Figure 6: Anatomy of the spinal cord, epidural space and the subarachnoid space.
The patient should be sitting or lying on their side. Back flexion opens the intervertebral spaces. The back is cleaned using standard antiseptic solution. The anaesthetist should adopt an aseptic technique. Aim to identify the L3/4, L4/5 or L5/S1 interspace (use Tuffier’s line). The chosen interspace is infiltrated with local anaesthetic. The spinal needle is inserted in the midline, aiming slightly cranially. Resistance increases as the ligamentum flavum is entered and when the dura is encountered, with a sudden "give" as the dura is pierced. Correct placement of the needle is confirmed by cerebrospinal fluid at the hub.