Lumbar puncture

Indications

Proper needle trajectory: skin, subcutaneous tissue, supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space (containing internal vertebral venous plexus), dura, arachnoid, and subarachnoid space

Surface markings for lumbar puncture. Blue dots = Iliac crests; line connecting them = intercristal (Tuffier's) line; intersection of the Tuffier's line and lumbar spine midline = L4 spinous process.

Contraindications

• Infection at LP site
• Suspected spinal epidural abscess

Lumbar puncture if coagulopathic

• Tranfuse if platelets <25,000
• INR >1.5
• Hemophilia, von Willebrand disease, other coagulopathies
  • If hemophiliac, replace factor before LP

CT Before Lumbar Puncture

LP without CT is likely safe if:

• History
  • Age < 60
  • Not immunocompromised
  • No history of CNS disease
  • No seizure within 1 week of presentation
• Physical Exam
  • No altered level of consciousness
    • Ability to answer two consecutive questions successfully
    • Ability to follow two consecutive commands successfully
  • Normal neurologic exam

If none of the above, chance of normal ct is 97%; none of the patients herniated

CT findings that prohibit LP:

• Midline shift
  • Unequal pressures between the 3 cerebral compartments (left/right supretentorial compartments, posterior fossa)
  • Intracerebral masses not causing midline shift
• Obstructive Hydrocephalus
  • Enlargement of ventricles prox to lesions and normal ventricles distal (especially 4th ventricle)
• Basilar cisterns compressed
  • Lateral/3rd ventricles may be small due to diffuse cerebral edema or enlarged due to obstr. hydroceph. +/- shift
• Posterior fossa mass
  • Displacement/compression of 4th ventricle

Procedure

1. Sterile prep L3-L4 and L4-L5 interspaces; prepare and confirm correct tubes in numerical order
   • U/S can be used to ID interspaces in obese patients increasing your accuracy as much as 2.3 times
2. Positioning
   • Pt on side: able to measure opening pressure
   • Pt sitting: helpful for difficult habitus, but must move pt to measure opening pressure
3. Needle selection
   • 3.5 in atraumatic 22ga needle is ideal
   • Needle >20ga almost doubles incidence of post-LP headache
4. Anesthetize both superficial skin as well as along intended path of LP needle
5. Insert needle with bevel parallel to spinal canal
6. Opening pressure should be measured with pt on side with legs extended
7. Collect 1mL of CSF in each tube

CSF Studies

Standard

• Tube 1: Gram Stain and culture
• Tube 2: Protein and glucose
• Tube 3: Cell count w diff
• Tube 4: Hold

Additional

• Cryptoccal ag
• India ink
• AFB PCR
• RPR, VRDL
• Fungal cx
• viral cx
• Herpes PCR
• LDH
  • >40 suggests bacterial meningitis
  • <40 suggests viral

Diagnostic Evaluation

Measure	Normal	Bacterial	Aseptic (Viral)	Fungal	Tuberculosis	Subarachnoid hemorrhage	Neoplastic
Appearance	Clear	Clear, cloudy, or purulent	Clear	Clear or opaque	Clear or opaque	Xanthochromia, bloody, or clear	Clear or opaque
Opening Pressure (cm H2O)	10-20	>25	Normal or elevated	>25	>25	>25	Normal or elevated
WBC Count^ (cells/µL)	0-5^	>100^	5-1000	<500	50-500	0-5 (see correction section)	<500
% PMNs		>80-90%	1-50%^^	1-50%	Early PMN then lymph		1-50%
Glucose	>60% of serum glucose	Low	Normal	Low	Low	Normal	Normal
Protein^^^ (mg/dL)	< 45	Elevated	Elevated	Elevated	Elevated	Elevated	>200
Gram Stain	Neg	Pos	Neg	India ink	Tb stain	Blood

• ^Normal or lower WBC results may be found in immunocompromised, early, or partially treated (e.g. with oral antibiotics) bacterial menintigis, and those with tuberculosis meningitis
• ^^Lymph predominance may be found in patients with early bacterial meningitis or those that have been partially treated (e.g. with oral antibiotics)
• ^^^For unexplained elevations of protein, consider encephalitis, MS, Guillian Barre

Corrections

• WBC correction (for bloody tap)
  • Simplified version (if peripheral WBC and RBC counts are within normal limits):
    • Subtract 1 WBC for every 750 RBC in CSF
  • Complex version (WBC and/or RBC not within normal limits):
    • "WBCs added" = WBC(blood) x [RBC(CSF) / RBC(blood)]
    • WBC counted/resulted - "WBCs added" = actual WBC
• Protein correction (for bloody tap)
  • For each 1000 RBC decrease protein value by 1mg/dl

Complications

• Post-Lumbar Puncture Headache
• Spinal epidural hematoma

External Links

• Straus, S. et al. How Do I Perform a Lumbar Puncture and Analyze the Results to Diagnose Bacterial Meningitis?

See Also

• Meningitis
• CT Before Lumbar Puncture