Lumbar Puncture

INTRODUCTION

• Lumbar puncture and analysis of cerebrospinal fluid is widely used as a diagnostic tool in neurological diseases.
• Lumbar puncture (LP) is the insertion of a needle into the subarachnoid space in the lumbar region to obtain cerebrospinal fluid (CSF) for diagnostic or therapeutic purposes.
• The CSF obtained by LP can provide crucial data in the diagnosis of life threatening conditions such as meningitis and encephalitis and evaluation of other disease conditions such as demyelinating diseases.
• Lumbar puncture is alsoperformed for therapeutic reasons, such as the treatment of benign intracranial hypertension. 
•  The spinal cord ends at the lower border of L1 vertebrae (Fig 1).
• Below this are nerve roots – the cauda equina. Lumbar puncture can be safely done below L1-2 vertebral space, as there is no risk of injuring the spinal cord.

Indications for Lumbar Punctur

Diagnostic

1.       Suspected meningitis or encephalitis

2.       Suspected subarachnoid haemorrhage  with a normal CT scan

3.       Neoplasia – diagnostic cells may be found in patients with leukemia or carcinomatous meningitis.

4.       Diagnosis of Guillain-Barré syndrome and  multiple sclerosis

5.       To obtain pressure measurements

6.       Diagnostic imaging  such as CT myelograme 

Therapeutic

1.       Spinal anesthesia: intrathecal or epidural.

2.       Chemotherapy: drugs may be administered via the epidural or spinal route.

3.       Removal of CSF:  benign intracranial  hypertension 

Contraindications for Lumbar Puncture

1.       Suspicion  of  intracranial space occupying lesion

2.       Suspicion of a compressive lesion in the spinal cord

3.       Infection near the site of needle  insertion

4.       Bleeding diathesis; thrombocytopenia, haemophilia and warfarin therapy

5.       Evidence of raised intracranial pressure and or focal neurological signs.

Presence of  papilloedema, focal neurological signs or diminished level of consciousness mandate a CT  scan of  head scan prior to lumbar puncture.

The need to perform a CT scan should not delay the administration of antibiotics if meningitis is suspected

PROCEDURE

Materials

·         Sterile gloves.

·         Antiseptic solution (iodine in alcohol or clohexadine ) .

·         Spinal needle (atraumatic needle 20-gage needle in adults, 22-gage or smaller in children).

·         4 specimen tubes  labeled from 1-4.

·         Local anesthetic solution and needles.

·         Sterile drapes.

Method

Steps

1. Written informed consent
2. Position: - lateral decubitus  or seated positions.
3. The site for needle insertion
4. Sterile preparation and draping
5. Local skin infiltration
6. Insertion of the spinal needle
7. Collection of fluid
8. Measure RBS immediately after the procedure 

Step 1: Written informed consent

·         Communicate clearly to explain the procedure to the patient and the family members.

·         Explain to patient what you want to do, and why you need to do it.

·         Explain that you will give a local anaesthetic, which will involve a sharp scratch and then there will be no pain during the procedure.

·         Discuss briefly possible complications such as headache.

·         Give patient an opportunity to ask questions.

·         Obtain written informed consent.

Step2: Position the patient

Position the patient comfortably either in the left lateral position or the sitting position  (Fig    2).

Left  lateral  position:

• Flex the back as far as possible.
• Ask the patient to try to touch the flexed  knees with his/her chin.
• Place one pillow under the head and one between the knees for support.
• Neck should be maximally flexed.
• The back should be at right angles to the floor with one hip exactly above the other.

Sitting position:

·         The patient is seated with the neck and back fully flexed.

·         Flexion facilitates the course of the needle through the widened gaps between adjacent lumbar spinous processes.

Step 3: Determine the site of needle insertion

Identify landmarks ; iliac crest (L4) and  vertebral spinous processes (Figure 3).

A line joining the posterior superior iliac crests will intersect the midline at L4/L5 interspace. The needle is inserted between L3/L4 or L4/L5 space.

Both these spaces are below the termination of the spinal cord at L1/L2 in the majority of adults.

 

Difficulty in finding landmarks may be experienced in obese patients , patients with osteoarthritis – osteophytes may impede access to the spinal canal, ankylosing spondylitis and  kyphoscoliosis

Step 4: Sterile preparation and drapin

• Wash hands and put on a mask, sterile gown and sterile gloves.
• Swab the area around the insertion site with iodine in alcohol or clohexadine  in a circular movement outwards from the proposed puncture site.
• Drape the area with sterile cloths.

Step 5: Insertion of the spinal needle:

• Anesthetize the skin and subcutaneous tissue using the 1% lignocaine in a 5 mL syringe with the 25-gauge needle.
• The needle is inserted between L3/L4 or L4/L5 space.
• Use the index and thumb to hold the skin taut and insert the LP needle  in the midline with the needle parallel to the floor and the point directed slightly towards the patient's umbilicus. 
• Advance slowly feeling the resistance from spinal ligaments and then dura. With further advancement of the needle, subarachnoid space is identified by a give in the resistance of tissues.
•  Remove the stylet within the needle to find a flow of CSF which is clear and colorless.

What you go through on the way to the subarachnoid space Skin Subcutaneous tissaue Supraspinous ligament Ligamentum flavum- feel a ‘pop’ as it is penetrated Epidural space Dura and arachnoid Subarachnoid space (CSF)

If the needle meets the bone ( hard feeling with difficulty in advancing the needle) or if blood returns (hitting the venous plexus anterior to the spinal canal), withdraw to the skin and redirect the needle.

If CSF return cannot be obtained, try one disk space down.

Step 6: Collection of fluid

·   Take the stylet out when the needle is properly placed. The CSF should be clear with a slow flow.
·    If the flow is very slow rotate the needle 90 degrees to clear the opening at the end of the needle as it may be obstructed by a nerve root.
·    To  measure  the CSF pressure connect the manometer to the needle hub. Keep the manometer perpendicular to the patient. Open the tap to allow CSF to flow up the tube and wait until the CSF column is stable to take the reading. Normal pressure 80 – 180 mm of water.
·   Remove the manometer and collect 1 to 2 ml of CSF each of the three numbered sterile tubes.
·   Send the first for glucose and protein, the second for Gram stain, culture and sensitivity and AFB , and the third tube for cell count. 
·    A fourth tube, may be collected and kept for further investigations if needed.
·    Draw a 2 ml of venous blood for random blood sugar measurement.

    NEVER…

…have more than 3 attempts in any single interspace before either obtaining assistance from a  senior colleague or proceeding to another interspace.

…try to aspirate CSF. This may have serious neurological consequences.

Step 7: Removal of the spinal needle

• Reinserting the stylet before needle removal helps prevent post spinal headache. This reduces the risk that a frond of arachnoid will be pulled out and prevent closure of the dural puncture defect.
• Apply pressure over the puncture site and then cover with a sterile dressing.

 Dry tap

• A dry tap is usually due to incorrect positioning of the patient and misdirection of the needle.  Re-maneouver is necessary if bony resistance is encountered or if no CSF emerges.
•  If firm resistance is encountered, do not force the needle - it may be against the bone or an intervertebral disc.
• Low pressure may indicate that flow in the spinal canal is impaired. This is seen in spinal lesions or  with cerebellar tonsillar impaction.
• No attempt should ever be made to aspirate CSF as this may cause neurological damage.

Complications of Lumbar Puncture

1.       Traumatic tap

Traumatic tap is defined as a fluid containing macroscopic blood. This may be due to too lateral placement of the needle involving the posterior external vertebral venous plexus in the epidural space.

Traumatic tap should be distinguished from a subarachnoid hemorrhage.  Fluid usually clears between first and third collections in a traumatic tap whereas in subarachnoid bleeding it is mixed evenly in all 3 tubes.

2.        Headache

This is  the most common complication. It is usually due to leakage of CSF through the dural puncture site into the epidural and paravertebral spaces. It usually starts 48 hours after the procedure and may last up to 1 to 2 days and even two weeks.

Prevention of headache

·         The smaller the needle used for the lumbar puncture, the lower the risk of a headache. The smallest possible atraumatic needle with a stylet should be used.

·         Avoid multiple punctures.

·         Maintain adequate hydration during post procedure.

3.       Herniation syndromes

Large pressure gradients exist between the cranial and lumbar compartment in supratentorial mass lesions.  By performing a lumbar puncture, the pressure in the spinal compartment may be lowered and transtentorial and foramen magnum herniation may occur.

Signs and symptoms indicating this are pupillary and occulomotor fixation, quadriparesis, posturing and changes in respiration.

Prevention:

A careful history and neurological examination should precede any lumbar puncture. If there is any suspicion of raised intracranial pressure a CT scan is mandatory before the procedure.

4.       Pain referred to the lower limb

A shooting pain down a leg during the procedure indicates that a nerve may have been hit.   

Withdraw the needle completely and start again.

5.       Seedling of infection to meninges

6.       Subdural hematoma - In elderly people, the removal of a large volume of CSF may result in a tear or avulsion of a perforating vein.

7.       Backache

Transient sensory symptoms due to irritation of individual nerve roots of the cauda equina are common and present as a shooting pain.

6.       Routine Evaluation of CSF

·         Cell count and differential cell count

·         Glucose and protein level

·         Gram stain, culture and sensitivity

·         Staining for AFB

·         Other investigations

                            VDRL and Cryptococcal antigen,

                            TB culture,

                            Cytology,

                            HSV-PCR when indicated.

CSF Changes in Meningitis

	Normal	Viral	Pyogenic	Tuberculosis
Appearance   Lymphocytes   Polymorphs   Protein   Glucose	Clear   <5 mm3   Nil   0.2-0.4 g/L   2/3 blood glucose	Clear/Turbid   10-100mm3   Nil   0.4-0.8 g/L   >1/2blood glucose	Turbid/purulent   <50 mm3   200-300 /mm3   0.5-2.0 g/L   <1/2 blood glucose	Turbid   100-300 mm3   0-200mm3   0.5-3.0 g/L   <1/2 blood glucose