None of the EDs I have worked in recently require us to perform lumbar punctures, but it is one of our competencies - so we should be able to do it...and could be tested on it!
1. Palpate the iliac crests and draw an imaginary line between the two. Mark this space (L3/L4) or the one below (L4/5) with a gentle indentation. Ask the patient if it feels like this is in the dead centre.
Remember the spinal cord ends at L1/2 in adults.
2. Surgically scrub.
3. Clean the skin with antiseptic. If you're using a gallipot, remove the chlorhexidine after washing so there is no chance of accidentally injecting it. We should be using 0.5% chlorhexidine - it is better at preventing infection than iodine, and is less neurotoxic than 2%.
4. Infiltrate local anaesthesia into the space
5. Insert a 20 or 22 gauge spinal needle into the space, with the stylet.
You will pierce the skin, supraspinous ligament, the interspinous ligament, and then feel a slight resistance as you go through the ligamentum flavum. The needle then goes through the dura with a pop, and through the arachnoid into the sub arachoid space.
6. Angle the needle slightly caudally, with the bevel parallel to the flanks so it pushes, rather than tears the dura.
7. Check opening pressure if needed.
8. Collect CSF - get the patient to extend legs to speed up flow if needed.
9. Replace the stylet before removing the needle to reduce pressure.
10. Encourage ambulation.
Minor neurologic symptoms such as radicular pain or numbness
Late onset of epidermoid tumors of the thecal sac
Possible raised intracranial pressure (headache, blurred vision, reduced GCS, vomiting, papilloedema)
Thrombocytopenia or other bleeding diathesis (including ongoing anticoagulant therapy)
Suspected spinal epidural abscess, cellulitis overlying the area