The influence of hyperbaric bupivacaine temperature on the spread of spinal anesthesia

The distribution of spinal anesthesia is affected by the density and viscosity of the local anesthetic solution that, in turn, may be influenced by the temperature of the injectate. Our hypothesis in the present study was that the temperature of the injectate influences its distribution into the subarachnoid space. We measured the density and viscosity of hyperbaric 0.5% bupivacaine at 25 degrees C and 37 degrees C and tested the onset and extent of spinal anesthesia achieved by these solutions in 36 patients. The densities of the two solutions were similar (mean [SD]): 25 degrees C, 1.028 [0.000], versus 37 degrees C, 1.028 [0.000] (g/ mL), but the viscosity was more at 25 degrees C than at 37 degrees C (0.01116 [0.00003] versus 0.00843 [0.00002] g (.) cm(-1) (.) s(-1); P < 0.001). The maximum cephalad extent of loss of pinprick sensation was significantly higher with 37 degrees C (T2 with 37 degrees C versus T5 with 25 degrees C; P < 0.001), but the time to achieve peak block height was similar. In conclusion, we showed a consistent, but modest, increase in the cephalad level of spinal anesthesia by warming hyperbaric bupivacaine 0.5% from 25 degrees C to 37 degrees C. Viscosity was reduced in the warmed solution, but it is unclear if this or other factors led to the difference in spinal anesthetic level.