral decubitus position with the operated side uppermost using 0.2% tetracaine diluted with distilled water, 10, 12, or 14 mg was administered into the subarachnoid space.

Time to T10 block, the level of maximal sensory and motor block, and the incidence of hypotension were no different in the three dosage groups. The number of patients who showed adequate anesthesia (more than T10 and modified Bromage scale 2) were no different. Duration of sensory block and the time to complete motor recovery increased with dosage. The number of patients with less than a 2 hour sensory block was higher in the 10 mg group (50%) than in the two other groups (10% in 12 mg, 0% in 14 mg).

10 mg of hyperbaric tetracaine was not enough, and 14 mg adequate for a hip surgery of 2 hour duration. The two doses were similar in terms of the sensory and motor block level and the incidence of hypotension.