Lumbar Puncture (LP)

Lumbar Puncture (LP)

Indications:

1. Diagnostic aid (infection, hemorrhage, leptomeningeal carcinomatosis, multiple sclerosis, Guillain-Barre Syndrome, inflammatory conditions, to test for therapeutic response in NPH, normal pressure hydrocephalus, before shunting)

2. Therapy for idiopathic intracranial hypertension

3. Infusion of anaesthetic (“spinal”), chemotherapy, or contrast agents (myelography)

Contraindications

- INR > 1.4 or other coagulopathy

- platelets < 50

- infection at desired puncture site

- obstructive / non-communicating hydrocephalus

- intracranial mass

- high intracranial pressure (ICP) / papilledema (relative contraindication, depends on etiology, especially with intracranial mass lesion secondary to the increased risk of transtentorial or cerebellar herniation)

- focal neurological symptoms/signs, decreased level of consciousness (LOC) (see CT before LP section below)

- partial / complete spinal block

- acute spinal trauma

Complications:

Relatively common

1) Post LP headache (rates vary from 1-70%, probably <5% for persistent troublesome headache, “low pressure headache” i.e. headache increases when upright and diminishes when supine, occasionally associated with nausea, vomiting and tinnitus, onset within 1-3 days and usually lasts <5d)

2) Post LP back pain (<1/3 of patients, due to local soft tissue trauma)

Rare

3) Infection e.g. spinal abcess, meningitis (estimated at 0.2%)

4) Spinal subdural / epidural hematoma (predominantly in patients with a coagulopathy)

5) Nerve root or spinal cord injury (transient nerve root irritation much more common than persistent injury)

6) Epidermoid tumor implantation (very low risk if needle advanced only with stylet in place)

7) Transtentorial or cerebellar herniation (risk 0-5% in patients known to have an intracranial mass and high ICP)

8) Complications secondary to low intracranial pressure

a) Hearing loss, CN VI paresis

b) Intracranial subdural hygroma / hematoma

10) Complete spinal block (in patients with partial spinal block)

11) Pachymeningeal enhancement may be seen on gadolinium-enhanced MRI of head or spine after a lumbar puncture (may be related to low pressure)

CT scanning of the head before LP in suspected meningitis:

- The most worrisome contraindication to lumbar puncture is the suspicion of increased ICP due to a cerebral mass lesion. Performing a lumbar puncture in these patients may lead to either trans-tentorial or uncal herniation and acute neurological deterioration.

- The absence of all these features makes a significant lesion precluding LP very unlikely:

1) Age > 60 yrs

2) Immuno-compromised state

3) History of CNS disease (eg. grand mal seizures, brain tumour, hydrocephalus, multiple sclerosis)

4) Seizure within one week of presentation

5) Abnormal LOC

6) Unable to answer two questions correctly or follow two commands

7) Abnormal neurological examination (visual field defect, facial palsy, pronator drift, aphasia)

eg. An LP may safely be performed without first doing a CT head in a young previously healthy patient with no history of seizures, a normal level of consciousness and a normal neurological exam.

Anatomy (Click here to see figure)

- Spinal cord usually terminates at L1 or L1/L2 in adults (~95% of adults)

- Thecal sac terminates at ~S2

- Intercristal line is an imaginary line that connects the superior border of the iliac crests

- L4/5 interspace is the first interspace caudal to the intercristal line

Materials

- sterile gloves and mask
- LP kit (contains: syringe, 25 and 22G needles, 1% lidocaine, sterile drapes, sponges and gauze, 22G LP needle, stopcock and manometer, 4 collection tubes and band-aid)

- sterilization solution (chlorhexidine or proviodine)
- extra spinal needle, 20 or 22-gauge
- extra sterile sponges – 2x2s or 4x4s

*** If collecting for cytology, get appropriate container with cytofixative ready beforehand

Technique

1. Obtain patient consent. Describe reason for procedure, procedure itself and potential complications.

2. Position the patient. There are 2 recommended positions:

a. Lateral decubitus (Click here to see figure)

- Place patient in lateral decubitus position (right or left)

- Lumbosacral area should be as close to edge of bed as possible

- Pillow under head and between legs

- Head flexed and legs curled up towards chest (“fetal” position)

- Shoulders and hips must be perpendicular to bed / floor

b. Sitting up

- patient sits up and leans over a table, resting head and arms on a pillow

- the back of the patient’s legs should be resting against the edge of the bed

- torso / spinal column should be perpendicular to the bed / floor

- ask patient to bulge out lumbosacral spine

3. Landmark. Identify intercristal line and the L4/L5 interspace. Mark this interspace by making an impression on the patient’s skin with the tip of a pen.

4. Carefully open LP kit and put cleaning solution in reservoir.

5. Put on mask and sterile gloves.

6. Sterilize the field using the sterilizing solution and sponges provided. Clean a 6 inch area around the desired entry site, proceeding outward in concentric circles. Do this 3 separate times. Place sterile drape over the field.

7. Ensure all items in LP tray are ready for use. Eg. 1% or 2% lidocaine loaded into syringe, collection tubes open, test to see that the stylet slides in/out of LP needle easily, stopcock and manometer for opening pressure measurement ready.

8. Local anaesthesia. Using a 25G needle, inject 1% or 2% lidocaine under the skin at the desired entry site. A small bleb under the skin is sufficient. Switch the needle tip to the 22G needle and anaesthetize deeper structures by inserting the needle further, injecting lidocaine while proceeding forward.

9. Insert LP needle. The bevel should be parallel to the spinal column. Always advance the needle with the stylet in place. Aim needle in the midline, slightly cephalad, towards the patient’s umbilicus. Advance needle slowly until it is inserted 2-3 cm, then withdraw the stylet to check for CSF return. Continue to advance the needle, periodically checking for CSF return. Often a "pop'' is appreciated as the needle pierces the dural membrane. If the needle meets bone or if blood returns (hitting the venous plexus anterior or posterior to the spinal canal), withdraw the needle to the skin and redirect the needle.

10. Once CSF flow is obtained, measure the opening pressure by attaching first the stopcock to the LP needle and then the manometer to the stopcock. CSF pressure measured in this way is only accurate with patient in lateral decubitus position and relaxed (ie. Neck not flexed, legs extended, no valsalva).

11. Collect CSF fluid into sequential tubes. 1-2 ml in each tube is sufficient for basic investigations. More fluid will need to be collected for special tests e.g. viral PCR, cytology etc. (see below)

12. Reinsert stylet. Withdraw needle. Place band-aid over insertion site.

Tips

1. Position, position, position

2. Try one level above or below (adults)

3. Try 20G needle

4. Ask someone else to try

5. If you can’t get it….abort and order LP under fluoroscopy

Post-LP mobilization and dural puncture headache

- A period of bed rest along with supplementary fluids has traditionally been recommended post-LP to decrease the risk of post-dural puncture headache

- There is no good evidence that either of these recommendations alters the risk of post-dural puncture headache

What to order

The basics

Tube #1 Cell count and differential

Tube #2 Chemistry (protein, glucose)

Tube #3 Culture and Gram stain

Tube #4 Cell count and differential

Other tests to consider

- Will need to collect extra fluid for these tests in tube #3 or #4.

India ink and / or Cryptococcal Ag (for Cryptococcus neoformans)

AFB and / or PCR for TB

Viral PCR (includes HSV, CMV, EBV)

arbovirus / WNV, echovirus

VDRL

fungal culture

viral culture

PCR and /or antibody titers for Lyme ds.

oligoclonal banding (3-4 ml)

IgG index, IgG :albumin ratio

cytology (must be collected in cytology fixative) (8-10ml)

flow cytometry (3-4 ml) (NOT in fixative)

How much CSF to withdraw?

- CSF is produced at a rate of 0.3 ml/min in adults or 450 ml/24h

- CSF volume is approximately 150 ml in an adult

- For basic investigations, only require 4-8 ml

- May require more volume for special tests (see above). Maximum to be removed at one time should probably not exceed 20 ml.

- 20-30 ml can be removed in case of NPH “tap test” to gauge response.

Normal values

- Opening pressure: 5-20 cm water (only valid in lateral decubitus position)

- Appearance: clear, colorless

- Nucleated cells: <5 per ml

- RBC: <5 per ml

- WBC:RBC ratio: 1:700 (ie. For every additional 700 RBCs seen due to presumed traumatic tap, one WBC is expected)

- Glucose: 2/3 serum value

- Protein: 200-450 mg/L

CSF Findings

Click here to view Table (not yet available, in preparation)

Traumatic tap (TT) vs. SAH?

- Supernatant: Clear in TT. In SAH, expect to see xanthochromia (yellowish discolouration). NOTE: Xanthocromia takes time to develop ie. Seen in 70% by 6h, 90% by 12h after SAH.

- RBC count: Declines as CSF drains in TT, therefore compare tube #1 to tube #4. Does not decline in SAH

- WBC:RBC ratio: Similar to peripheral blood in TT (i.e. 1:700). SAH usually promotes a leukocytosis.

- Clotting of fluid: May clot in TT if RBC count high. Usually does not clot in SAH, since there are no clotting factors in CSF.

- Protein: In TT, increase of approx. 1 mg per 100 RBC. Levels are greater than this in SAH.

- Opening pressure: Usually normal in TT and usually elevated in SAH.

- Repeat LP: Usually clear in TT and still bloody / xanthochromic in SAH (CSF taken at a different spinal level)

DDx of CSF hypoglycaemia

Infectious - Bacterial meningitis, TB, Fungal, Cysticercosis, Amoebic, Syphilis, Trichinosis, Mumps (25%), HSV, VZV

Inflammatory - Sarcoidosis

Neoplastic - LM carcinomatosis

Vascular - SAH (4-8 days post-bleed)

Metabolic -Hypoglycemia

References:

Hasbun R, Abrahams J, et al. Computed tomography of the head before lumbar puncture in adults with suspected meningitis. N Engl J Med 2001; 345: 1727-33.

Sudlow C, Warlow C. Posture and fluids for preventing post-dural puncture headache (Cochrane Review). In: The Cochrane Library, Issue 2, 2003. Oxford: Update Software.

Handbook of Neurosurgery. Greenberg. Thieme Medical Publishers. 2001

Merritt’s Textbook of Neurology. 10^th ed. Rowland. Williams and Wilkins.

Last update: 2003-05-12

Reviewed by: pending review

Neurological Medicine Pocketbook

http://www.uwo.ca/cns/resident

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