Indications for an LP?
- Subarachnoid Haemorrhage
- Malignancy (diagnose & Treat)
- Idiopathic Intracranial Hypertension
- Detect Oligoclonal bands to indicate CNS inflammation e.g. MS
To infuse drugs or contrast
Contraindications for a LP?
- 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)
What are the types of LP needle?
- Spinal needles usually 22 gauge
- Atraumatic needles (Cause less spinal headaches but cost more)
What is used to anaesthetize for an LP?
Topical anaesthetic to injection site such as EMLA
OR lidocaine inserted intradermally, then carried through on needle
In what position is an LP performed?
Lateral (Decubitus) position:
- Lying on left side with maximally flexed spine (particularly at hips)
- Infants hands held between its flexed legs using one hand and the other hand flexes its head
What vertebral level is an LP performed?
L3-4 in adults and L4-5 in infants
Procedure for an LP:
- ~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
What do you do if theres no fluid?
- Rotate the needle 90 degrees
- Reinsert stylet and advance needle again
- Compress jugular
How is CSF pressure measured?
With a Manometer in the lateral position only, once CSF starts to flow
How much CSF do you collect on an LP?
3 vials as standard:
- Culture & gram stain
- Glucose & Protein
- Cell count & DDx
How is the LP ended?
Measure closing pressure with manometer if you want
- > Reinsert Stylet
- > Smoothly remove needle
- > Cleanse and cover puncture site
What is the Paramedian or Lateral Approach?
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)
Complications of a LP?
- Back Pain
- Bleeding or leaking
- Infection or Haematoma
- Subarachnoid Epidermal cyst (Carried Skin cells through to meninges)
- Nerve Trauma
- Ocular Muscle Palsy
- Brainstem Herniation
Describe spinal headache?
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
How do we treat a spinal hedache?
It will last hours to weeks
We can help with:
- Caffeine (PO/IV)
- Epidural Blood Patch to stimulate healing
How do we prevent a spinal headache?
1) Keep needle bevel parallel to spinal cord to minimise tearing
2) Replace stylet before removing needle
3) Use small diameter or atraumatic needles
How would a nerve root trauma complication present in an LP and what do you do if you cause it?
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
How does a herniated brainstem appear when caused by LP?
Altered mental status -> Cranial nerve abnormalities -> Cushing’s Triad
It can often be rapidly fatal
- Remove needle
- Raise head of bed to drain venous blood
- 3% saline (hypertonic so draws fluid into blood, reducing ICP)
- Intubate & Hyperventilate
- Call neurosurgeon
What options are there should your LP fail?
- Get someone else
- Radiographic guided LP with US, Fluoroscopy or CT
- Cisterna Magna Tap (C1/2)
Describe the results from a normal LP?
- Clear & Colourless
- Opening pressure 6-16 mm Hg
- 35 mg protein
- 60% glucose as in blood
What should you do when sending CSF to the lab?
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