DO NOT USE FOR CLINICAL PRACTICE
Please use current guidelines available on the UHNM intranet for patient treatment
Please use current guidelines available on the UHNM intranet for patient treatment
INDICATIONS
Diagnosis
Table: Indications for diagnostic LP
Indications | Tests |
Suspected SAH | CSF xanthochromia, glucose and protein plus Blood test for LFT's, glucose and protein |
Myelopathies and suspected multiple sclerosis (but not if spinal cord compression suspected) |
Protein, IgG or gammaglobulin, oligoclonal bands (N.B. take paired blood sample) |
Acute or demyelinating peripheral neuropathies (e.g. Guillain-Barré syndrome) | Cells, protein |
Infections of CNS (e.g. bacterial meningitis, tuberculosis, acute and subacute encephalitides, neurosyphilis, viral, fungal, and protozoal meningitis) | Gram stain, cells, protein, treponemal serology, glucose, culture, special stains, and antibodies |
Meningeal infiltration | Cytology |
Suspected idiopathic (formerly 'benign') intracranial hypertension | Opening CSF pressure |
Suspected subarachnoid haemorrhage (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)
Management
- Introduction of contrast media - see Contrast associated acute kidney injury: Prevention 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 (see 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
- CSF is usually diffusely bloodstained in all 3 tubes, but the 3-tube test should not be relied upon to exclude SAH
SPECIMENS
- Requests depend on clinical problem (see Table)
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)
- If further investigations may be required over the next few days, take an extra container(s) and send to virology and microbiology with a request to 'please store sample'
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)
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)
- Send to 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
- Note: 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
- Prescribe regular analgesics (paracetamol and/or codeine) with anti-emetics if required e.g. ondansetron 4 mg 8-hrly oral/IV
- if codeine prescribed, monitor for constipation