Procedures

Lumbar puncture in the ICU

Reviewed Nov 2026·4 references
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When to scan first, anticoagulant timing, technique, opening pressure and CSF tests.

Definition
LP is needed for suspected meningitis/encephalitis, subarachnoid haemorrhage with negative CT, Guillain-Barré syndrome and some neurological disorders. Never delay antibiotics for imaging or LP in suspected bacterial meningitis.

At the bedside

Timed steps
  1. 1

    Antibiotics first

    Within 1 h

    If bacterial meningitis is suspected and LP will be delayed, take blood cultures and give antibiotics (and dexamethasone) immediately.

  2. 2

    CT before LP if

    Focal neurological deficit, new-onset seizures, GCS < 10, severe immunocompromise (ESCMID).

  3. 3

    Coagulation and anticoagulants

    Prophylactic LMWH: wait 12 h; therapeutic LMWH: 24 h; SC UFH 5,000 units: 4-6 h; apixaban/rivaroxaban: 72 h; clopidogrel: 5-7 days; warfarin: normal INR. Platelets commonly ≥ 50 × 10⁹/L.

  4. 4

    Position and technique

    Lateral decubitus (for accurate opening pressure) at L3/4 or L4/5; atraumatic (pencil-point) needle reduces post-dural puncture headache.

  5. 5

    Opening pressure

    Measure with a manometer in lateral position, legs extended; normal about 10-20 cmH₂O; > 25 cmH₂O is raised (consider cryptococcal meningitis, IIH, venous sinus thrombosis).

  6. 6

    Samples

    Cell count (tubes 1 and 4 for SAH), protein, glucose with paired plasma glucose, Gram stain and culture, PCR (HSV, enterovirus), cryptococcal antigen, AFB/GeneXpert, xanthochromia (> 12 h after SAH onset).

Local anaesthetic

Lidocaine (lignocaine)

Infiltration
Dose
1-2% lidocaine; stay under 4.5 mg/kg plain
Worked example
70 kg: max ~300 mg plain = 30 mL of 1% (10 mg/mL) or 15 mL of 2%.

CSF patterns

PatternCellsProteinGlucose ratio
Normal< 5/µL lymphocytes0.15-0.45 g/L≥ 0.6
BacterialHundreds-thousands, neutrophilsHigh (> 1 g/L)< 0.4
Viral10-500, lymphocytesNormal-mildly highNormal
TB / fungal50-500, lymphocytesHigh (often > 1-2 g/L)Low
Red flag · call your senior now
Deterioration after LP (falling GCS, new pupil asymmetry) - suspect herniation; treat raised ICP and image urgently.
Pitfall
Delaying antibiotics for CT and LP.
Pitfall
Doing LP on therapeutic LMWH or a DOAC without checking timing.
Pearl
CSF:blood glucose ratio < 0.4 is more useful than an absolute CSF glucose in hyperglycaemic patients.

References

  1. 1

    van de Beek D, Cabellos C, Dzupova O, et al. ESCMID guideline: diagnosis and treatment of acute bacterial meningitis. Clin Microbiol Infect 2016;22(Suppl 3):S37-62.

  2. 2

    Horlocker TT, Vandermeuelen E, Kopp SL, et al. Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: American Society of Regional Anesthesia and Pain Medicine evidence-based guidelines (fourth edition). Reg Anesth Pain Med 2018;43:263-309.

  3. 3

    Nath S, Koziarz A, Badhiwala JH, et al. Atraumatic versus conventional lumbar puncture needles: a systematic review and meta-analysis. Lancet 2018;391:1197-204.

  4. 4

    Neal JM, Barrington MJ, Fettiplace MR, et al. The third American Society of Regional Anesthesia and Pain Medicine practice advisory on local anesthetic systemic toxicity: executive summary 2017. Reg Anesth Pain Med 2018;43:113-23.

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