Indications
- Suspected meningitis/encephalitis — CSF culture, cell count and PCR guide antimicrobial duration and diagnosis. Never delay empirical antibiotics/antivirals to obtain an LP.
- Subarachnoid haemorrhage workup when CT is negative — LP remains part of the diagnostic pathway, though practice is evolving as modern CT sensitivity within 6 hours of headache onset is very high; discuss with your local neurosurgical/stroke pathway, as some units now accept a negative CT within 6 hours as sufficient to exclude SAH without LP.
- Idiopathic intracranial hypertension — opening pressure measurement and symptomatic relief.
Contraindications & cautions
Contraindications
- Signs of raised intracranial pressure with risk of coning — focal neurology, reduced GCS, papilloedema, seizures.
- Coagulopathy or therapeutic anticoagulation — correct where possible before proceeding.
- Significant thrombocytopenia — a platelet count around 40–50 × 10⁹/L is commonly used as a working threshold, though evidence for a single "safe" cut-off is limited; discuss with haematology in borderline or leukaemic patients.
- Local skin/soft tissue infection at the puncture site.
When to CT before LP
- Reduced conscious level or fluctuating GCS.
- Focal neurological signs.
- New seizures.
- Immunocompromise (risk of mass lesion, e.g. toxoplasmosis, lymphoma).
- Papilloedema on fundoscopy.
Consent & preparation
- Explain the procedure, sensations expected, and the common risk of post-LP headache; discuss bleeding, infection and (rare) neurological injury.
- Baseline observations; check recent coagulation and platelet results if relevant risk factors exist.
- Full aseptic technique — sterile gloves, drapes, skin preparation, and a no-touch technique for the needle track.
Equipment
Positioning & landmarks
Lateral decubitus position with the spine flexed ("fetal position") is preferred if an accurate opening pressure is needed — pressure readings taken sitting up are unreliable. The intercristal (Tuffier's) line, joining the top of the iliac crests, crosses the spine at approximately L4; use the L3/4 or L4/5 interspace to stay below the spinal cord (which ends around L1/2 in adults).
Step-by-step technique
Position and mark
Lateral decubitus with knees drawn to chest and chin tucked (or sitting flexed forward if opening pressure is not required). Palpate the intercristal line and mark the chosen interspace.
Aseptic prep and local anaesthetic
Full aseptic technique; infiltrate skin and deeper tissues along the intended track with lidocaine.
LAST rescue — AAGBI algorithm ↗Insert the needle
Advance the atraumatic needle (bevel/opening orientated parallel to the long axis of the spine) in the midline, angled slightly cephalad toward the umbilicus. Use a stylet throughout; a subtle "give" is often felt as the needle passes the ligamentum flavum and dura.
Measure opening pressure
Withdraw the stylet, attach the manometer promptly, and record the opening pressure with the patient relaxed and legs extended.
Collect samples
Collect CSF sequentially into numbered tubes: cell count, protein, paired glucose (send a serum glucose at the same time), microscopy/culture ± viral PCR, and a dedicated tube for xanthochromia protected from light.
Reinsert stylet before withdrawal
Replace the stylet before withdrawing the needle — this reduces the risk of nerve root entrapment in the dural sheath.
Dress and reassess
Apply a dressing; advise the patient on lying flat if uncomfortable and on post-LP headache symptoms to watch for.
Complications
Common
- Post-dural-puncture headache — reduced by using an atraumatic (pencil-point) needle rather than a cutting-tip needle; strong evidence supports this across ages and indications.
- Backache and local discomfort.
- Minor bleeding at the site.
Rare but serious
- Cerebral or cerebellar herniation — the reason for careful patient selection and pre-LP CT where indicated.
- Spinal or epidural haematoma, especially with coagulopathy.
- Infection (meningitis from the procedure itself) — strict asepsis is essential.
- Nerve root irritation from needle trauma.
Post-LP headache management
- Typically postural — worse sitting/standing, better lying flat; onset usually within 24–48 hours.
- First-line: simple analgesia, hydration, caffeine, and reassurance that most resolve within days.
- Persistent or severe headache unresponsive to conservative measures — consider referral for an epidural blood patch, usually via anaesthetics.
- Using an atraumatic needle at the time of the original LP is the most effective preventive measure available.
DOPS pointers
RCEM curriculum: Core Procedural Skill. What assessors look for at each entrustment level:
| 1 | Observed only — describes indications, contraindications and when CT is needed first. |
| 2a | Performs with supervisor scrubbed alongside: correct landmarks, aseptic technique, sample sequence. |
| 2b | Performs with supervisor in department: manages opening pressure measurement and documentation independently. |
| 3 | Anticipates and manages a difficult LP (obesity, previous surgery, dry tap) and knows when to stop and image-guide. |
| 4 | Independent; teaches and supervises others. |
References
- NICE. Meningitis (bacterial) and meningococcal disease: recognition, diagnosis and management. NICE guideline NG240, 2024.
- Rice CM, et al. Atraumatic (pencil-point) versus conventional needles for lumbar puncture: a clinical practice guideline. BMJ Rapid Recommendation, 2018.
- Bodilsen J, et al. Comparison of international guidelines for CT prior to lumbar puncture in suspected meningitis. 2024.
- British Society for Haematology and related literature on platelet thresholds for lumbar puncture — thresholds vary; discuss borderline cases with haematology.