A comparative study on position and paramedian neuraxial access on healthy volunteers using three-dimensional models registered to lumbar spine ultrasound.

PURPOSE: Optimizing patient position and needle puncture site are important factors for successful neuraxial anesthesia. Two paramedian approaches are commonly utilized and we sought to determine whether variations of the seated position would increase the chance of puncture success.

METHODS: We simulated paramedian needle passes on three-dimensional lumbar spine models registered to volumetric ultrasound data acquired from ten healthy volunteers in three different positions: 1) prone; 2) seated with thoracic and lumbar flexion; and 3) seated as in position 2, but with a 10° dorsal tilt. Simulated paramedian needle passes from the right side performed on validated models were used to determine L2-3 and L3-4 neuraxial target size and success. We selected two paramedian puncture sites according to standard anesthesia textbook descriptions: 10 mm lateral and 10 mm caudal from inferior edge of the superior spinous process as described by Miller, and 10 mm lateral from the superior edge of the inferior spinous process as described by Barash.

RESULTS: A significant increase in the area available for dural puncture was found in the L2-3 (61-62 mm2 ) and L3-4 (76-79 mm2 ) vertebral levels for all seated positions relative to the prone position (P < 0.001). Similarly, a significant increase in the total number of successful punctures was found in the L2-3 (77-79) and L3-4 (119-120) vertebral levels for all seated positions relative to the prone position (P < 0.001). No differences were found between seated positions. The Barash puncture site achieved a higher number of successful punctures than the Miller puncture site in both the L2-3 (19) and L3-4 (84) vertebral levels (P < 0.001).

CONCLUSION: An added dorsal table tilt did not increase puncture success in the seated position. The landmarks for puncture site described by Barash resulted in significantly more successful punctures compared with those described by Miller in all positions.