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Lumbar puncture (LP) [advanced]

Please note content is for educational purposes only and procedures should not conducted based on this information. OSCEstop and authors take no responsibility for errors or for the use of any content.

Indications: diagnosis or exclusion of possible meningitis, subarachnoid haemorrhage or CNS diseases (e.g. GBS, MS); relief of idiopathic intracranial hypertension

Contraindications: ↑ICP; midline shift; brain abscess; coagulopathy (INR >1.4, platelets <50, therapeutic anticoagulant <24 hours, clopidogrel <7days); infection over puncture site


  • Wash hands, Introduce self, Patients name & DOB & wrist band, Explain procedure and get written consent
    • Common risks: headache; bleeding/haematoma; paraesthesia; pain; infection; failure
    • Rare risks: brain herniation; CSF leak; nerve damage
  • Perform CT head pre-LP for meningitis if: risk of ↑ICP (suggested by ↓GCS, focal neurology, pupil abnormalities, papilloedema, seizures); immunocompromised; known CNS lesion
  • **Check patients clotting screen, platelet count and if they have been on an therapeutic anticoagulant/clopidogrel**
  • Ensure assistant is available and make sure there is a chair for you to sit on next to the patient

Preparation part

  • Wash hands and apply apron
  • Clean a trolley
  • Gather equipment onto bottom of trolley (think through what you need in order)

Equipment list

  • Sterile pack
  • Cleansing snap-sponge (iodine or alcohol/chlorhexidine) x2
  • Sterile drape with hole in centre (or 2-3 drapes without holes in)
  • 10ml syringe and 3 needles (1 blunt fill 18G drawing-up needle, 1 orange 25G, 1 green 21G) for local anaesthetic
  • Lumbar puncture equipment
    • Spinal needle (usually start with black 22G needle, or less flexible yellow 20G needle in larger patients)
    • LP manometer
  • Cotton gauze swabs (used whenever needed throughout procedure to dry/clean sterile area)
  • Sterile dressing
  • Equipment to be kept outside of the sterile field
    • Sterile gloves
    • 10ml 1% lidocaine (maximum 3mg/kg – note 1ml 1% lidocaine = 10mg)
    • 4 white-topped sample collection bottles (labelled with biro 1-4)
    • 1 grey biochemistry sample bottle for glucose

  • Walk to patient
  • Wash hands
  • Open sterile pack to form a sterile field on the top of the trolley
  • Open packets (without touching the instruments themselves) and drop sterile instruments neatly into the sterile field
  • Pick up waste bag from sterile pack without touching anything else and stick to side of trolley

Patient part

Positioning and exposure

  • Expose patient’s back
  • Position patient
    • Lying on their left-hand side on a flat bed with their neck, hips and knees flexed as much as possible (foetal position)
    • Ask them to hold their knees as close to their chest as possible and touch their chin on their chest
    • Place a pillow between their knees and under their head
  • Locate insertion point:
    • Identify iliac crests
    • The disk space in the horizontal plane between the iliac crests is L3-4
    • The insertion point is mid-way between the L3/L4 (or L4/L5) spinous processes
  • Mark insertion point with a skin pen/indentation


  • Wash hands
  • Apply sterile gloves using sterile technique (open pack on a side surface)
  • Sterilize area
    • Work from middle outwards in one spiral motion (use cleansing snap-sponge)
    • Repeat this with 2nd cleansing snap-sponge
    • Ensure you also clean the iliac crests (for repeat palpation)
    • Discard used snap-sponges as they are no longer sterile, but note all equipment used after this (including all needles) can be returned to the sterile field after use
    • Apply the sterile drape over the patient’s body so that the hole is in the correct place to allow access to the insertion site (or apply 2-3 drapes centred around exposed insertion site if no holes)
  • Anaesthetise tract
    • Ask assistant to snap open lidocaine bottle and hold open upside-down
    • Draw up lidocaine using drawing-up needle on 10 ml syringe
    • Change to the orange needle and insert at an acute angle to form a single subcutaneous bleb around insertion site in order to anaesthetise the skin
    • Change to the green needle and insert perpendicular to the skin to anaesthetise the insertion tract
      • This is done by instilling lidocaine in small increments of increasing depth
      • Always aspirate when advancing the needle (so you know if you get to the subarachnoid space) and aspirate before injecting lidocaine (to check you are not in a vessel)
      • Stop if CSF is aspirated (this will not occur in most people because the needle will not be long enough to enter the subarachnoid space)
      • Leaving the needle in (so you do not lose the position), disconnect syringe and wait 1 minute to take effect
  • While waiting for anaesthetic to work, assemble manometer if unassembled

Performing the LP

  • Needle insertion
    • Remove green needle used to anaesthetise the tract
    • Insert the spinal needle perpendicular to the skin aimed towards the umbilicus at the same insertion point as the green needle (with the bevel oriented upwards)
    • Use both hands – one gently holding needle close to skin to angle it, the other holding the needle slightly distally to provide necessary force
    • Slowly advance through the insertion tract, regularly withdrawing the stilette at small increments of increasing depth (observing for drips of CSF to determine if you are in the subarachnoid space)
    • The subarachnoid space is deep to the dura ( Μ΄ 5cm depth) where you may feel a β€˜give’
    • If you strike bone at any point, withdraw the needle slightly, re-angle and advance again
    • Once you are in the subarachnoid space, CSF sill start to drip from the needle when you withdraw the stilette
  • Pressure measurement
    • Remove the stilette and place back into sterile field
    • Connect the manometer to the needle via the 3-way tap (off switch pointing posteriorly to close posterior tap)
    • CSF will rise up the manometer
    • Note the pressure at the point it stops rising
  • Sample collection
    • Ask the assistant to place the collection bottles under the posterior tap in labelled order
    • When ready, turn the 3-way tap off switch anteriorly to close the tap connected to the spinal needle – allowing CSF to drip from the manometer gage into the collection tubes
    • When all the CSF from the manometer gage is used up, turn the 3-way tap off switch superiorly, to allow CSF to bypass the manometer gage and drip straight from the patient into the tubes
    • Collect 10-15 drops into each tube
    • Lastly, ask assistant to collect 5-10 drips into grey biochemistry tube
  • Completion
    • Remove the manometer and 3-way tap
    • Replace the stilette and then remove the needle (reduces headache incidence)
    • Apply a sterile dressing
LP manometer

To complete

  • Thank patient and cover them
  • Advise patient to stay lying for at least 1 hour
  • Ask nurses to perform neurological observations twice during the hour
  • Dispose of sharps safely; bin waste and gloves; clean trolley and wash hands
  • Label sample tubes and urgently send to lab for
    • White sample tubes (labelled 1-4)
      • MC&S x2 – tubes 1 and 3 β†’ microbiology
      • Protein and glucose – tube 2 β†’ biochemistry
      • Xanthochromia – tube 4 β†’ biochemistry (if required; keep this sample dark in an envelope)
      • Others e.g. oligoclonal bands, PCRs (meningococcal, VZV, HSV)
    • Grey biochemistry tube
      • Glucose β†’ biochemistry
  • Perform venepuncture to determine concurrent blood glucose level
  • Fully document LP procedure in patients notes

Learn how to interpret the results too…

Cerebrospinal fluid result interpretation is covered here!

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