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
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
- Tube 1: Cell count and differential
- 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
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
References:
- EmDocs 2019. http://www.emdocs.net/unlocking-common-ed-procedures-the-impossible-space-lumbar-punctures/
- Taming the SRU 2018. http://www.tamingthesru.com/lumbar-puncture
- ALiEM 2016. https://www.aliem.com/pem-pearls-pediatric-lumbar-puncture-using-ultrasound/
- EM RAP 2016. https://www.youtube.com/watch?v=WpXGUn7eGZE
- https://litfl.com/csf-analysis/
- https://www.rch.org.au/clinicalguide/guideline_index/Lumbar_puncture/
Correct Positioning (shoulders/hips in-line)
Poor Positioning (right shoulder is forward causing rotation)