Extent of hyperbaric spinal anesthesia influences the duration of spinal block

Background: The influence of spread of spinal anesthesia on the duration of spinal blockade has been suggested but never investigated specifically. Because elimination of local anesthetic from subarachnoid space is probably dependent of the surface available for Its diffusion and vascular absorption, the current study was designed to evaluate the hypothesis that with a same dose of hyperbaric bupivacaine, a higher anesthetic level would result in a shorter duration of spinal blockade than a lower level. Methods: Three milliliters (15 mg) of hyperbaric bupivacaine, 0.5%, was injected intrathecally in 40 patients classified as American Society of Anesthesiologists physical status I or II scheduled for lower limb surgery during spinal anesthesia. To obtain significantly different anesthetic levels, the patients were positioned randomly either horizontally or with the torso elevated 30 degrees. Regression of sensory level and motor blockade, the appearance of pain at the operative site, and hemodynamic changes were evaluated. Results: The maximum cephalad spread of sensory blockade (expressed as the median with ranges in parentheses) was significantly higher in the horizontal group than in the group with 30-degree elevation of the torso, i.e., T3.5 (T1-T9) versus T10 (T6-L1), with respectively significantly faster regression times (mean +/- SD) by two segments (216 +/- 46 min vs. 253 +/- 64 min) and to segment L4 (269 +/- 53 min vs. 337 +/- 58 min), as well as shorter time to complete motor blockade recovery (173 +/- 34 min vs. 233 +/- 58 min) and faster appearance of pain at the operative site (221 +/- 68 min vs. 271 +/- 56 min). Conclusion: The results indicate that with the same dose of hyperbaric bupivacaine, the duration of spinal blockade is longer in patients with restricted spread.