•Indication: To diagnose meningitis vs. demyelinating disease, to confirm SAH, to relieve intracranial hypertension

•Contraindications: any signs of elevated ICP

•Equipment: lidocaine, 18-22G spinal needle and stylet with attached 3ml syringe, sterile towels, betadine

•Technique: Position pt in either lateral decubitus or sitting position, then locate site for puncture by palpating iliac crests b/l and imagining a line connecting the two (L4).  Prep pts back w/ betadine, then drape pt.  Palpate for L4 interspace, infiltrate lidocaine into skin,  and gradually insert needle in the midline.  Two ‘pops’ should be felt, the 1st representing penetration of the ligamentum flavum, and the 2nd upon entering the subarachnoid space.  Remove stylet and collect CSF.

•Complications: bleeding, infection, headache, herniation