INFLUENCE OF INJECTION SPEED ON THE SUBARACHNOID DISTRIBUTION OF ISOBARIC BUPIVACAINE 0.5-PERCENT

The purpose of this study was to compare the anesthetic characteristic s after two radically different speeds of intrathecal injection of iso baric 0.5% bupivacaine during continuous spinal anesthesia. Forty cons enting patients, undergoing hip surgery using continuous spinal anesth esia, were allocated randomly to two groups of 20 each according to th e rate of injection of 2 mL (10 mg) of isobaric 0.5% bupivacaine: FI ( fast injection = 2 mL during 2 to 3 s or approximately 0.75 mL/s) or S I (slow injection = 1 mL/min). No difference was observed between the two groups in terms of sensory and motor block or hemodynamic changes. However, the onset time to maximal sensory level was significantly sh orter in the SI group (16 +/- 9 min vs 24 +/- 6 min; P < 0.05). Those patients requiring reinjection entered the second part of the study (n = 23; 15 in the FI group and 8 in the SI group). Each of these remain ing patients was used as his or her own proper control. Those in the F I group received a slow reinjection and those in the SI group received a fast reinjection which consisted in all cases of 10 mg (2 mL) of is obaric 0.5% bupivacaine. When looking at the anesthetic characteristic s after reinjection, maximal sensory levels, as well as onset times, w ere very similar in both groups. At all times, the maximal sensory lev el obtained after reinjection was two dermatomes higher than after the initial injection. Duration of sensory block, which was calculated on ly in these 23 patients, was also comparable (126 +/- 44 min for FI an d slow reinjection group vs 146 +/- 25 min for SI and fast reinjection group). In conclusion, regardless of the speed of injection, there ar e no differences in anesthetic characteristics of spinal anesthesia us ing isobaric 0.5% bupivacaine.