INDICATIONS
Diagnosis
Suspected SAH
- Perform LP only if scan negative in face of reasonable clinical suspicion, and at least 12 hr after onset of symptoms (e.g. headache)
- Tests
- CSF xanthochromia, glucose and protein plus
- Blood test for LFT’s, glucose and protein
Myelopathies and suspected multiple sclerosis
If spinal cord compression suspected, do not perform LP
- Tests
- protein, IgG or gammaglobulin,
- oligoclonal bands
- N.B. take paired blood sample
Acute or demyelinating peripheral neuropathies
- e.g. Guillain-Barré syndrome
- Tests
- cells, protein
Infections of CNS
- e.g. bacterial meningitis, tuberculosis, acute and subacute encephalitides, neurosyphilis, viral, fungal, and protozoal meningitis
- Tests
- gram stain, cells, protein, treponemal serology
- glucose, culture, special stains, and antibodies
Meningeal infiltration
- Tests
- cytology
Suspected idiopathic intracranial hypertension
- Tests
- opening CSF pressure
Introduction of contrast media
- See Prevention of contrast induced acute kidney injury guideline
Introduction of chemotherapeutic agents
- e.g. in leukaemia
CONTRAINDICATIONS
- Raised intracranial pressure. Request CT scan
- indicated by morning or postural headache, vomiting, and papilloedema
- in patients with acute headache and reduced conscious level, a normal CT scan result can be falsely reassuring – see Community-acquired meningitis guideline
- danger is of fatal transtentorial or cerebellar ‘coning’
- Suspected spinal cord compression. MR scan is investigation of choice
- diagnostic LP does not distinguish intrinsic lesion (e.g. multiple sclerosis) from extrinsic compression by disc or tumour
- Local sepsis
- puncture through infected skin carries risk of meningitis
- Coagulopathy
EQUIPMENT
- Sterile gloves
- Green sterile towel and drapes
- Dressing pack with cotton balls, gauze swabs, gallipot
- Skin antiseptic
- Lidocaine 2% plain injection in 5 mL syringe with orange (25 G) and green (21 G) needles
- LP needles (22 G): 3 and 3.5 inches long
- prefer atraumatic needle for elective LP
- Manometer
- Specimen containers (3 clear glass, 1 grey top plastic) for microscopy/culture, protein, other tests (if indicated), and glucose, respectively. See SPECIMENS
- if further investigations may be required over the next few days, take an extra container(s) to send to microbiology and virology with a request to ‘please store sample’
- Adhesive dressing
PROCEDURE
- If not competent in procedure, organise supervision by a clinician experienced in the procedure
Preparation
- Appoint and brief assistant
- Number the 3 (or more, see above) clear glass bottles (1, 2, 3)
Consent
- Explain procedure, inform patient of symptoms that may follow procedure, and reassure
- Obtain and record written consent – see Consent guideline
Position of patient and puncture
- Place patient on left side with back against edge of bed, neck slightly flexed, and both legs drawn up towards chest
- consider placing pillow between patient’s legs to ensure that back is perpendicular to bed, and raise bed to comfortable height
- Palpate anterior superior iliac crest. L3–4 interspace is apparent as a palpable gap lying perpendicularly beneath it, but L2–3 or L4–5 are equally acceptable sites
- Mark skin over chosen interspace about 1 cm inferior to tip of adjacent spinous process
Aseptic technique
- Wash hands and put on gloves
- Cleanse patient’s skin and position sterile drapes
- Assistant opens all packs including syringes and needle, shaking sterile contents onto sterile towel
- Check all equipment fits
- Draw up lidocaine while assistant holds lidocaine bottle
- Stretch patient’s skin evenly over interspace, infiltrate skin and deeper tissues with lidocaine (orange needle for skin and green needle for deeper tissues)
- allow at least 1 min for lidocaine to work
- Introduce LP needle at 90° to back, with bevel in sagittal plane (to minimise size of hole) and pointing slightly towards head
- Push through resistance of superficial supraspinous ligament and negotiate interspinous ligament to meet firmer resistance of ligamentum flavum at about 4–7 cm
- An extra push results in a popping sensation as dura is breached and needle enters subarachnoid space
- Withdraw stylet and clear colourless fluid should drip out
- Measure CSF pressure, then collect CSF specimens with assistant holding CSF bottles
- After CSF collected and while still sterile, replace LP stylet into introducer and withdraw LP needle
Dry tap
- If no fluid emerges or fluid does not flow easily, rotate needle – a flap of dura may be lying against bevel
- If there is still no fluid, reinsert stylet and cautiously advance, withdrawing stylet after each movement
- pain radiating down either leg indicates that needle is too lateral and has hit nerve roots. Withdraw needle almost completely, check patient's position, and reinsert in midline
- If needle meets total obstruction, do not force it: it may be lying against an intervertebral disc and could damage it. Again, withdraw, check position, and reinsert
- If there is complete failure, move one space up or down depending upon original position
- Procedure may be easier if patient is sitting up, although this would preclude measurement of CSF pressure
- Dry tap usually results from faulty technique
- after 2 or 3 attempts ask someone more experienced for help
- rare causes of genuine dry tap are arachnoiditis, meningeal infiltration and true low CSF pressure
Manometry
- When CSF flows freely, connect manometer to needle hub
- Ask assistant to hold top and record pressure (normal 80–180 mm CSF)
- height of meniscus should change with respiration
Low pressure
- Most common cause is poor needle placement
- if genuine, do not try to aspirate as CSF flow may be obstructed by cerebellar tonsil herniation or spinal block
- In either case, seek a neurological opinion
Raised pressure
- Slightly raised CSF pressure in very anxious or obese patient may be ignored
- Investigate pressures >250 mm as abnormal
- if greatly raised pressure is discovered in clear fluid, collect CSF from the manometer to provide specimens
- ask patient to 'uncurl' to see if pressure falls once abdominal compression relieved
- if still raised despite this manoeuvre, withdraw needle immediately and seek neurological opinion
Bloodstained tap
- Collect bloodstained fluid in 3 tubes
Traumatic tap
- Blood forms streams in otherwise clear CSF
- The first 3 consecutive specimens show clearing of blood and usually become less obviously coloured, with a corresponding fall of the red cell count
Subarachnoid bleeding
SPECIMENS
- Requests depend on clinical problem
- If taking CSF samples for both diagnostic microbiology and suspected SAH, take samples for microbiology first
Diagnostic microbiology
Possible specimens
- Gram stain, cells, protein, treponemal serology
- Glucose, culture, special stains, and antibodies
- For routine bacterial culture, always obtain 1 mL in sterile container
- if TB meningitis suspected, obtain additional ≥5 mL for TB culture
- if pre-treated with antimicrobials and meningococcal meningitis suspected, obtain additional 1 mL in separate sterile container for meningococcal PCR
- if herpes simplex virus meningo-encephalitis suspected, obtain additional 1 mL in separate sterile container for HSV PCR
- request other CSF PCR tests according to suspected pathogen(s)
Suspected SAH
CSF glucose
- CSF into fluoride oxalate bottle and send to clinical biochemistry
CSF xanthochromia and protein
- CSF into 3 plain bottles (minimum volume 1 mL in each bottle)
- Place last of 3 plain bottles to be filled in dark container (protected from light)
Blood tests
- LFT’s, glucose and protein
Transport and biochemistry
- Provide following information with sample
- time between onset of symptoms and LP
- results of CT scan. Xanthochromia screening will normally be performed only where CT scan is negative
- date of any previous LP. Xanthochromia screening is misleading after recent LP
- Send to clinical biochemistry (do not use pneumatic tube system)
- Contact clinical biochemistry, ask for senior member of staff or bleep duty biochemist
- explain that CSF sample is being sent for xanthochromia screening
Myelopathies and suspected multiple sclerosis
- Protein, IgG or gammaglobulin
- Oligoclonal bands
- N.B. take paired blood sample
Acute or demyelinating peripheral neuropathies
- Cells, protein
Meningeal infiltration
- Cytology
AFTERCARE
- Headache is best prevented by careful technique, use of a small gauge needle and ensuring adequate fluid intake for first 24 hr
- lying down after LP does not reduce the incidence of headache
Postural headache
- Significantly worsened by sitting and/or standing from supine position and improved by lying
- Occurs in about 20–30% of patients
- May be accompanied by vomiting, and may not occur for 3–4 days
- It usually lasts 36–72 hr, but can occasionally persist for a week
Management
- Lie patient flat, bed tilted head down
- Liberal use of analgesics (paracetamol or codeine phosphate) with
- anti-emetics – metoclopramide (duration max 5 day) or domperidone (duration max 7 day)
© 2022 The Bedside Clinical Guidelines Partnership.
Created by University Hospital North Midlands and Keele University School of Computing and Mathematics.
Research and development team: James Mitchell, Ed de Quincey, Charles Pantin, Naveed Mustfa