Effect of spinal flexion and extension in the lateral decubitus position on the unilaterality of spinal anesthesia using hyperbaric bupivacaine

Background and Aims: Many unilateral lower limb orthopedic surgeries are conducted under unilateral spinal anesthesia with full flexion of spine and immediate extension after local anesthetic administration into the subarachnoid space. Studies have shown that extension of the spine in lateral decubitous position makes cauda equina to sink to the dependent side due to gravity. Continuous flexion of the spine causes sunken cauda equina to be suspended in the middle of the subarachnoid space increasing the possibility of unilateralization of the block. Hence, this study was carried out to assess the effect of flexion and extension in lateral decubitus position in unilateral spinal anesthesia. Material and Methods: Sixty patients posted for elective unilateral lower limb below knee orthopedic surgeries were randomly allocated into two groups-group F (flexion of spine) and group E (extension of spine). Using a 25-gauge Quincke spinal needle, 8 mg of 0.5% hyperbaric bupivacaine was injected over a period of 80 s at L3-L4 interspace. Patients were kept in flexion or extension according to the group they belong to after drug administration. After 15 min of lateral position in either group, patients were turned to supine position. Sensory blockade was assessed by loss of pinprick sensation and motor blockade by modified Bromage scale. Results: Strict unilateral sensory block at 15th min was in 18 patients in flexion group compared with 11 patients in extension group which is statistically significant (p=0.03). At 60th min, there was no significant sensory unilaterality between the groups (p=0.06). A strict unilateral motor blockade at 15th min was also in 18 patients in group F and 11 patients in group E which was also statistically significant (p=0.04). At 60th min, seven patients in group F and three patients in group E had strict unilateral motor blockade which was also statistically significant (p=0.03). The maximum sensory level on the nondependent side was T10 in group F and T8 in group E, whereas it was T6 in both the groups on the dependent side. There was no difference in the two-segment regression of the sensory block, duration of sensory and motor blockade, the maximum level of the block, and hemodynamic status between the groups. Conclusion: Maintaining flexion of the spinal column for 15 min increases the likelihood of unilateral spinal block compared with extension of the spinal column during lateral decubitus positioning.