Effect of speed of injection on the maximum sensory level for spinal anesthesia using plain bupivacaine 0.5% at room temperature.
BACKGROUND AND OBJECTIVES: The aim of this study was to investigate if a ten-fold difference in speed of injection of a plain solution of bupivacaine 0.5% at room temperature into the subarachnoid space would result in a temperature-dependent change in baricity large enough to be reflected in a significant difference between the maximum levels of sensory blockade. METHODS: In this prospective study, 40 male patients were randomly assigned to one of two groups. Group 1 patients received 3 ml plain bupivacaine 0.5% (20-22 degrees C) with the speed of injection as fast as possible. Group 2 patients received 3 ml plain bupivacaine 0.5% (20-22 degrees C) at a rate of 0.05 ml/sec. Thirty minutes after subarachnoid injection the maximum level of sensory blockade was determined by pinprick in the anterior axillary line by a blinded observer. RESULTS: The mean maximum level of sensory blockade in patients of group 1 was T7.5 (median, T7; range, T3-12) and in group 2 patients T6.4 (median, 5.5; range, T3-11), the difference not being statistically significant (p > 0.05). CONCLUSIONS: There is no clinically relevant influence on the maximum level of sensory blockade when bupivacaine 0.5% at room temperature is injected with a ten-fold difference in speed.