Lumbar puncture technique and indications

Lumbar puncture technique and indications

Lumbar puncture technique and indications

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💉 Why We Tap

LP is performed for both diagnostic and therapeutic reasons.

  • Diagnostic (CSF Analysis & Pressure)

    • Infection: Suspected meningitis or encephalitis.
    • Hemorrhage: Suspected subarachnoid hemorrhage (SAH) with a negative head CT.
    • Inflammation: Multiple sclerosis (oligoclonal bands), Guillain-Barré syndrome (albuminocytologic dissociation).
    • Malignancy: CNS lymphoma, leptomeningeal metastases.
    • Pressure: Measure opening pressure (e.g., idiopathic intracranial hypertension [IIH]).
  • Therapeutic

    • Relieve ↑ intracranial pressure (e.g., large volume tap in IIH).
    • Administer intrathecal medications (e.g., chemotherapy, anesthetics, antibiotics).

⭐ In suspected SAH with a negative non-contrast head CT, an LP is the definitive next step to check for xanthochromia or RBCs.

⚠️ Clinical Correlations - Danger Zones

The primary risk of LP is iatrogenic cerebral herniation. Always assess for contraindications before proceeding.

Absolute ContraindicationsRelative Contraindications
• Infection at puncture site• Coagulopathy (Platelets < 50,000/μL, INR > 1.5)
• Signs of ↑ ICP / mass lesion• Severe spinal deformity
• Suspected spinal epidural abscess• Brain abscess (risk of seeding)

💉 The Needle's Path

  • Positioning: Lateral decubitus (fetal position) or sitting upright, maximally flexed to open interspinous spaces.
  • Landmark: A line connecting the superior iliac crests crosses the L4 spinous process.
  • Insertion: L3-L4 or L4-L5 interspace. Needle with bevel up (parallel to dural fibers), angled slightly cephalad.

Lumbar Puncture Needle Path in Spinal Column

⭐ A distinct "pop" is felt as the needle pierces the ligamentum flavum and a second, finer pop for the dura-arachnoid membrane.

📌 Skinny Suzan Is Always Laying Down Asleep: Skin, Subcutaneous, Supraspinous, Interspinous, Ligamentum flavum, Dura, Arachnoid.

🧪 Diagnosis - Decoding the Fluid

Analyze CSF via 4 tubes: 1) Cell count/differential, 2) Gram stain/culture, 3) Glucose/protein, 4) Special tests (e.g., oligoclonal bands, VDRL). Classic findings differentiate key CNS pathologies.

ConditionOP (cmH₂O)WBC/μL (Diff)Glucose (mg/dL)Protein (mg/dL)
Bacterial↑↑ (>25)↑↑ (>1000, PMNs)↓↓ (<40)↑↑ (>200)
ViralN/↑ (<25)↑ (<1000, Lymphs)NormalN/↑ (<150)
Fungal/TB↑ (<500, Lymphs)↓ (<45)↑ (>150)
SAH↑↑ RBCsNormal

🤕 Complications - The Aftermath

  • Post-LP Headache: Most common. Orthostatic (worse upright, better supine) from CSF leakage.
  • Infection: Iatrogenic meningitis (rare).
  • Bleeding: Epidural/subdural hematoma, esp. with coagulopathy.
  • ⚠️ Herniation: Fatal risk if ↑ICP with a mass lesion.

⭐ Treat post-LP headache with bed rest, hydration, and caffeine; consider an epidural blood patch for severe, refractory cases.

⚡ Biggest Takeaways

  • Insert needle at the L3/L4 or L4/L5 interspace (level of iliac crests); the spinal cord ends at L1-L2 in adults.
  • Absolute contraindication: Signs of increased ICP (e.g., papilledema); risk of cerebral herniation. Get a CT head first if suspected.
  • Key indications: Suspected meningitis, subarachnoid hemorrhage (SAH), Guillain-Barré syndrome, and multiple sclerosis.
  • Needle pierces ligaments (ligamentum flavum gives a "pop"), dura, and arachnoid mater.
  • Use the lateral decubitus position to accurately measure opening pressure.

Practice Questions: Lumbar puncture technique and indications

Test your understanding with these related questions

A 22-year-old female is brought to the emergency department by her roommate with a one day history of fever and malaise. She did not feel well after class the previous night and has been in her room since then. She has not been eating or drinking due to severe nausea. Her roommate checked on her one hour ago and was alarmed to find a fever of 102°F (38.9°C). On physical exam temperature is 103°F (40°C), blood pressure is 110/66 mmHg, pulse is 110/min, respirations are 23/min, and pulse oximetry is 98% on room air. She refuses to move her neck and has a rash on her trunk. You perform a lumbar puncture and the CSF analysis is shown below. Appearance: Cloudy Opening pressure: 180 mm H2O WBC count: 150 cells/µL (93% PMN) Glucose level: < 40 mg/dL Protein level: 50 mg/dL Gram stain: gram-negative diplococci Based on this patient's clinical presentation, which of the following should most likely be administered?

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Flashcards: Lumbar puncture technique and indications

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Schwannomas are treated with _____ and/or stereotactic radiosurgery

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Schwannomas are treated with _____ and/or stereotactic radiosurgery

resection

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