Conus medullaris trauma: is there a greater risk in parturients?

Background: There is some evidence that anaesthetists often perform neuraxial blocks at a higher lumbar interspace than intended. It may be questioned whether parturients are at greater risk for neurological damage when the dura is perforated at a more cephalad interspace than L2-L3.

Methods: Thirty-six patients scheduled for elective Caesarean delivery under CSE anaesthesia were selected for study. Using a B-D Durasafe Adjustable needle combination, the skin-to-epidural distance and the width of the epidural space were measured and matched with 36 female patients undergoing the same anaesthetic technique for orthopaedic procedures.

Results: Pregnant patients had a higher bodyweight (77 vs. 67 kg, p = 0.007) than those scheduled for orthopaedic surgery. The skin-to-epidural distance was similar in both groups (5.3 vs. 5.1 cm, p = 0.3). The width of the epidural space was 1.1 mm larger in parturients (8.2 vs. 7.1 mm, p = 0.04). More patients in this group had tip-to-tip distances exceeding 10 mm (25 vs. 12%).

Conclusion: The greater epidural space or tip-to-tip distance between the epidural and spinal needle points in term parturients results in a lower margin of safety with respect to the distance from the dura to spinal cord or conus medullaris. Puncturing the correct interspace is, therefore, of crucial importance in pregnant patients.