What precautions and considerations should be taken when performing a lumbar puncture?

Lumbar Puncture Procedure: Key Precautions and Considerations

The use of atraumatic (pencil-point) needles rather than conventional needles is strongly recommended for all lumbar punctures to significantly reduce complications, particularly post-dural puncture headache and other adverse events. 1

Contraindications to Lumbar Puncture

Before performing a lumbar puncture, carefully assess for these absolute contraindications:

• Signs of increased intracranial pressure:

  • Moderate to severe impairment of consciousness (GCS <13)
  • New onset seizures
  • Focal neurological signs
  • Papilledema
  • Abnormal posture or posturing 2

• Coagulopathy:

  • Current anticoagulation therapy (unless appropriately reversed)
  • Platelet count <100 × 10⁹/L
  • Rapidly falling platelet count 2

• Local factors:

  • Skin infection at the puncture site
  • Clinical suspicion of spinal cord compression 2

Pre-Procedure Assessment

1. Clinical assessment should be the primary determinant of safety rather than relying solely on CT imaging 2

2. If clinical contraindications exist:

   • Perform CT scan as soon as possible
   • Reconsider LP on a case-by-case basis after imaging
   • Do not proceed if imaging reveals significant brain shift or tight basal cisterns 2

3. If bacterial meningitis is suspected and LP is delayed:

   • Obtain blood cultures immediately
   • Start appropriate empirical antibiotics before imaging studies
   • Never delay antimicrobial therapy while awaiting CSF collection 2, 1

Procedure Technique

1. Needle selection:

   • Use atraumatic (pencil-point) needles to reduce complications
   • These needles significantly reduce post-dural puncture headache (59 fewer per 1000 patients)
   • Also reduce need for epidural blood patch, hearing disturbance, and nerve root irritation 1

2. Patient positioning:

   • Position patient in lateral recumbent position with knees drawn to chest
   • Alternatively, seated position with forward flexion can be used
   • Ensure spine is flexed to open interlaminar spaces 2

3. Strict aseptic technique:

   • Use sterile gloves, mask, and proper skin preparation
   • Create a sterile field to prevent infections 2

4. Needle insertion:

   • Identify L3-L4 or L4-L5 interspace (below termination of spinal cord)
   • Insert needle with bevel parallel to longitudinal dural fibers
   • Advance slowly until "pop" sensation of dural penetration 2

5. Opening pressure measurement:

   • Always measure opening pressure when performing LP
   • Normal values are <25 cm H₂O
   • Elevated pressure may indicate increased intracranial pressure 1, 2

CSF Collection and Testing

1. Standard CSF tests:

   • Cell count and differential
   • Glucose and protein concentrations
   • Gram stain and bacterial cultures 1, 2

2. Additional tests based on clinical suspicion:

   • Cryptococcal antigen
   • Fungal staining/cultures
   • Acid-fast bacillus smears/cultures
   • PCR tests for viral pathogens (HSV, CMV, etc.) 1, 2

3. CSF findings in common conditions:

   • Bacterial meningitis: High WBC (>2,000/μL), high neutrophils, high protein (>220 mg/dL), low glucose (<35 mg/dL)
   • Viral encephalitis: Moderate pleocytosis, mildly elevated protein, normal glucose ratio 2

Management of Complications

1. Post-dural puncture headache:

   • Most common complication (significantly reduced with atraumatic needles)
   • Treatment options include hydration, caffeine, analgesics
   • For severe cases, epidural blood patch may be necessary 1, 3

2. Increased intracranial pressure:

   • If CSF pressure is ≥25 cm H₂O with symptoms, reduce opening pressure by 50%
   • For persistent elevated pressure, repeat lumbar puncture daily until stabilized
   • Consider temporary percutaneous lumbar drains or ventriculostomy for patients requiring repeated daily LPs 1
   • Avoid mannitol, acetazolamide, and corticosteroids (unless treating IRIS) 1

3. Failed lumbar puncture:

   • Consider fluoroscopy-guided LP for patients with difficult anatomy (obesity, spinal deformities) 2
   • For patients with ventricular devices, CSF can be sampled directly from the reservoir 1

Special Considerations

1. Cryptococcal meningitis management:

   • Daily lumbar punctures may be required to manage increased intracranial pressure
   • Remove a volume of CSF that halves the opening pressure (typically 20-30 mL)
   • Consider CSF shunting for patients who cannot tolerate daily LPs 1

2. Non-diagnostic initial LP:

   • Consider a second LP 24-48 hours later if clinical suspicion remains high
   • In viral encephalitis, approximately 5-10% of adults with proven HSV encephalitis may have normal initial CSF findings 2

3. Informed consent:

   • Discuss potential risks including post-dural puncture headache, back pain, infection, and rare neurological complications
   • Explain the necessity of the procedure and potential alternatives 2

The use of atraumatic needles represents a simple yet highly effective modification to standard LP technique that significantly improves patient outcomes with minimal additional training required 1. Despite this clear evidence, adoption of atraumatic needles remains suboptimal in many clinical settings, representing an important opportunity to improve patient care.