[Effect of injection speed on sensory blockade in spinal anesthesia with 0.5% hyperbaric tetracaine]

We investigation the effect of injection speed on sensory blockade in spinal anesthesia. Forty two female patients, scheduled for total abdominal hysterectomy, were allocated randomly to 3 groups of 14 each according to the injection speed of 0.5% hyperbaric tetracaine: Group F (fast; injection speed > or = 0.2 ml.s-1), Group M (moderate; 0.1 < injection speed < 0.2 ml.s-1) and Group S (slow; injection speed < or = 0.1 ml.s-1). Spinal puncture was performed via the median approach at the L3-4 interspace with the patient in a lateral position. The maximum level of sensory blockade was assessed by means of the pin-prick method in the midline 3, 5, 10, 20, 30, 60 minutes after injection. In Group F, the level of sensory blockade became higher quickly (within 5 min), but anesthetic effects were not so satisfactory. And, in this group, there were more patients with dyspnea than in other groups. We speculate that the turbulence made by fast injection in subarachnoid space caused unsatisfactory effects. In Group S, anesthetic level was becoming higher also 20 or 30 min after injection. The fixation of anesthetics requires about 30 min. In our opinion, anesthetics injected slowly were diluted less by CSF, and the actual baricity of them was higher, and this made the difference within 30 min. In Group M, anesthetic effects and patient's condition were stable. We suppose that this injection speed (0.1-0.2 ml.s-1) is suitable for spinal anesthesia.