Week 3-Lumbar puncture, epidural, spinal and caudal

Question 1

What are the indications for a lumbar puncture?

Answer 1

Diagnosis of:

meningitis/ encephalitis

subarachnoid haemorrhage (in patient with normal CT)

measurement of CSF pressure

removal of CSF therapeutically (idiopathic cranial hypertension)

diagnosis of MS/ neurosyphilis

intrathecal injections and drugs

Question 2

What are the normal parameters of CSF?

Answer 2

normal parameters of CSF:

appearance –> crystal clear, colourless

pressure –> 8-15 mmHg

cell count –> no polymorphs, mononuclear cells only, less than 5/mm3

protein 0.2-0.4 g/L

Glucose 2/3 - 1/2 of blood glucose

IgG –> less than 15% totatl CSF protein

oligoclonal bands –> absent

Question 3

What are the contraindications to LP?

Answer 3

• Patient refusal
• Raised intracranial pressure –> papilloedema via fundoscopy, bulging optic disc and engorged veins
• Regional skin/ soft tissue infection
• cord compression
• coagulopathy
• congenital malformation
• spinal fixation surgery

Question 4

How is a patient checked for raised ICP?

Question 5

What are the complications of LP?

Answer 5

Headache (common)

Bloody (traumatic) tap

Brain or cerebellar herniation

Extradural haematoma (within fat filled space with veins, bleed can track up and compress the spinal cord).

Meningitis

CN VI palsy/ hearing loss

Transient/ persistent paraesthesia/ anaesthesia

Question 6

Label image

What should you be careful of during a LP?

Answer 6

1) Vertebral body
2) vertebral disc –> nucleus pulposus, annulus fibrosis
3) pedicle (directly posterior to vertebral body)
4) spinous process
5) Transverse process

Ligaments (from outside to in):

1) supraspinous ligament
2) interspinous ligament
3) ligamentum flavum (elastic, yellow coloured)

Need to be careful not to puncture too far through the ligamentum flavum and not to hit the intervertebral disc –> could increase risk of disc herniation and pain for the pt.

Question 7

Where does the spinal cord terminate?

What level is lumbar puncture done at?

Answer 7

Spinal cord terminates at L1/L2

Lumbar puncture is done normally at L3/L4 (although can be done at L4/L5, L5/S1 as there is still CSF) to avoid the end of the spinal cord (conus medullaris). The cauda equina nerves tend to move out the way of the needle.

Question 8

Where does the CSF filled sub arachnoid space terminate in most people?

What is the range of this?

What can the termination of subarachnoid space be landmarked by?

Answer 8

CSF filled subcarachnoid space terminates in 90% of adults from the lower part of S1-S2 level

(ranges from L5-S1 to S4).

Termination of the subarachnoid space can be landmarked using the PSIS and sacral spinous processes.

Question 9

Label the image -> what are the meningeal layers and spaces inbetween?

what are the contents of these spaces?

Answer 9

Spinal cord is immediately surrounded by the pia mater

Outside the pia mater is the subarachnoid space (filled with CSF and connective tissue trabeculae)

Around the subarachnoid space is the arachnoid mater

outside the arachnoid mater is the subdural space with traversing cerebral bridging veins, draining the neural tissue into the dural sinuses (potential space, can be opened by separation of arachnoid mater from the dura mater by result of trauma, pathologic process, or the absence of cerebrospinal fluid as seen in a cadaver)

outside the subdural space is the dura mater

outside the dura mater is the epidural space filled with adipose tissue and the vertebral venous plexus

Question 10

What structures do you need to be careful of during LP?

Answer 10

Spinal nerves leave the spinal cord laterally, you need to be careful not to impact a spinal nerve as you enter the needle.

Question 11

What are the vertebral levels related to these two points?

Answer 11

Question 12

What does the cauda equina consist of?

What space does it occupy?

Answer 12

Cauda equina consists of nerves and nerve rootlets from:

L2-L5

S1-S5

coccygeal nerve

Cauda equina occupies the lumbar cistern, the subarachnoid space inferior to the conus medullaris

Question 13

Is this slice above or below L1?

Would a LP be done here?

How can you tell? (label as many features as poss)

Answer 13

This slice is above the level of L1 as the spinal cord is still present.

Immediately surrounding the spinal cord are the meningeal layers, the red line consisting of both the arachnoid and dura mater.

Outside the dura mater is the epidural space filled with fat and venous plexus (the dark fragments)

Either side of the spinal cord you can see two spinal nerves exiting

In front of the spinal cord you can see the large vertebral body and a slice through the vertebral disc (with annulus fibrosus and nucleus pulpolsus).

Posteriorly you can see the spinous process and transverse processes of the lumbar vertebrae.

Question 14

What does 1) the white zone represent?

What does 2) the red zone show?

Answer 14

Zone 1 –> white box shows the zone of spinal cord termination which can extend from the middle 1/3rd of T11 to the middle 1/3rd of L3

Zone 2 –> red box shows the most common level of spinal cord termination –> at the middle 1/3rd of the L1 vertebral body which corresponds with the interspinous space between T12 and L1 spinoous process (at spinous processes are angled downwards).

Question 15

What are zones 3 and 4?

Why might doing a spinal tap in zone 3 potentially cause a problem?

Answer 15

Zone 4 –> is the highest point of the iliac crest and the supracristal plane; it intersects the vertebral column from L4 to the the L4/L5 intervertebral disc (in majority of pts).

Find L4 to do your LP, however the zone that palpation directs you to may vary between clinicians, plus anatomical variation between patients leads to zone 3:

Zone of supracristal plane intersection with the vertebral column

Can range from L2-L3 to the L4/L5 interspinous space –> this could potentially cause a problem in a patient with a low terminating cord (at L3). Therefore advice is to always go a vertebral level lower.

Question 16

What is the yellow part of the spinal cord shown? What spinal nerves arise here? What vertebral level?

Answer 16

The yellow part of the spinal cord = lumbar part

Lumbar spinal nerves arise here, L1-L5, origin actually at T12 vertebral level.

Question 17

What nerves are the orange part of the spinal cord shown?

What vertebral level is this part of the spinal cord located at?

Answer 17

The orange part of the spinal cord is the sacral part, sacral nerves can be followed exiting sacral foramina.

The sacral portion of the spinal cord can actually be located at L1/L2 (S1-S5 spinal nerves originate here).

Question 18

What is the range of vertebral levels at which is is acceptable to do LP in and adult?

How does this change in a child?

Answer 18

In adults LP is performed via the L3-L4 to L5-S1 interspinous gap

Preference at L4/L5 vertebral level.

In children and neonates –> lumbar puncture is performed at the L4/L5 of L5-S1 interspinous gap.

This is because the infanct spinal cord terminates at the L3 level

Question 19

Where is a needle inserted during an LP?

What way should the needle be angled?

Without this angulation what could be hit?

Answer 19

The needle is inserted between spinous processes and is angled anterosuperiorly (15 degrees cephalad orientation, aim towards umbilicus).

Without antero superior angulation, the needle will hit the bone, usually the lamina.

Question 20

What position should the patient be in during the LP and why?

Answer 20

During LP patient is either on their side or sat on the bed hunched forwards to flex the vertebral column, legs to chest.

This increases the space inbetween the adjacent spinous processes making it easier to insert the needle.

If done on neonates or unconcious patients another person is required to help position them with their vertebral column flexed.

Question 21

Why/ when might a patient’s O2 sats need monitoring during a LP?

Answer 21

During an LP when a patient is hunched over/ lying down you may reduce tidal volume.

This shouldn’t be problematic in normal patients but in obese patients/ elderly/ patients with comorbidities they can become hypoxic.

Question 22

What layers are passed through during an LP?

Answer 22

1) Skin and subcutaneous tissue
2) Supraspinous ligament (will feel resistance)
3) interspinous ligament
4) Ligamentum flavum –> feel a loss of resistance/ “give” when passed through

Question 23

what does the supraspinous ligament become in the cervical region?

Why is this structure surgically useful?

Answer 23

supraspinous ligament becomes the ligamentum nuchae in the cervical region.

Ligamentum nuchae is avascular and aneural, useful for cervical procedures.

Question 24

What must the needle penetrate (apart from skin/ subcut fat) to reach the subarachnoid space?

When is a loss of resistance/ pop felt?

What space has been entered?

When might another loss of resistance be felt?

What space has been entered?

Answer 24

The needle must penetrate ligamentum flavum, the dura and arachnoid mater to reach the CSF.

Distinct loss of resistance may be felt when needle penetrates ligamentum flavum and enters the epidural space.

Another loss of resistance may be felt as the needle penetrates the dura and arachnoid mater. Now entered the subarachnoid space.

Question 25

What is the epidural space filled with? how far does it sit from the skin? How thick is the epidural space?

Answer 25

Epidural space is filled with fat (of varying thickeness) and veins. The soace sits 4.5-5.5 cm from the skin in the lumbar region. The epidural space is around 7mm thick in the midline lumbar region. Thickness varies depending on region entered.

Question 26

Tips on lumbar puncture procedure?

Answer 26

Use firm bed with pt lying at right angle needle can get blocked --\> try rotating CSF should run freely and appear clear, if blood comes through try pushing the needle a little further as you may have hit a vein Collect multiple tubes

Question 27

Why might a patient get a headache after having a lumbar puncture? What can a patient be advised to do to minimise the chance of a headache?

Answer 27

* LP removes CSF out of a sealed system * The brain depresses slightly which stretches the meninges * Meninges are innervated via meningeal nerves off CN V (trigeminal nerve). * Advice --\> Patient should lie down to reduce the risk of a headache

Question 28

What can increase the risk of headache/ herniation during LP?

Answer 28

Increased risk from: Multiple punctures Needle bevel at wrong orientation Large needle

Question 29

Why might a dry tap occur during LP? What may be the cause?

Answer 29

Dry tap occurs when the subarachnoid space is not entered or the needle blocks. May have introduced the needle at the wrong angle (not down the midline), when at the wrong angle they can hit the bone and nerve root damage may occur. Potential cause --\> may be due to too little vertebral column flexion; the patient is not perpendicular to the bed

Question 30

Why does traumatic (bloody) tap occur? What makes this more likely to occur?

Answer 30

Traumatic/ bloody tap can occur when the internal vertebral venous plexus is pierced. This is more likely to occur with an increased number of attempts, or lateral deviation of the needle, as the majority of the venous plexous tends to sit laterally to the midline.

Question 31

Which direction should the bevel of the needle face when doing a LP?

Answer 31

The opening of the bevel should face the ceiling with the patient lying in the lateral decubitus position (on side). When the bevel faces the ceiling it enters parallel to the dura and splits it (less leakage of CSF, parallel fibres come back together). This reduced the risk of headache. If the bevel faces another way it cuts through the dura and its parallel fibres (more leakage of CSF, healing needs to occur). This increases the risk of headache.

Question 32

What is a major risk of LP? What types of this risk may be seen?

Answer 32

Removing CSF decreases the pressure in the vertebral canal and can result in inferior herniation of neural tissue. You essentially create a high pressure gradient between the cranium and vertebral canal --\> can lead to either cerebellar herniation via foramen magnum or tentorial herniation. (E.g. in picture on the right part of the temporal lobe has herniated via tentorium.)

Question 33

Signs and sx of a tentorial herniation?

Answer 33

Look up

Question 34

Why/ when is an epidural anaesthesia carried out?

Answer 34

Indications: look up

Question 35

Where can an epidural anaesthesia be done? When does extra care need to be taken? What is anaesthetised?

Answer 35

Epidural anaesthesia can be done at any level of the vertebral column, however most commonly is done in the lumbar region. Extra care needs to be taken when anaesthetising cervical regions, especially regions of the origin of the phrenic nerve and cardiac autonomics. The spinal nerves leaving at this region will be anaesthetised.

Question 36

How does the needle insertion route for epidural anaesthesia differ to lumbar puncture?

Answer 36

Needle insertion is almost exactly the same except you stop in the epidural space --\> Infiltrate with local anaesthetic Introduce the needle along the midline (go through skin/ sub cut fat/ supraspinous ligament/ interspinous ligament/ ligamentum flavum) Loss of resistance (pop) felt after perforation of ligamentum flavum --\> stop here.

Question 37

How can you vary the number of spinal nerves anaesthetised?

Answer 37

The volume of anaesthetic agent can be increased to anaesthetise more spinal nerves. The larger the volume of anaesthetic used --\> multiple spinal nerves anaesthetised. To achieve up to a T10 block from an L3/L4 injection use 9-18 ml of local anaesthetic.

Question 38

How can you gain more control during an epidural procedure?

Answer 38

Question 39

How far is the epidural space from the skin in the midline?

Answer 39

In 80% of the population the epidural space is 4.5 - 5.5 cm from the skin in the midline

Question 40

How does the angle of introduction of spinal epidura vary in different regions of the vertebral column? What can happen on incorrect angling of the needle?

Answer 40

Needle needs to be angled more cephalad in the thoracic region. Using incorrect needle angulation can result in the needle contacting the bone

Question 41

Where does anaesthetic go during a spinal anaesthesia? What are the benefits?

Answer 41

Anaesthetic enters the subarachnoid space filled with CSF benefit --\> faster onset, less anaesthetic agent needed, different ways of controlling level of anaesthesia

Question 42

Where is spinal anaesthesia done? What neural structures will be bathed in anaesthetic? How can you control the level of anaesthesia?

Answer 42

Spinal anaesthesia is performed through the L3-L4 to L5-S1 interspinous space. The spinal nerves will be bathed in anaesthetic as the anaesthetic is introduced to the CSF filled subarachnoid space. You can control the level of anaesthesia by the volume and density of the anaesthetic agent and by the positioning of the pt.

Question 43

What is a combined spinal epidural?

Answer 43

Combined spinal epidural (CSE) --\> both a spinal and lumbar epidural are delivered via the same needle. Insert the needle into the subA space, introduce spinal anaesthetic, retract needle and leave the cannula in the subdural space to continue the anaesthesia Used for operative procedures and labour (caesarian/ episiotomy/ ventouse) Can be associated with more rapid cervical dilation vs epidural alone

Question 44

What is caudal epidural?

Answer 44

Caudal epidural = inhection is made into the sacral epidural space via the sacral hiatus, marked either side by sacral cornua

Question 45

Where is the sacral hiatus located?

Answer 45

The sacral hiatus is located at the inferior apex of an equilateral triangle measured between the posterior superior iliac spines.

Question 46

What is anaesthetised in a caudal epidural?

Answer 46

caudal epidural anaesthetises the sacral spinal nerves --\> used to anaesthetise the birth canal and perineum

Question 47

how does the angle of introduction of the needle change during caudal epidural?

Answer 47

Needle is introduced at an oblique angle, then directed cephalad and advanced to avoid contacting the subarachnoid space