Lumbar Puncture

Question 1

Normal range CSF opening pressure?

Answer 1

Normal range CSF opening pressure 10-18cm H2O.

Question 2

Prior to performing lumbar puncture in patients presenting with focal neurology or raised ICP what should be done?

Answer 2

Neurological imaging

Question 3

Clinical indications for lumbar puncture and CSF analysis?

Answer 3

1. Suspected subarachnoid haemorrhage
2. Suspected meningitis/encephalitis
3. Immunological disorders such as multiple sclerosis or Guillain-Barr é Syndrome

Question 4

CSF analysis: Bacterial meningitis

Answer 4

Appearance: Clear, cloudy, or purulent
Opening pressure: Usually elevated (>25 cmCSF)
WBC count: >100 cells/µL
>90% PMN
Partially treated cases may have as low as 1 WBC/µL
Glucose level: Low (< 40% of serum glucose)
Protein level: Elevated (>50 mg/dL)
Additional tests: CSF Gram stain and cultures, blood cultures, CSF bacterial antigens, CSF polymerase chain reaction (PCR) for common viruses

Question 5

CSF analysis: viral meningitis

Answer 5

Appearance: Clear
Opening pressure: Normal or elevated
WBC count: 10-1000 cells/µL
Classically lymphocytes but may be PMN early
Glucose level: >60% serum glucose (may be low in HSV infection)
Protein level: Elevated (>50 mg/dL)
Consider additional tests: CSF Gram stain and cultures, blood cultures, CSF bacterial antigens, CSF PCR for herpes simplex virus (HSV), varicella-zoster virus (VZV) and other common virus such as adenovirus or enterovirus depending on area

Question 6

CSF analysis: fungal meningitis

Answer 6

Appearance: Clear or cloudy
Opening pressure: Elevated
WBC count: 10-500 cells/µL
Glucose level: Low
Protein level: Elevated
Additional tests: CSF Gram stain and cultures, blood cultures, CSF bacterial antigens, CSF PCR, CSF India ink

Question 7

CSF analysis: TB meningitis

Answer 7

Appearance: Clear or opaque
Opening pressure: Elevated
WBC count: 50-500 cells/µL
Early PMNs then lymphocytes
Glucose level: Low
Protein level: Elevated
Consider additional tests: CSF Gram stain and cultures, blood cultures, CSF bacterial antigens, CSF PCR, CSF tuberculosis culture/stain looking for acid fast bacilli (AFB)

Question 8

CSF analysis: sub arachnoid haemorrhage

Answer 8

Appearance: Xanthochromia, bloody, or clear
Opening pressure: Elevated
WBC count: (1 additional WBC per 1000 RBCs is considered normal correction)
Glucose level: Normal
Protein level: Elevated
Additional tests: CSF Gram stain and culture, photospectometry to examine for xanthochromia

Question 9

CSF analysis: MS

Answer 9

Appearance: Clear
Opening pressure: Normal
WBC count: 0-20 cells/µL (lymphocytes)
Glucose level: Normal
Protein level: Usually mildly elevated (45-75 mg/dL)
Additional tests: Oligoclonal bands (paired serum and CSF)

Question 10

CSF analysis: GBS

Answer 10

Appearance: Clear or xanthochromia
Opening pressure: Normal or elevated
WBC count: Normal or elevated
Glucose level: Normal
Protein level: Elevated

Question 11

What are the three layers of meningies covering the spinal cord and brain?

Answer 11

Dura, arachnoid and pia matter?

Question 12

Where is the subarachnoid space (the space acsesed in lumbar puncture)?

Answer 12

Between the arachnoid and pia matter
Close to the ventral and dorsal columns of the spinal cord (therefore anatomical spatial awareness is crucial to performing a safe and accurate lumbar puncture)

Question 13

What is the role of CSF in the body?

Answer 13

Shock absorption
Lubrication around spinal cord
Maintaining ICP
Transportation of metabolic products

Question 14

Contraindications to lumbar puncture?

Answer 14

Suspicion of raised intracranial pressure
Anticoagulant therapy (i.e. Warfarin)
Thrombocytopenia or other clotting disorders
Suspicion of a spinal abscess
Risk of herniation (i.e. Arnold-Chiari malformation)
Acute spinal cord trauma
Congenital spinal abnormalities

CT or MRI must be performed prior to considering LP in any of above circumstances

Question 15

What equiptment is required to perform a lumbar puncture?

Answer 15

Lumbar puncture needle: recent evidence supports the use of an atraumatic needle to reduce the risk of post-procedure headaches. Needle size is based on experience and clinical judgement.
Sterile field: to cover the patient and the bed
Chlorhexidine cleaning solution (0.5 % in alcohol 70%) or alternatively iodine
Manometer: to measure the opening pressure
Sample collection containers
Local anaesthetic (typically lidocaine 1%)
Syringe (5-10ml) and needles for local anaesthetic administration (usually need one for drawing up anaesthetic and one for administration)
Dressing to apply after the lumbar puncture is complete
Pen for marking the planned insertion site

Question 16

What is used to meausre opening pressure during a lumbar puncture?

Answer 16

Manometer

Question 17

Complications associated with lumbar puncture?

Answer 17

Common:
Headache 
Bruising of skin
Bleeding
Back pain

Rare:
Infection
Cerberal herniation
Radiculopathy

Question 18

Steps in performing a lumbar puncture?

Answer 18

1. Identify insertion site
2. Position patient
3. Prepare insertion site
4. Administer local anesthetic
5. Perform a lumbar puncture
6. Measure opening pressure
7. Collect a sample of CSF
8. Remove needle and dress

Question 19

At what level should a lumbar puncture be performed?

Answer 19

Between either L3 and L4 or L4 and L5

Question 20

How should you map out the insertion site prior to a lumbar puncture?

Answer 20

Map out the insertion site on the patient:

With the patient standing, mark out L4 by joining a line between the highest points of the iliac crests.
Palpate above for L3 and below for L5.
The insertion site can be marked out either between L3/4 or L4/5 depending on the patient’s anatomical features.

Question 21

How to position a patient for a lumbar puncture?

Answer 21

After marking out the insertion site but before prepearing it:

Position the patient lying on their side in a fetal position: ask the patient to flex forwards whilst bringing their knees up towards their chest.

Question 22

How to prepare insertion site for a lumbar puncture?

Answer 22

Once site is marked out and patient is positioned:

Clean the insertion site and the surrounding area thoroughly using chlorhexidine solution and allow to dry.

Wash your hands and don sterile gloves.

Apply a sterile drape with an opening over the site of insertion.

Question 23

How should local anesthetic be administered during a lumbar puncture?

Answer 23

After marking out the site, postioning the patient and preparing the site:

Draw up the local anaesthetic and then replace the drawing needle with a new one for the injection.

Inject local anaesthesia around the site and allow time for it to take effect (at least a few minutes).

It is important to warn the patient that this will sting initially but then should quickly go numb.

Question 24

How to perform the actual lumbar puncture when performing a lumbar puncture?

Answer 24

Once the site is marked, patient positioned, site prepared and the local anesthetic has been administered for a few minuites:

Press the lumbar puncture needle to the patient’s skin over the insertion site and ask if it feels sharp (if it does, it suggests more local anaesthetic or time is needed).

If the patient is unable to feel the sharp sensation you should proceed with performing the lumbar puncture.

Advance the lumbar puncture needle through the insertion site slowly, tilted slightly cranially. The bevel of the needle should face laterally as you insert it. If using an atraumatic needle, you first insert the short introducer needle and then insert the longer atraumatic needle through this.

Three ‘pops’ are felt, as the dura is breached CSF should begin to flow through the lumen of the needle

Question 25

What layers does the needle pass through during a lumbar puncture before it reaches the subarachnoid space?

Answer 25

Skin
Subcutaneous fat
Supraspinous ligament - pop 1*
Interspinous ligament - pop 2*
Ligamentum flavum - pop 3*
Dura mater
Subdural space
Arachnoid mater

*Sudden reductions in resistance felt

Question 26

How to measure opening presure during a lumbar puncture?

Answer 26

Once CSF is flowing through the lumbar puncture needle, you can measure the opening pressure by attaching a manometer and recording at what level the meniscus of the CSF settles at. Measurement of opening pressure does not need to be performed routinely.

Question 27

How to collect a sample of CSF?

Answer 27

CSF should be collected using an aseptic non-touch technique as it drips from the back of the lumbar puncture needle.

Removal of CSF can be diagnostic (e.g. suspected meningitis) or therapeutic (e.g. benign intracranial hypertension). You should extract an appropriate volume based on your intentions (typically 8-15mL for diagnostic purposes), and place in the appropriate laboratory containers.

For some conditions, such as subarachnoid haemorrhage, it is important to number the containers sequentially so you know in which order the CSF samples were taken (this can allow you to differentiate between a traumatic tap and subarachnoid haemorrhage).

Question 28

How to remove needle following a lumbar puncture?

Answer 28

Remove, compress site with sterile gauze until dressing applied
(Dispose of needle in sharps bin, send CSF samples for laboratory analysis)