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Lumbar puncture (LP) [advanced]

Before you start

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

Introduction

  • 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; damage to local structures (including nerves)
  • Perform CT head pre-LP 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)
    • 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

Preparation

  • 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 facing towards the patient head)
    • 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 ( ̴ 5cm depth) where you may feel a ‘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
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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 → microbiology
      • Protein and glucose tube 2 → biochemistry
      • Xanthochromia tube 4 → biochemistry (if required; keep this sample dark in an envelope)
      • Others e.g. oligoclonal bands, PCRs (meningococcal, VZV, HSV)
    • Grey biochemistry tube
      • Glucose → biochemistry
  • Perform venepuncture to determine concurrent blood glucose level
  • Fully document LP procedure in patients notes
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