Adult Lumbar Puncture (LP) Procedure for Diagnostic Testing

Adult Lumbar Puncture (LP) Procedure for Diagnostic Testing 

Indications 

For diagnosis of:  Subarachnoid hemorrhage, Meningitis, Neurological disorders, Cerebral lymphoma / metastatic disease 

Contra indications 

Bleeding disorders (e.g. PT > 1.3, Platelet count < 80,000), recent heparin, LMWH or other anticoagulant 

 Local sepsis such as cellulitis or abscess on back 

 Raised intracranial pressure 

 Note indications for CT scan prior to LP above 

 Previous back surgery (relative) 

 Prior history of back pain / pathology (relative) 

In certain conditions, a brain CT has to be done first before an LP is performed: 

 Immunocompromised patients 

  Recent history of head trauma 

  Impaired level of consciousness 

  Evidence of papilledema or focal neurological deficits

 If a lumbar puncture (LP) is delayed to conduct neuroimaging studies, empirical antibiotic therapy should begin after obtaining blood cultures. It is crucial to perform the LP, if there are no contraindications, and start antibiotics as soon as possible in a patient with suspected meningitis, as the outcome is dependent on the timeliness of the treatment initiation.

Supplies needed

 LP kit 

 Includes 23 g 9cm spinal needle 

 Mask, gown, gloves 

 Assistants- to hold the patient in position and to hand equipment to the operator

Consent 

Patient consent must be secured, and the procedure should be thoroughly explained to them. Major complications can involve post-dural puncture headaches, while significant back pain is rare.

 Operator (the person doing the LP)

Follow your hospital's GME policy for residents performing LP. In some city hospitals a resident has to complete 3 to 5 successful LPs with an attending doctor present. 

Patient position 

For right-handed practitioners, patients should be positioned on their left side, though a sitting position is also an option. In the sitting position, patients should sit at the edge of the bed or trolley with their legs hanging over the side. An assistant can help support the patient. Placing a pillow on the patient's lap can be beneficial, with the patient leaning forward over it.

Lumbar Puncture Procedure

The operator should wear a surgical mask, gown, and gloves after performing a surgical scrub. The patient's back should be prepared with Betadine or a similar antiseptic and allowed to dry.

Once the skin preparation is dry, the area should be covered using the plastic drape that comes with the kit, or alternatively, sterile sheets can be used to demarcate the prepared area.

The L3/4 interspace is identified using the intercristal line as a surface marker (the line at the level of the iliac crests). The spinal cord typically ends at the lower border of L1; lumbar punctures should be performed below this level.

A small amount of local anesthetic is injected into the skin and subcutaneous tissues. A 23-gauge spinal needle with a stylet is then inserted perpendicular to all planes at the L3/4 interspace and advanced into the subarachnoid space, which can be felt as a slight pop. 

The depth to the space is approximately 5 cm but can range from 3 cm to 9 cm in larger patients. If bone is encountered, withdraw the needle almost to the skin and try another approach, either more cephalad or caudad. Do not force the needle, as it can bend or fracture. Replace the stylet with each advancement of the needle. If there are three unsuccessful attempts, the operator should seek assistance. 

Remove the stylet and check for CSF flow. If CSF is present, use the manometer to measure opening pressure, considering the patient's position during interpretation. I possible, opening pressure should be measured. It is usually elevated in cases of bacterial or cryptococcal meningitis. 

Collect the initial CSF that emerges into the first tube and continue to collect CSF into pre-numbered tubes in the correct order. After collection, remove the needle and apply an appropriate dressing. Many emergency department texts recommend replacing the stylet before removing the needle. Ensure the needle is complete and intact after removal.

Cerebrospinal Fluid Collection Tubes

Tube one, which is potentially the most contaminated and blood-stained, is sent to biochemistry. Tube two is sent to cytology, and tube three, the least likely to be contaminated or blood-stained, is sent to microbiology. By keeping this in mind, it may be possible to collect additional CSF in certain tubes based on the clinical presentation. For example, in an adult with suspected meningitis:

 Always collect CSF into the tubes in the correct order (i.e. tube 1 first; tube 3 last). Some facilities require a 4rth tube to be collected which is used for comparison if result of any of the 3 other tubes need to be confirmed rather than sticking the patient again. 

(Note: Always follow your facility's policy and procedure on lumbar puncture for diagnostic tests.)