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

Contraindications

• 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

Complications

• 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)

Procedure

Landmark

• 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

Position

• 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

Prepare

• 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)

Procedure

• 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

Trouble-shooting

• 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)

Success!

• 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)

Interpretation

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