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; nerve damage
• 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)

• 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 2^nd 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 ( ̴ 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

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