Table of Contents
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)
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
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 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
- White sample tubes (labelled 1-4)
- 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!