Landmark Guided Midline Versus Pre-procedural Ultrasound Guided Paramedian at L5S1 for Spinal Anaesthesia

Spinal anesthesia is widely performed using a surface landmark based 'blind' technique. Multiple passes and attempts while administering spinal anesthesia are associated with a greater incidence of post dural-puncture headache, paraesthesia and spinal hematoma.

Real time and pre-procedural neuraxial ultrasound techniques have been used to improve the success rate of spinal anesthesia. The use of real time ultrasound-guided spinal anesthesia has to date been limited to case series and case reports.Its use may be limited by the requirement for wide bore needles and the technical difficulties associated with simultaneous ultrasound scanning and needle advancement. The use of pre-procedural ultrasound has been shown to increase the first pass success rate for spinal anesthesia only in patients with difficult surface anatomic landmarks. No technique has been shown to improve the success rate of dural puncture when applied routinely to all patients. Routine use of pre-procedure ultrasound guided paramedian approach results in 50% reduction in number of passes required for spinal anaesthetic, from a study at Cork University Hospital (awaiting publication). L5-S1 is the widest interlaminar space and provides minimal contribution to overall movement of lumbar spine.This interspinous space might still be accessible even if the patient has minimal spine flexion. We also noted that spinal needle insertion via the L5-S1 interspace was associated with the fewest passes in the pre-procedure guided ultrasound group (although non-significant).

We hypothesise that the routine use of pre-procedural ultrasound-guided paramedian spinal technique at L5S1 interspinous space will result in fewer needle passes to enter the subarachnoid space when compared to the conventional landmark based midline approach.