Lumbar Puncture Procedure Guideline

Indications for a lumbar puncture procedure:

1. Investigation of acute headache
• Subarachnoid haemorrhage
(NB - LP must wait for 12 hours from onset of index headache event to allow for bilirubin to be synthesisied from haem pigment in red blood cells)
• Bacterial meningitis or viral meningitis
(NB: CT Brain scan before Lumbar Puncture procedure if focal signs or reduced conscious level or HIV positive)
• Raised Intracranial Pressure due to Idiopathic Intracranial Hypertension (NB YOU MUST measure opening pressure with your patient lying on their side)
• Intracranial Venous Sinus Thrombosis (NB measure opening pressure)
2. Investigation of other nervous system diseases
• Inflammatory neuropathy (Guillain Barre Syndrome)
• Suspected multiple sclerosis (oligoclonal bands)
• Malignant meningitis (CSF sample to Cytology Lab)
3. Administration of intrathecal chemotherapy
(Only for those who have completed their intrathecal chemotherapy training)

Before Lumbar Puncture Procedure consider these....

What is your clinical diagnosis? ie, what is the indication?

Has a CT Brain scan been performed and what is the result?

• Has the film been seen by a radiologist?
• Is there a provisional or confirmed report?
• In suspected meningitis, you can proceed direct to LP without CT brain if your patient is fully conscious, has no focal neurological signs, and is not known to be HIV positive

A CT Brain is not necessary prior to a Lumbar Puncture procedure during the investigation of peripheral neuropathy, eg, Guillain Barre Syndrome

Consent

Explain the procedure to patient or relative (if patient is confused or unconscious).

The main complication of any Lumbar Puncture Procedure is a low pressure headache.

Approximately 50% of patients get spinal headaches, due to low CSF pressure if traditional cutting (Quincke type) needles are used.

An atraumatic (Whitacre type) spinal needle reduces the risk of a post-LP spinal headache to about 10%.

Only in a minority (c. 1-2%) is a post Lumbar puncture procedure headache severe enough to consider an epidural blood patch procedure.

Some patients may not be competent to give consent. You are allowed (under UK law) to proceed if there is an urgent reason to do so.

It is usually good practice to at least explain to next of kin that the procedure is needed.

Since CT Brain usually precedes a lumbar puncture procedure, the risk of tentorial or tonsillar herniation is negligible as long as imaging does not show mass effect or signs of greatly increased intracranial pressure.

Historically, before widespread use of brain imaging, great care was exercised before performing an LP as the risks of brain herniation were much greater without accurate images of the brain structure, especially with a posterior fossa brain tumour.

Lumbar Puncture Tray

1. Dressing pack
2. Sterile gloves (if not already in dressing pack)
3. Anti-septic c10mls (Chlorhexidine or Betadine)
4. 1% plain lignocaine 5ml (lidocaine)
5. Two 19G (green hypodermic needles)
6. One 22G (blue hypodermic needles)
7. One 22 gauge spinal needle 3 ½ inch length atraumatic spinal needle
8. 40cm height Manometer (pressure should be measured in every acute headache case)
9. Four sterile plain plastic or sterile glass bottles for CSF samples, 6 bottles if testing for subarachnoid haemorrhage

When testing for subarachnoid haemorrhage it is important to take three bottles and number them in order of sampling so that false positive red cell counts or false negative bilirubin absorption can be excluded.

10. Two bottle for glucose (fluoride oxalate container), one for CSF and one for blood
11. Two plain blood bottles 5ml for serum protein and paired serum oligoclonal bands
12. A 19G needle for venepuncture and 10ml syringe for venepuncture (or vacutainer or equivalent device)

Lumbar Puncture Procedure: Needle Selection

Large bore 22 gauge atraumatic needles should be used.

There is evidence that the risk of post LP headache is less if they are used.

The American Academy of Neurology now recommend using 22G atraumatic needles. See photo to see magnified picture of needle tips (Creative Commons License, from Becton Dickinson).

If 22G atraumatic needles are not available you will still need to use the bevelled tip ones, but make sure that you insert the bevel parallel to the longitudinally runing fibres of the dural sac.

Fine bore atraumatic needles, as used by anaesthetists for spinal anaesthesia (25 gauge) are not suitable for diagnostic LP as the flow of CSF is too slow for measurement of opening pressure.

Tips for a Succesful Lumbar Puncture

LP is best performed in the left lateral position (if you are a right handed operator), with the patient lying on a firm bed, parallel to the floor.

Avoid excessive neck flexion. Usually one pillow is enough for comfort. The head should not be too high relative to the lumbar spine as this will artificially elevate pressure readings by an effect of gravity alone.

Another pillow can be placed between the patients knees if it adds support and is comfortable. The patient should flex their knees and hips up to their abdomen in an attempt to try and flex the lower lumbar spine. The surface of the lumbar area should be parallel with the walls.

Identify the L3/4 intervertebral space. This is done by identifying the posterior iliac spine and drawing an imaginary line perpendicular to the floor (Tuffier's Line).

The point where these lines meet is the L3/4 interspace in over 90% of individuals. You can LP one interspinal space above or below Tuffier's Line at the L3/4 interspace or the L2/3 interspace.

Insert the needle in the midline. Aim for the umbilicus.

If you hit a firm surface it is usually bone, but occasionally tough ligaments can feel like bone and may cause anatomical confusion.

If your landmarks are correct, keep pushing the needle in.

Do not rush the needle in, try and feel your way. A sudden move in which you hit periosteum is going to provoke severe pain, and your patient will probably move out of position, making the test even more difficult for you.

When you enter the dura there is often brief resistance and then a slight "give" as you hit the subarachnoid space.

The average distance from skin to the ligamentum flavum is between 4 and 7 cm. A standard needle is 8-9cm (3.5 inches).

If your needle is in up to the hilt, you may well be offline. In very obese subjects longer needles are required to penetrate subcutaneous fat.

Consider radiological guidance in very obese subjects or those with obscured anatomical landmarks - ultrasound can be used to identify the interspinal space, and may allow real-time puncture.

X-ray screening (fluoroscopy) is the traditional method for radiological guided LP.

Pressure Measurement and Sample Collection

Once you see CSF:

1. Measure the opening pressure by connecting the manometer to the end of the spinal needle.

   • The peak pressure recorded is the opening pressure. Pressures over 25cm are definitely abnormal
   • Large surveys of lumbar puncture pressure values were performed in the 1960s in 105 normal subjects recorded opening pressures of 15cm +/- SD 3.3cm, which means that 95% will be found between 8.4cm and 21.6cm.
   • Normal pressures in obese subjects can be as high as 25cm, according to a 1985 study
   • In a seated position, which is more difficult to control, the range of opening pressures at lumbar puncture is about 39.7cm (SEM 0.4cm)
   • Proper normal values for seated lumbar puncture have never been measured, to my knowledge
   • Seated opening pressures are just not valid (unless you know how to measure the Hydrostatic Indifference Point)!
   • Low pressure can cause acute headache (usually less than 6cm, and CSF is difficult to obtain)
   • A normal pressure is usually regarded as between 8 and 20cm
   • Pressure can be artificially elevated by excessive knee flexion and increased blood pressure, obesity, anxiety, head on too large a pillow,or head up tilt on the bed
   • An isolated elevated pressure may be the only sign of venous sinus thrombosis or indicate idiopathic intracranial hypertension - so it is very important to attempt opening pressure when investigating acute headache
   • Any reason for not being able to measure opening pressure should be recorded in the patient’s notes

2. Collect the CSF.
   • The Lumbar cistern (where your needle tip is) contains about 30mls of CSF which is replaced about 4 times daily
   • You can be generous with your samples i.e. take about 2 ml (20-30 drops) per bottle
   • Risk of post-LP headache is determined by persistent CSF fistula and type of needle used, not by the amount of CSF taken.

Take the following Specimens

• Microbiology - microscopy (cell count and gram stain), PCR for meningococcus, herpes simplex virus I and II (if encephalitis is suspected)
• Immunology - oligoclonal bands, if the illness is subacute or chronic, then CSF should be sent or stored for this.

  A paired serum sample should be sent to make sure that any oligoclonal bands detected are not present in serum.

  In acute illness, oligoclonal bands need not be routinely requested.

• Cytology - if malignant meningitis is suspected, then a sample should be sent to pathology for cytological evaluation.

  If out of hours, ask Biochemistry lab to spin down and store to be forwarded to Cytology lab open.

• Biochemistry - protein and glucose, spectrophotometry for bilirubin.
  • Remember paired serum glucose
  • Bilirubin can be requested in cases of suspected subarachnoid haemorrhage. A sample for bilirubin assay should be protected from natural light, as UV radiation will degrade bilirubin.

    Bilirubin analysis does not take place out of hours, as the vast majority of people with SAH will be CT positive (95-98%).

    In CT negative cases, it is unlikely that knowing a bilirubin result a few hours earlier will influence management.

    If you have a traumatic tap, you should collect additional specimens, and label them in order 1, 2 & 3.

    This is so that you can be as certain as possible that you have not allowed traumatic tap to produce large amounts of oxyhaemoglobin to obscure bilirubin.

Sending your CSF and blood samples to the Laboratory

Clearly label, date and time all blood and CSF samples.

Try not to use vacuum delivery system, as this can agitate the CSF and produce even more oxyhaemoglobin.

However, you also need to avoid unnecessary delays, so use vacuum tube system if a porter cannot be called urgently.

Protect the biochemistry sample for spectrophotometry from light, as UV light will degrade bilirubin at a rate of 0.005 Absorption Units per hour.

Following a Lumbar Puncture Procedure please tell your patients....

Patients can mobilise as soon as they are comfortable to do so. Some people feel faint during LP, and will appreciate the chance to lie flat for half an hour.

A simple small, dry dressing or elastoplast should be applied to the needle entry site and removed 12 hours later.

The risk of CSF fistula to the skin is extremely small.

I normally recommend bed rest and a 2 litre per day oral fluid intake for spinal headaches (low pressure headaches caused by persistent CSF leak).

Common and very rare complications of a Lumbar Puncture Procedure

1. Post-lumbar puncture or spinal headache
2. Tinnitus
3. Postural nausea

Rare complications are:

1. Back ache and nerve root pain is not that common, especially if you take care not to go too far in or deviate too far off midline. (Root pain occurred in 13% on one series from 1951)

Very rare complications are:

1. Brain herniation is on the list of complications, but is unheard of if CT performed prior and posterior fossa mass or lateral mass effect is excluded on imaging
2. Subdural hygroma - if severe low pressure occurs, CSF can accumulate in the subdural space within the head
3. Epidural haematoma or subarachnoid bleeding (causing chemical meningitis) - usually more at risk of this if anti-coagulated or thrombocytopenic e.g. leukaemic case
4. Epidermoid tumour - due to use of non-styleted needle - should never happen with modern sytlet needles
5. Osteomyelitis due to passing needle through infected skin or subcutaneous tissues - avoid Lumbar puncture procedure if local skin infection at needle entry site
6. One spinal anaesthetic case in the 1950s resulted in nucleus pulposus material appearing from the spinal needle

Should Bilirubin Testing be Performed Out-of-Hours?

Patients with suspected subarachnoid haemorrhage, who have normal CT Brain, do not need to have their CSF spectrophotometry analysed and interpreted out-of-hours.

The lumbar puncture procedure does not need to wait till the next morning, but the CSF test result is not urgent.

CSF analysis can wait until the following morning, as immediate knowledge of a positive CSF is unlikely to alter overnight management.

For example, if a CT negative patient deteriorates overnight, they may need a repeat CT Brain irrespective of the CSF result (for example to detect a fresh bleed or hydrocephalus).

References