💉 Chapter 143: Lumbar Puncture

Indications (meningitis, encephalitis, subarachnoid haemorrhage, therapeutic) · Contraindications (raised ICP, coagulopathy, cardiorespiratory compromise) · Positioning (lateral recumbent) · Landmarks (L3-L4, L4-L5) · Opening pressure · CSF collection (tube order) · Complications (post-LP headache, herniation)

🔍 Core Concepts: Lumbar Puncture

📌 Indications
Diagnostic: suspected meningitis, encephalitis, SAH, Guillain-Barré, demyelinating diseases. Therapeutic: intrathecal chemotherapy/antibiotics, spinal anaesthesia.
🚫 Contraindications
Absolute: signs of raised ICP (GCS<8, focal neurology, papilloedema, brain herniation signs). Relative: coagulopathy (platelets <20-40k, INR>1.5), infection at site, cardiorespiratory compromise.
📏 Positioning
Lateral recumbent (for opening pressure) or sitting. Flex spine (fetal position) to widen interspinous spaces. Landmarks: L3-L4 or L4-L5 (line between iliac crests = L4).
🔧 Equipment
Spinal needle (pencil-point, with stylet). Needle size: 1.5" (infant), 2.5" (child), 3.5" (adult). Manometer, collection tubes.
📊 CSF Analysis
Tube 1: microbiology (culture, Gram stain, PCR). Tube 2: chemistry (glucose, protein). Tube 3: cell count/differential. Tube 4: extra (cytology, oligoclonal bands).
⚠️ Complications
Post-LP headache (most common – due to CSF leak, risk reduced with pencil-point needles). Herniation (if raised ICP). Traumatic tap, infection, subdural haematoma (coagulopathy).
🧠 CT Before LP?
Indicated if focal deficit, GCS<13, papilloedema, immunocompromise, age >60 (adults). CT does NOT quantify ICP; clinical judgment critical.

🩺 Stepwise Lumbar Puncture Technique

1
Assess contraindications
Check for signs of raised ICP (focal neurology, papilloedema, GCS<13). Coagulopathy (INR, platelets). Obtain consent.
2
Position patient
Lateral recumbent (for opening pressure) with hips/knees flexed, back curled. Line between iliac crests marks L4 level. Choose L3-L4 or L4-L5 interspace.
3
Sterile prep & anaesthesia
Chlorhexidine prep. Infiltrate lidocaine to skin and deeper tissues.
4
Insert needle
Insert spinal needle (with stylet) in midline, aiming slightly cephalad (toward umbilicus). Advance until 'pop' through ligamentum flavum. Remove stylet – CSF should drip.
5
Measure opening pressure, collect CSF
Attach manometer (if lateral position). Collect 3-4 mL in tubes. Order: tube 1 = microbiology, tube 2 = chemistry, tube 3 = cell count, tube 4 = extra. Replace stylet, remove needle. Apply dressing.