BACKGROUND: When attempting a unilateral spinal anesthesia, many factors must be considered including patient's position, density and amount of the local anesthetics, needle design, injection speed. We evaluated a duration of lateral decubitus with low dose hyperbaric bupivacaine for maximizing the benefit.

METHODS: Hyperbaric 0.5% bupivacaine 6 mg was administered slowly through a 25-gauge Whitacre needle to 60 ASA 1-2 patients undergoing unilateral lower extremity surgery. The patients were randomly allocated to four groups based on the duration of lateral decubitus after spinal anesthesia: 5 minutes in Group I; 10 minutes in Group II; 15 minutes in Group III; 20 minutes in Group IV. Circulatory variables, sensory and motor block level were recorded.

RESULTS: The circulatory variables were stable in all patients. In the Group I, the success rate of unilateral motor block was significantly lower than other groups. In the Group IV, the success rate of unilateral sensory block was significantly higher than group I. In the Group II, III, IV, the patient's satisfaction scores were significantly higher than Group I.

CONCLUSIONS: When unilateral spinal anesthesia was attempted with 0.5% hyperbaric bupivacaine 6 mg, cardiovascular stability was achieved in the groups that patients are kept in a lateral decubitus for more than 5 minutes after spinal injection, and patient's higher satisfaction scores were achieved in the unilateral motor block and in the groups that patients are kept in a lateral decubitus for more than 15 minutes after spinal injection.