Lumbar Punctures

Question 1

Indications for an LP?

Answer 1

To Diagnose:

• Meningitis/Meningoencephalitis
• Subarachnoid Haemorrhage
• Malignancy (diagnose & Treat)
• Idiopathic Intracranial Hypertension
• Detect Oligoclonal bands to indicate CNS inflammation e.g. MS

To infuse drugs or contrast

Question 2

Contraindications for a LP?

Answer 2

• Patient has CV or Resp Instability
• Infection in skin or soft tissue over puncture site
• Unstable bleeding disorder (Diagnosed, low platelets or low clotting factors)
• Raised ICP (CT first to spot a mass which may herniate)

Question 3

What are the types of LP needle?

Answer 3

• Spinal needles usually 22 gauge

- Atraumatic needles (Cause less spinal headaches but cost more)

Question 4

What is used to anaesthetize for an LP?

Answer 4

Topical anaesthetic to injection site such as EMLA

OR lidocaine inserted intradermally, then carried through on needle

Question 5

In what position is an LP performed?

Answer 5

Lateral (Decubitus) position:
- Lying on left side with maximally flexed spine (particularly at hips)

Sitting (Infants):
- Infants hands held between its flexed legs using one hand and the other hand flexes its head

Question 6

What vertebral level is an LP performed?

Answer 6

L3-4 in adults and L4-5 in infants

Question 7

Procedure for an LP:

Answer 7

• ~Anaesthetize topically 30 mins before
• Adopt position
• Clean skin with Povidone Iodine to 10cm from puncture site and allow to dry
• Drape below patient and around site
• ~Anaesthetize with lidocaine
• Insert spinal needle + Stylet with bevel upwards (parallel to spinal cord)
• Aim Cephalad to get through slanted lamina
• Pop of sudden lack of resistance means your in, remove stylet and collect CSF

Question 8

What do you do if theres no fluid?

Answer 8

• Rotate the needle 90 degrees
• Reinsert stylet and advance needle again
• Compress jugular

Question 9

How is CSF pressure measured?

Answer 9

With a Manometer in the lateral position only, once CSF starts to flow

Question 10

How much CSF do you collect on an LP?

Answer 10

3 vials as standard:

• Culture & gram stain
• Glucose & Protein
• Cell count & DDx

Question 11

How is the LP ended?

Answer 11

Measure closing pressure with manometer if you want

• > Reinsert Stylet
• > Smoothly remove needle
• > Cleanse and cover puncture site

Question 12

What is the Paramedian or Lateral Approach?

Answer 12

Approaching the spine at an angle not quite in the midline (10-15 degrees out)
This passes through the erector spinae & Ligamentum flavum rather than Supraspinal/interspinal ligaments

Helps in patient with calcifications, anatomical abnormalities or just to reduce Spinal Headaches (hole through dura&arachnoid wont overlap)

Question 13

Complications of a LP?

Answer 13

• Headache
• Apnea
• Back Pain
• Bleeding or leaking
• Infection or Haematoma
• Subarachnoid Epidermal cyst (Carried Skin cells through to meninges)
• Nerve Trauma
• Ocular Muscle Palsy
• Brainstem Herniation

Question 14

Describe spinal headache?

Answer 14

A common complication of LPs
More likely in women, young people, low BMIs and people with a history of headaches

Its bilateral and improves with lying down

Question 15

How do we treat a spinal hedache?

Answer 15

It will last hours to weeks

We can help with:

• Hydration
• Caffeine (PO/IV)
• Epidural Blood Patch to stimulate healing

Question 16

How do we prevent a spinal headache?

Answer 16

1) Keep needle bevel parallel to spinal cord to minimise tearing
2) Replace stylet before removing needle
3) Use small diameter or atraumatic needles

Question 17

How would a nerve root trauma complication present in an LP and what do you do if you cause it?

Answer 17

Sudden electric shocks of dysaesthesia

Its rarely permanent

You should withdraw immediately

If the pain or weakness is persistant you may have caused irritation warranting CCSs

After that Nerve conduction studies and EMG may be necessary to investigate further

Question 18

How does a herniated brainstem appear when caused by LP?

Answer 18

Altered mental status -> Cranial nerve abnormalities -> Cushing’s Triad
It can often be rapidly fatal

You must:

• Remove needle
• Raise head of bed to drain venous blood
• 3% saline (hypertonic so draws fluid into blood, reducing ICP)
• Intubate & Hyperventilate
• Call neurosurgeon

Question 19

What options are there should your LP fail?

Answer 19

• Get someone else
• Radiographic guided LP with US, Fluoroscopy or CT
• Cisterna Magna Tap (C1/2)

Question 20

Describe the results from a normal LP?

Answer 20

• Clear & Colourless
• Opening pressure 6-16 mm Hg
• 35 mg protein
• 60% glucose as in blood
• WCC<5

Question 21

What should you do when sending CSF to the lab?

Answer 21

Send with Blood sample to compare glucose

Put it in a brown envelope or the sunlight damages the sample and they all come back diagnosed with SAH