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CDHB

Lumbar Puncture

See also: Meningitis, and Subarachnoid Haemorrhage.

• RMOs should observe 2-3 lumbar punctures, then practise on a model in the Clinical Skills Unit and then perform 2-3 under direct supervision before attempting to do a lumbar puncture on their own.
• After one, or at the most two, failures an RMO should seek help from a more senior RMO or a Consultant.

Before performing the lumbar puncture:

• Always consider:
  • Does CT/MRI need to be done first? Do not perform a lumbar puncture if there is any clinical suspicion of raised intracranial pressure from a space-occupying lesion. If there is raised BP, decreased pulse, decreased level of consciousness, seizures, papilloedema, focal neurological signs, sinus, or ear infection - obtain CT/MRI head scan urgently before doing lumbar puncture.
  • Is the patient likely to bleed? Check platelets, INR and APTT and review history and examination from this perspective. Check whether the patient has recently received heparin. Lumbar punctures should not be done within 12 hours of a dose of low molecular weight heparin or if platelets <50 x 10⁹/L or if INR/APTT is abnormal.
  • Are there any other non-invasive diagnostic procedures which will give you the information you are looking for?
• You must consult the lumbar puncture protocols in the department in which you are working. If none are available, follow the guidelines given here.

  Note: The recommendations given here do not cover the administration of drugs intrathecally.

• We recommend the use of 22G pencil-point lumbar puncture needles although some departments favour 25-26G. A 22G needle is easier to use, enables accurate measurement of CSF opening pressure, and allows a sufficient flow of CSF to obtain the volume of CSF that may be required. The smaller needle may however be associated with a lower complication rate.

  Note: The pre-packaged lumbar puncture sets on the wards may not contain a pencil point needle - please check.

Performing the lumbar puncture:

• Explain the procedure, the indications, and possible complications to the patient, and obtain written consent. The patient may wish to use the toilet before the procedure.

  Note: Complications include headache, around 5% if using a pencil-point needle, nerve root injury 2%, infection less than 1%. Severe persisting headache is a rare consequence of lumbar puncture and may indicate continued leakage of CSF. There is specific treatment (application of a blood patch) which is highly effective.

• Assist with positioning the patient on their side, head flexed, knees tucked under their chin to help widen intervertebral spaces and assist in locating the intrathecal space for tapping. Place flat pillow between knees to aid correct positioning.

  Note: Sitting position with patient hunched over 1-2 pillows placed on their thigh could be considered if location of CSF is difficult in the lateral position - however, CSF pressure measurements will be uninterpretable.

• Decide before you start whether a pressure measurement is required.
• The use of an atraumatic (pencil-point) needle rather than a Quincke (cutting) needle reduces the incidence of headache from up to 25% to 5%.
• Aim for the L3-4 or L4-5 disc spaces. Use strict aseptic technique and chlorhexidine/alcohol for skin sterilization. Local anaesthetic (lignocaine 1%) infiltration of skin and subcutaneous tissue is required.
• Insert the needle through the skin and continue advancing the needle until there is decreased resistance (having traversed ligamentum flavum) or the needle has been inserted to half its length; then remove the stylet. If no CSF is obtained, replace the stylet and advance the needle about 1 mm. Wait at least 30 seconds for CSF to appear in the hub. Rotating the needle through 90-180 degrees may allow CSF to flow. Advance 1-2 mm at a time if no CSF has appeared. If no CSF is obtained when the bone is contacted or the needle is fully inserted, or when you think it has been advanced far enough, withdraw the needle very slowly until CSF flows or the needle is almost removed. Then re-insert the stylet, re-check the patient's position and needle orientation and repeat the procedure.
• When CSF flows, check the pressure if this is required. The hips should be partly unflexed since any pressure on the abdomen may falsely elevate the CSF pressure.
• Then collect samples of CSF into three plain sterile tubes and label 1, 2, and 3 in the order in which you fill them. If possible, put 2 mL CSF into each.

  The following minimum approximate volumes are required for:

  Microbiology	Culture, Gram stain, cell count and antigens	1 mL
  Biochemistry	Protein, glucose	0.5 mL
  Virology	Culture and PCR for HSV	0.5 mL
  Cytology	If abnormal cells suspected (request cytospin)	0.5 mL

  Notes:

  • Microbiology takes precedence if only a limited amount of CSF is available.
  • If oligoclonal band analysis is required, 5 mL of CSF is needed for this as well as a simultaneous venous blood sample - 5 mL clotted sample.
  • If tuberculosis is suspected, an additional 1 mL of CSF is required for further analysis.
• Encourage oral fluids afterwards. Some practitioners prefer their patients to lie flat in bed for four hours afterwards, although there is no definite evidence that this is of benefit, especially if a pencil-point needle is used.
• Give analgesia for headache. If severe headache occurs or the headache persists, then there may be ongoing CSF leakage at the puncture site. Lying flat in bed, good hydration, and in particular caffeine-containing drinks such as coffee, tea, and coke are helpful in the relief of established headache. Lying flat in bed also helps to relieve the pain which may be aggravated by an upright position. Use of a blood patch should be considered and discussed with the on-call Anaesthetist.
• It is essential to record the time and date of the procedure, the CSF pressure if taken, the volume of CSF removed, and any difficulties experienced in the clinical notes.

Topic Code: 1286