Synopsis
Select, prepare and perform lumbar puncture safely, preserve diagnostic yield and interpret opening pressure and cerebrospinal-fluid results in relation to timing, serum measurements and clinical probability.
- Define the question before puncture: infection, inflammation, subarachnoid haemorrhage, malignant infiltration, pressure disorder and therapeutic drainage require different timing, tubes, paired blood tests and laboratory handling.
- Obtain consent covering purpose, alternatives, discomfort, bleeding, infection, post-dural-puncture headache, failure and the rare risk of neurological deterioration when contraindications are missed.
- Check observations, conscious level, focal signs, optic discs where competent, anticoagulants, antiplatelets, platelet count and coagulation context, spinal anatomy, local infection and cardiorespiratory ability to tolerate positioning.
Key red flags
Raised opening pressure, turbid fluid, neutrophilic pleocytosis, increased protein and reduced CSF glucose relative to blood supports bacterial meningitis, but prior antibiotics, early disease and immunosuppression can alter every component.
Investigation priorities
Measure subarachnoid pressure for suspected intracranial hypertension, infection and selected other syndromes.
Management branches
Fever, headache, meningism, altered behaviour, reduced consciousness, focal deficit, rash or seizure creates concern for meningitis or encephalitis.
- Perform ABCDE, obtain blood cultures and other immediate samples and start guideline-concordant empirical antibiotics and, when indicated, aciclovir and adjunctive therapy without waiting for imaging or LP if delay would result.
- Assess cardiorespiratory stability, conscious level, focal signs, papilloedema risk, recent seizure and haemostasis to decide whether puncture can occur now or needs CT and specialist review first.
Key medicines
Lidocaine 1% local anaestheticInfiltrate the skin and deeper tract incrementally after aspiration, using the smallest effective volume and remaining below the local maximum dose, commonly 3 mg/kg without adrenaline.