A Comparison of Bupivacaine and Tetracaine in Spinal Anaesthesia with Special Reference to Motor Block

Abstract

Patients (36) received spinal anesthesia with either glucose-free bupivacaine (22.5 mg) or glucose-containing solutions of bupivacaine (20 mg) or tetracaine (15 mg). The duration of analgesia in the lower thoracic and lumbar segments was significantly longer with glucose-free bupivacaine than with the other solutions. Using a quantitative method for measuring muscle strength, the motor block was recorded for 3 types of movements: hip flexion, knee extension and plantar flexion of the big toe. Movements of the lower part of the thoracic cage were recorded at the same time. The length of time from spinal injection to complete motor block was short and without notable difference between all 3 groups. Regression of the motor block tended to start earlier for hip flexion and knee extension than for plantar flexion of the big toe. For all 3 movements the regression of the motor block began significantly later in the glucose-free bupivacaine group than in the other groups. During the regression phase, muscle strength returned significantly later in the glucose-free bupivacaine group than in the bupivacaine group containing glucose, and knee extension returned significantly later in the glucose-free bupivacaine group than in the tetracaine group. No difference in motor block was found between the hyperbaric solutions of bupivacaine and tetracaine. For hip flexion (L1-L3), there was no noteworthy difference between the level of analgesia and the motor block segments, whereas for plantar flexion of the big toe (L5-S2) the level of analgesia lay 2-3 segments higher than the motor block segments. In 7 patients, during spinal anesthesia there was a reduction in respiratory deflections corresponding to the lower thorax. As the Bromage scale only represented the motor block during the first 1/2 of the regression phase, it was of limited value. As measured according to the Bromage scale, the patients could not be mobilized until 1-2 h after complete restoration of the muscle strength.