Lumbar Puncture

Most Common "Emergency Room" Indications

  • Analyse CSF
    • r/o infectious (bacterial, viral, fungal)
    • r/o blood or xanthochromia (subarachnoid hemorrhage unable to rule out with CT [eg. symptom onset >6h])
  • Other
    • Measure/reduce CSF pressure in idiopathic intracranial hypertension
    • May be helpful to diagnose multiple sclerosis or Guillain Barre syndrome


  • Infection at site of puncture (eg. overlying cellulitis, abscess)
  • Severe risk of bleeding (eg. plat<20, INR>1.5, coagulation disorder, anticoagulation)
  • Trauma at site
  • Increased ICP causing risk of herniation (see indications for CT head before LP)

Indications for CT head before LP (r/o increased ICP)

  • Immunocompromised
  • History of previous CNS disease (eg. mass, CVA)
  • History of seizure within 1 week of presentation
  • Presence of neurologic deficit on exam (arm/leg drift, aphasia, gaze palsy, facial palsy, papilledema)
  • Altered mental status

Note: If suspect increased ICP, do not wait for CT scan to confirm, treat aggressively (head elevation, hyperventilation, mannitol or hypertonic saline IV, etc...)

CT findings that prohibit LP

  • Midline shift
  • Obstructive hydrocephalus
  • Basilar cisterns compressed
  • Posterior fossa mass


  • Post-LP headache (30%)
    • Onset up to 14d (most within 3d)
    • Pressure-like frontal/temporal headache, postural improves supine
    • Treatment
      • Fluids, Acetaminophen, NSAIDs, antiemetics, caffeine (can give 500mg in 1L NS over 1 hour)
      • If persistent and severe, may consider epidural blood patch
  • Infection/Bleeding (rare)
  • Cerebral herniation (in increased ICP)



  • In adults, spinal cord ends (conus medullaris) between L1-L2
  • In pediatric patients, may be as low as L3 at birth
  • Aim between L3-L4 and L4-L5, or L4-5 in pediatrics
    • Iliac crests at level of L4 in adults, L5 in pediatrics
    • Iliac crests can pointas high as L1-L2 in women and obese patients
  • Consider using ultrasound to identify conus medullaris (end of spinal cord), and depth of insertion
    • Scan longitudinal
    • Identify conus medullaris
    • Identify and mark superior and inferior borders of intervertebral space of interest
    • Measure distance from skin to dura (for depth of insertion)
      • In adults, approximate insertion is 45-55mm but variable especially if obese (consider ultrasound to measure)
      • In children, this is approximately 0.03 x height (cm)
    • In transverse view mark midline and intervertebral space of interest


  • Lateral recumbent (with knees tucked to chest, holding pillow +/- assistant)
    • Ensure shoulders and hips are in line with one another (avoid rotational positioning of the spine)
    • Ask to slouch rather than bend from hips
    • Avoid over flexing neck in infants (can caus respiratory compromise)
  • Seated position (helpful in large habitus)
    • Cannot measure opening pressure


  • Topical anesthetic if pediatrics +/- oral sucrose
  • Clean large site with chlorhexidine or betadine
  • Don PPE with sterile gloves, procedure mask, cap
  • Set-up items in a sterile field
    • Place sterile drape
    • Open collecting tubes in numerical order
    • Prepare manometer (connect pieces to three way valve at vertical position, knob on valve points to port that is off)
  • Know estimated insertion distance from skin to dura (see landmark section above)


  • Local anesthesia with 1-2% lidocaine using smallest needle (eg 25G) both superficial skin and intended path of LP needle
  • Use spinal needle 22G or 25G (atraumatic/blunt or smallest if available) with bevel facing parallel to ligament fibers (upwards if patient lateral decubitus),
    • Directing needle midline toward umbulicus (usually this is angled cephalad)
    • Ensure needle perpendicular to back


    • If hit resistance (possibly spinous process)
      • Recheck patient positioning, ensure midline at correct level
      • Back up to skin surface and direct more cranially (or caudally)
    • If no resistance and no fluid at estimated depth
      • Recheck patient positioning, ensure midline at correct level
      • Consider longer needle
    • If severe pain down right/left leg
      • Recheck patient positioning, ensure midline at correct level
      • Back up to skin surface and direct more left (if right leg pain) or right (if left leg pain)


  • Once into the space (eg. felt a pop, or measured distance prior with ultrasound), remove stylet and collect CSF
    • Ask patient to slowly extend (straighten) legs to allow free flow of CSF
    • May obtain opening pressure (if patient in lateral recumbent position)
      • Normal pressure for adults is in the range of 7-18 cmH2O
    • Deep breaths may facilitate CSF flow
    • Each tube requires 1mL (5-10 drops)
      • Tube 1: Cell count and differential
        • If bloody can use it for culture first
      • Tube 2: Gram stain, bacterial and viral cultures
      • Tube 3: Glucose, protein, protein electrophoresis (if indicated)
      • Tube 4: Second cell count and differential (if indicated) or hold tube for special tests or additional cultures (may add 5mL)
        • Up to 40mL of CSF can safely be removed
    • Once CSF collected, reinsert stylet, remove needle, and place dressing
  • Apply usual occlusive dressing (Tegaderm or band-aid)
  • Some may consider instructing patient to lie supine (up to an hour) post-LP to decrease post-procedural headache (but no evidence for post-LP headache)


Corrections for bloody tap

  • WBC correction (if peripheral WBC and RBC counts are within normal limits):
    • Subtract 1 WBC for every 750 RBC in CSF
  • Protein correction
    • For each 1000 RBC decrease protein value by 1mg/dl

Delay in LP

  • CSF cultures are negative 2h after parenteral antibiotics in meningococcal meningitis, and 6h in pneumococcal meningitis

Correct Positioning (shoulders/hips in-line)

Poor Positioning (right shoulder is forward causing rotation)