Lumbar puncture

Lumbar punctures (LP) are a commonly performed hospital procedure in which a needle is inserted through the back to the subarachnoid space in the spinal canal, often to collect cerebrospinal fluid (CSF) or inject a therapeutic agent. The procedure can be performed blind via landmarks or under imaging guidance, e.g. fluoroscopy, CT or ultrasound-guided. In many locations, imaging-guided lumbar punctures are increasingly the norm ³.

Indications

• CSF sampling, e.g. for suspected meningitis or encephalitis, subarachnoid hemorrhage, CNS malignancy, neurodegenerative disease ^8,9

• opening pressure measurements ⁸

• large volume taps (30-40 mL) can be performed as a diagnostic procedure to assess short-term relief of symptoms of normal pressure hydrocephalus prior to VP shunting ⁹

• administration of intrathecal chemotherapy

• administration of contrast, e.g. CT myelography, nuclear medicine CSF leak studies ^1,4

Contraindications

• severe bleeding disorders, extreme thrombocytopenia ⁸

• suspected epidural abscess or soft tissue infection at the puncture site or expected needle course ⁸

• (congenital) deformation ⁸ of or trauma to the lumbar vertebrae

• brain tumor, abscess, or other lesions that cause elevated intracranial pressure

• Chiari malformation ⁸

Procedure

Preprocedural evaluation

Due to the possibility of brain herniation in patients with elevated intracranial pressure, many clinicians will order a head CT before the procedure. Different medical societies have varying recommendations about this issue, however, focal neurological findings or altered level of consciousness should prompt consideration of this complication.

Equipment

• sterile drapes, gloves, and dressing

• face mask is generally advised to avoid iatrogenic infection ^8,9

• antiseptic solution with skin swabs

• local anesthetic, e.g. lidocaine 1% without epinephrine

• syringe: 3 mL and 10 mL

• hypodermic needle: 25 gauge

• spinal needles

  • 22 gauge (for diagnostic lumbar punctures, opening pressures) or 25 gauge (for myelography or other injections) ^6,8

  • atraumatic/pencil-point spinal needles (e.g. Whitacre) when compared to conventional/cutting spinal needles (e.g. Quincke) have reduced rates of post-dural puncture headache, need for epidural blood patch, nerve root irritation, low back pain, nausea/vomiting ^5,8

  • conventional/cutting spinal needles may be appropriate in elderly and/or obese patients, or where the procedure is expected to be difficult ⁹

• three-way stopcock

• manometer

• three plastic test tubes with caps: numbered 1-3

  • at least 10 mL CSF is recommended to be collected ⁹, and extra test tubes may be utilized if necessary

• pulse oximetry +/- ECG leads and other monitoring devices if sedation is required or in seriously ill patients

Technique

The basic equipment for the procedure should be gathered beforehand and may include needles, specimen bottles and tubes, and manometers.

Blind

Blind lumbar punctures are usually performed with patients in a decubitus position with their knees bent towards their chest. Aseptic technique is mandatory. Local anesthesia can be given. With manual palpation, the performer identifies L3, L4, and L5, then guides a needle through the opening between the vertebrae.

Image-guided

• fluoroscopy-guided lumbar puncture

• CT-guided lumbar puncture

• ultrasound-guided lumbar puncture

Postprocedural care

• supine bed rest is commonly advised for a number of hours but bed rest itself does not affect the prevalence of post-dural puncture headache or post-lumbar puncture back pain ⁸

• pain score assessed immediately and 15-20 minutes post procedure

• observe for 20-30 minutes for any immediate complications

Complications

Complications associated with lumbar puncture occur rarely. However, minor and major complications can occur even when good technique and standard infection control measures are used.

More common complications include:

• non-specific headache: ~20% ⁸

• post-dural puncture headache: ~20% incidence ⁷

• back pain: ~17% and associated with increased number of attempts ⁸

• minor neurologic symptoms, e.g. transient pain/numbness/paralysis

• dry tap: unable to obtain CSF despite appropriate needle tip position in the thecal sac ¹⁰

Less common (<0.01%) complications include ⁸:

• infection, e.g. epidural abscess

• spinal or cerebral subdural hematoma

• seizure

• cerebral herniation (rare)

• late onset of epidermoid cysts of the thecal sac