4.2 Central Neuraxial Blocks - Epidural

Question 1

Epidural space

Where

Extends

Answer 1

Epidural space (extradural) lies

between spinal dura mater
and walls of
vertebral canal.

It extends from the
base of the skull to
the sacral hiatus.

Question 2

Epidural space

contains

Answer 2

It contains 
fat, 
lymphatics, 
areolar tissue, 
nerves and 
venous plexus.

There is no free fluid present.

Question 3

Batson’s venous plexus

Answer 3

Batson’s venous plexus, 
present in the epidural space, 
is a valveless system in continuity 
with the pelvic veins and venous system of the
abdominal and thoracic body wall.

This explains the more common
blood vessel puncture in pregnant
patients, as epidural veins

are engorged due to caval compression
(especially in paramedian insertions).

Question 4

Anterior dura v posterior nerve supply

periosteoum

flavum

Answer 4

The anterior dura is heavily
innervated by nerves,
but the posterior
dura is poorly supplied.

The periosteum is pain-sensitive but the
ligamentum flavum is not.

This allows spinal anaesthetic with little
pain.

Question 5

Posterior border of epidural space

Answer 5

The ligamentum flavum
forms the posterior
boundary of epidural space.

Question 6

Epidural in elderly /obese

Answer 6

epidural fat increases
with obesity and decreases with age.

This explains
why epidural local anaesthetic
requirement is lower in the elderly

Question 7

Spinous processes angulation

Cervical
Thoracic
Lumbar

Answer 7

Spinous processes of 
cervical, 
thoracic and 
lumbar vertebrae have
different angulation.

They are relatively straight, posteriorly directed

at
cervical, 
lower thoracic 
and 
lumbar levels.

But they are caudally inclined at thoracic levels

Question 8

Greatest degree of angulation Spinous processes

Answer 8

greatest degree of angulation is at
T3–T7,
making medial approach to
epidural space technically difficult.

Hence a paramedian
approach is easier at this level.

Question 9

Vertebral levels and landmarks

Most prominent

spine scapula

inferior angle scapula

line connecting iliac crest

line connecting post inf iliac spine

Answer 9

C7: vertebrae prominens

T3: spine of scapula

T7: inferior angle of scapula

L4: line connecting iliac crest

S2: line connecting posterior inferior iliac spine.

Question 10

Absolute contraindications epidural

Answer 10

Absolute contraindications for epidural blockade include

patient refusal, 
infection at injection site, 
allergy to local anaesthetic, 
raised intracranial pressure 
and hypovolemia.

Question 11

Relative contraindications epidural

Answer 11

Relative contraindications include
a 
platelet count < 100 000 per mL, 
hypertension, 
sepsis, 
anatomical abnormality of spine, 
previous spinal surgery 
and an uncooperative patient

Question 12

physiological effects of epidural anaesthesia

Cardiovascular Block below + Above T4:

Answer 12

physiological effects of epidural anaesthesia

Cardiovascular Block below T4:

venodilation and arterial dilation,

decrease in venous return and
systemic vascular resistance

compensatory reflex
vasoconstriction above the blockade

Block above T4:
blocks the cardio-acceleratory fibres,
resulting in bradycardia and hypotension

Question 13

physiological effects of epidural anaesthesia

Respiratory

Answer 13

Respiratory
Minimal effects on pulmonary function

Vital capacity,
tidal volume,
minute ventilation and
dead space are maintained

Forced expiratory volumes reduced

Question 14

physiological effects of epidural anaesthesia

Renal

Answer 14

Renal

Urinary retention may occur from
blockade of S2–S4 fibres

Due to renal autoregulation,
renal blood flow is maintained.

Question 15

physiological effects of epidural anaesthesia

Gastrointestinal

Answer 15

Gastrointestinal
Increase in secretions,

peristalsis and a
contracted gut occur

because of unopposed
parasympathetic action

The visceral perfusion is well maintained

Nausea from increased gastric peristalsis

Question 16

physiological effects of epidural anaesthesia

Neuroendocrine

Answer 16

Neuroendocrine

Epidural blockade abolishes the
stress response to surgery by
blocking the afferent sensory fibres

Thoracic epidural prevents an
increase in post-operative
nor-epinephrine release,

which causes vasospasm,
thus offering cardioprotective benefits

Question 17

Which epidural lower v upper abdo is more effective decreasing stress response

Answer 17

Epidural anaesthesia
more effectively decreases stress response
with lower abdominal
and lower-limb surgeries

than upper-abdominal
and thoracic surgeries.

This is because not all the nociceptive
afferent fibres in upperabdominal
and thoracic surgeries may be blocked.

Question 18

Additives to epidurals

Epinephrine

Duration

how

added benefit?

Answer 18

Epinephrine added to 
local anaesthetic solution 
(short- and medium prolongs the 
duration of action both by 
pharmacodynamic
and pharmacokinetic effect. 

Pharmacokinetic effect –
slower drug clearance from epidural space,
resulting in decrease in peak plasma
concentration,
mainly by decreasing blood flow in the dura mater.

Pharmacodynamic effect –
acts on α2 receptors,
decreasing pain
transmission.

Question 19

Additives to epidurals

Epi affect on BP

Answer 19

Epinephrine may increase the incidence of hypotension, because of
its β2 (vasodilatation) effect

Question 20

Additives to epidurals

Soda Bic

Benefit

How

Answer 20

Adding bicarbonate to 
local anaesthetic 
increases the unionised form,
hence more drug can 
penetrate the lipid membrane, thereby
increasing the speed of onset.

Question 21

Additives to epidurals

Soda Bic

Solution for ligno / ropiv

Answer 21

recommended solutions of sodium bicarbonate to be added to local
anaesthetic are 1 mEq/mL for lignocaine and other shorter-acting agents, and
0.1 mEq/mL for bupivacaine and ropivacaine.

Question 22

Site of epidural injection

What affects density

What affects height

Answer 22

Site of epidural injection is important
(should correlate with the
dermatome of surgical
incision for maximal effect).

Concentration of local anaesthetic mainly affects the density of the
block.

Volume affects the height of the block.
Usually 1–2 mL per segment
is used for epidural blockade.

Question 23

Epidural height affected by patient weight and height?

Answer 23

Weight and height have no correlation
with the spread of epidural
drug, except in extreme scenarios.

Question 24

LOR to fluid described by

What sign given

issues if use too much NaCL

Answer 24

The loss or resistance (LOR) to
fluid to identify the epidural space was
first decribed by Dogliotti.

It mainly gives a visual sign of entry into
epidural space and is not dependent on the feel.

If a large volume of
saline is used it may produce inadequate
blockade due to dilution of
local anaesthetic.

Question 25

How differentiate fluid from catheter csf v nacl

Answer 25

Fluid obtained later after catheter placement can be | differentiated from CSF by urine reagent strip.

Question 26

LOR air issues

Answer 26

LOR using air might result in false LOR, as air is compressible. Use of air may cause venous air embolism, headache, pneumocephalus and patchy block.

Question 27

Test dose for epidural

Answer 27

The test dose for epidural anaesthesia includes 3 mL of 1.5% lidocaine with epinephrine 15 mcg.

Question 28

How can intravascular placement be detected exceptions?

Answer 28

An increase in heart rate by 20% is indicative of intravascular placement, except in patients on beta blockers, pregnant patients in active labour and patients under general anaesthetic.

Question 29

How can intravascular placement be detected in those on Beta bloqs

Answer 29

Systolic blood pressure changes of about 20 mmHg are used as an indicator of intravascular placement in patients on beta blockers.

Question 30

How can intravascular placement be detected in paeds

Answer 30

Peaked P waves and T-wave changes on ECG indicate intravascular placement in paediatrics.

Question 31

How an intrathecal placement be detected

Answer 31

Dense motor block within 5 minutes of test dose indicates intrathecal placement.

Question 32

When to give test dose to those in labour

Answer 32

In patients in active labour, the test dose must be given after a contraction.

Question 33

Elderly patients difference how does this affect spread

Answer 33

In elderly patients, there is a reduction in size of the intervertebral foramina, limiting the spread of local anaesthetics out of the epidural space.

Question 34

Should dose be changed in elderly why

Answer 34

Additionally, reduction in the fat content allows a more cephalad spread. Hence, the same dose as in adults will lead to a higher block. Consequently, dosing for the elderly should be reduced

Question 35

Pharmacokinetic considerations of epidural in children

Answer 35

1. Higher CNS toxicity: 2. higher free fraction and higher potential for toxicity 3. Higher initial plasma concentrations 4. Decreased duration of action 5. Drug accumulation after a continuous infusion. 6. Reduced drug metabolism and clearance: im

Question 36

Pharmacokinetic considerations of epidural in children Higher CNS toxicity:

Answer 36

blood–brain barrier is more permeable.

Question 37

Pharmacokinetic considerations of epidural in children higher free fraction and higher potential for toxicity

Answer 37

Lower α1-acid glycoprotein levels:.

Question 38

Pharmacokinetic considerations of epidural in children Decreased duration of action

Answer 38

due to high cardiac output increasing the uptake of local anaesthetic agents from neuraxial spaces.

Question 39

Pharmacokinetic considerations of epidural in children Reduced drug metabolism and clearance

Answer 39

immature liver and kidneys. | Due to this, decrease infusion rate after 24 hours.

Question 40

Regarding paediatric epidurals: What type of isomer is prefered why infusion?

Answer 40

Regarding paediatric epidurals: The single isomers like ropivacaine and levobupivacaine are preferred. The reduced toxicity and less motor blockade offer immense benefits particularly in infants and neonates. Prolonged infusion of ropivacaine (72 hours) has not shown increased toxicity. The vasoconstrictive properties of ropivacaine may delay its systemic absorption, reducing systemic toxicity.

Question 41

Regarding paediatric epidurals: Test doses symptoms of concern why late good way to monitor IV spread?

Answer 41

Test doses: ``` convulsions, arrhythmias and respiratory or cardiac arrest may be the first signs of toxicity in children, as procedures are mostly ``` performed under general anaesthetic. Monitoring ECG changes is a specific and more reliable method of detecting intravascular spread.

Question 42

Regarding paediatric epidurals: Additives @ what age why

Answer 42

Additives: ``` because of concerns regarding spinal cord toxicity and the risk of apnoea, additives are not commonly used below 6 months of age. ```

Question 43

Regarding paediatric epidurals: Anatomy and type of epidural

Answer 43

Anatomy: because the spinal cord extends till L3 and subarachnoid space till S3–S4 in infants, caudal epidural is preferred over lumbar epidurals. Also, due to less fat and fibrous tissue, it is easier to insert catheters to higher levels from lower approaches.

Question 44

When comparing lumbar epidural and thoracic epidural for abdominal surgery, the disadvantage of lumbar epidural is x 3

Answer 44

1 Hypotension and bradycardia is more common 2 Rescue analgesia is required more often 3 Motor block is extensive

Question 45

Hesitancy with thoracic epidural how may we compromise with level insertion

Answer 45

``` Difficulties in needle insertion, uncertain placement of catheters and the potential of neurological problems with thoracic epidural are the reasons for hesitancy in its use for abdominal surgery. ``` On the other hand, extension of lumbar block may be accepted as a compromise.

Question 46

Extension of lumbar block for abdominal surgery may not be ideal for 3 reasons,

Answer 46

But this may not be ideal for several reasons, as follows 1. Higher chances of bradycardia, vasodilatation and hypotension (Bezold–Jarisch reflex) with lumbar epidural. 2. Lumbar blocks are difficult to maintain (frequent regression seen) and need frequent rescue doses. ``` 3. Lumbar block cause more hypotension, and reflex vasoconstriction above the block may lead to myocardial ischaemia. ```

Question 47

Should we use lumbar epidurals for abdo surgery

Answer 47

Evidence suggests that lumbar epidurals should be avoided in patients undergoing abdominal or thoracic procedures

Question 48

Benefit of CSE x 3 (onset / dose / 1st stage)

Answer 48

Combined spinal epidural (CSE) offers benefits of both spinal and epidural. 1. The onset of surgical anaesthesia is comparable with a single-shot spinal and is faster than epidural anaesthesia. ``` 2. CSE allows the use of lower dose of anaesthetic for spinal and later prolongation of block if required with epidural administration of local anaesthetic. ``` 3. There is significant reduction in the duration of first-stage labour in primiparous patients.

Question 49

Disadvantages of CSE:

Answer 49

few disadvantages of CSE: 1. Inability to test the epidural catheter after spinal injection. 2. Possibility of failed epidural catheter. 3. The risk of greater spread of spinal drug after epidural injection

Question 50

What ways can CSE be performed

Answer 50

CSE can be done with two techniques: 1. needle-through-needle technique (NTN) 2. two separate injections at different levels

Question 51

What distance is important with CSE under / over How far does needle protrude in NTN

Answer 51

The knowledge of posterior epidural space distance (PED) is very important with NTN technique Underestimation of PED may result in spinal block failure and overestimation may cause damage to neural structures. The spinal needle protrudes 10–15 mm beyond the epidural needle in NTN technique

Question 52

Where is PED widest and narrowest

Answer 52

PED is widest in the lumbar region and | narrowest in the cervical region.

Question 53

What shape is the dural sac how does this affect paramedian NTN

Answer 53

The dural sac is triangular in shape, and thus paramedian approach increases the risk of failed spinal block with NTN technique.

Question 54

Describe NTN tech Benefit Disadvantage

Answer 54

NTN: This involves use of two separate needles for epidural and spinal, but use of same intervertebral space. This is associated with single skin puncture and hence less discomfort to the patient. However, as spinal block is given prior to epidural catheterisation, confirmation of epidural placement of catheter is not possible.

Question 55

Describe STN tech dsiadvantage

Answer 55

Separate spinal and epidural block (SNT) at two different intervertebral spaces. This is slightly more uncomfortable to the patient because of two skin punctures. It also takes more time than the NTN technique

Question 56

CSE Test dose what does it prove / not prove

Answer 56

The test dose (3 mL of 1.5% lignocaine and epinephrine 1:200 000) is used to rule out intravascular placement or intrathecal placement. If the catheter is intravascular, there would be tachycardia due to epinephrine, whereas a dense block with test dose will confirm intrathecal placement. The test dose does not confirm proper epidural placement.

Question 57

How might epidural cathter be confirmed

Answer 57

Nerve stimulation may be used as a technique for confirmation of epidural placement of catheter

Question 58

Confirmation of epidural space What strength confirms epidural what strength indicates outside what about subarachnoid how sensitive / specific is this test

Answer 58

Tsui test can be used for confirmation of epidural placement of catheter Epidural placement of catheter is confirmed if a motor response is obtained with a current strength of 1–10 mA motor response with > 10 mA indicates that the catheter is outside the epidural space, whereas a motor response with < 1 mA indicates subarachnoid location of catheter Its sensitivity and specificity is 100%.

Question 59

Failure of spinal block with CSE is mainly because needle length

Answer 59

1. spinal needle too short – not able to reach dura 2. spinal needle too long – deviation from the midline ``` 3. with NTN technique as spinal needle enters via the epidural needle, it is not stabilised by the surrounding ligaments. ``` Therefore, the hand must be very stable during injection of drug. Slight movement of hand may result in inappropriate drug delivery.

Question 60

Issues with NTN technique

Answer 60

``` 1. possibility of depositing metallic debris in the intrathecal space with NTN technique due to friction between the needles. ``` 2. There may be subarachnoid flux of epidurally administered local anaesthetic with CSE, leading to higher block than the same dose administered solely epidurally. ``` 3. Similarly intrathecally administered local anaesthetic may lead to higher block with CSE than single-shot spinal, as epidurally administered air or saline decreases the lumbar CSF volume. ```

Question 61

CSE in labour vs spinal Foetal brady PDPH Neuro injury Metal deposition

Answer 61

1. There is increased risk of foetal bradycardia with CSE as compared 2. The incidence of PDPH is rare 3. There is a higher risk of neurological injury with CSE when compared with a single-shot spinal. 4. There is no increased risk of metal deposition with NTN combined spinal epidural

Question 62

There is increased risk of foetal bradycardia with CSE as compared

Answer 62

with single-shot spinal. The rapid onset of analgesia with CSE causes a fall in catecholamine levels, leading to foetal bradycardia. However, this effect is transient, lasting only few minutes.

Question 63

The incidence of PDPH with CSE

Answer 63

with CSE because of the use of small gauge atraumatic spinal needles.

Question 64

Epidural volume extension’ (EVE)

Answer 64

``` Epidural volume extension’ (EVE) via a combined spinal–epidural (CSE) technique is the enhancement of a small-dose intrathecal block by epidural saline boluses. ```

Question 65

Epidural volume extension’ (EVE) | Advantages

Answer 65

The advantages are as follows. 1. Theoretically, it may help reduce the total intrathecal local anaesthetic dose required. However, a recent study did not find the technique dose-sparing. 2. It allows a faster motor recovery. 3 It does not alter the pain scores (VAS), peak sensory block height, time for sensory regression (to T10) and lowest systolic blood pressures.

Question 66

sacral vertebral foramina form a triangular canal

Answer 66

called the sacral canal, which is a continuation of the lumbar spinal canal.

Question 67

Sacral hiatus

Answer 67

Sacral hiatus is formed by failure of the laminae of S5 to meet, thus exposing its dorsal surface.

Question 68

Sacral cornuae are formed

Answer 68

are formed by inferior articular process of | S5 of each side.

Question 69

How to identify the sacral hiatus

Answer 69

``` Practically, the sacral hiatus is identified by drawing an equilateral triangle, the base of which is formed by the posterior superior iliac spine. ```

Question 70

Regarding the technique for caudal block short version

Answer 70

lateral decubitus 22-G intravenous canula short-bevel Strict asepsis angle of 45° plane of the sacrum horizontally and advanced by 2–3 mm

Question 71

technique for caudal block: | detailed

Answer 71

technique for caudal block: Best position for children is lateral decubitus with hips and knees flexed at 90°. Adults are best positioned prone for this block. A 22-G intravenous canula or a needle with a stellate is best used to avoid tissue coring into a hollow needle. The needle should be short-bevel to appreciate penetration of sacrococcygeal membrane. Strict asepsis is stressed because of frequent soiling from the anal area. The needle is first placed at an angle of 45° to the plane of the sacrum, and placed at the sacral hiatus to pierce the sacrococcygeal ligament. Then it is placed horizontally and advanced by 2–3 mm.

Question 72

Doses of local anaesthetic for caudal block (as described by Armitage) Sacro-lumbar

Answer 72

Sacro-lumbar 0. 25% bupivacaine 0. 5 mL/kg

Question 73

Doses of local anaesthetic for caudal block (as described by Armitage) Upper abdominal

Answer 73

Upper abdominal 0.25% bupivacaine 1 mL/kg

Question 74

Doses of local anaesthetic for caudal block (as described by Armitage) Mid-thoracic

Answer 74

Mid-thoracic 0. 25% bupivacaine 1. 25 mL/kg

Question 75

Caudal block vs Lumbar Vasodilation

Answer 75

``` Caudal block results in less peripheral vasodilatation than lumbar epidural, as sympathetic outflow from the spinal cord ends at L2. ```

Question 76

Caudal block autonomic effects

Answer 76

``` Caudal block results in blockage of S2–S4 contribution to parasympathetic system, affecting the bladder and the bowel distal to the colonic splenic flexure. ```

Question 77

Caudal block Dose v lumbar

Answer 77

The sacral canal varies widely anatomically, requiring almost double the dose of local anaesthetic as compared with lumbar epidural in order to achieve the same level of blockade

Question 78

methods of confirmation of caudal placement of the Tuohy needle Whoosh test:

Answer 78

``` Inject 2–3 mL of air in the caudal epidural space and auscultation over the thoracolumbar area produces the characteristic sound. It may cause patchy block and air embolism ```

Question 79

methods of confirmation of caudal placement of the Tuohy needle Swoosh test

Answer 79

Swoosh test: in paediatric patients, local anaesthetic or saline is used instead of air

Question 80

methods of confirmation of caudal placement of the Tuohy needle in epidural space nerve stimulator response

Answer 80

Correct needle placement in the epidural space can be identified with a nerve stimulator (current 1–10 mA) and anal sphincter contraction as the end response

Question 81

methods of confirmation of caudal placement of the Tuohy needle in epidural space Is ultrasound useful

Answer 81

Ultrasound may be useful in children < 6 months old, as after this age there is ossification of vertebral bodies preventing good visualisation

Question 82

Uses of caudal epidural block: x 3

Answer 82

Uses of caudal epidural block: 1 Caudal block is used for surgical procedures both above and below the diaphragm in paediatrics. 2 It may be used for labour analgesia, gynaecological, lower-limb and anal surgeries. 3 It is mainly used for chronic pain management in adults

Question 83

Caudal contrast + Block

Answer 83

‘Christmas tree’ appearance is normally seen on injection of contrast in the caudal space. It is due to spread of the dye in the caudal canal and along the nerve roots as they exit the vertebral column. Epidural adhesions are diagnosed with its characteristic absence.

Question 84

In order place risk of last epidural vs brachial plexus v caudal

Answer 84

The risk of local anaesthetic toxicity is as follows: caudal > brachial plexus block > lumbar or thoracic epidural

Question 85

ECG change after IV Local anaesthetic what other changes

Answer 85

T-wave changes on the ECG are the earliest changes in paediatric patients following ``` intravascular placement of local anaesthetic following caudal block. These are then followed by heart rate and blood pressure changes ```