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EDRA > 4.2 Central Neuraxial Blocks - Epidural > Flashcards

4.2 Central Neuraxial Blocks - Epidural Flashcards

1
Q

Epidural space

Where

Extends

A

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.

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2
Q

Epidural space

contains

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

There is no free fluid present.

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3
Q

Batson’s venous plexus

A 
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).

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4
Q

Anterior dura v posterior nerve supply

periosteoum

flavum

A

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.

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5
Q

Posterior border of epidural space

A

The ligamentum flavum
forms the posterior
boundary of epidural space.

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6
Q

Epidural in elderly /obese

A

epidural fat increases
with obesity and decreases with age.

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

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7
Q

Spinous processes angulation

Cervical
Thoracic
Lumbar

A 
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

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8
Q

Greatest degree of angulation Spinous processes

A

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.

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9
Q

Vertebral levels and landmarks

Most prominent

spine scapula

inferior angle scapula

line connecting iliac crest

line connecting post inf iliac spine

A

C7: vertebrae prominens

T3: spine of scapula

T7: inferior angle of scapula

L4: line connecting iliac crest

S2: line connecting posterior inferior iliac spine.

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10
Q

Absolute contraindications epidural

A

Absolute contraindications for epidural blockade include

patient refusal, 
infection at injection site, 
allergy to local anaesthetic, 
raised intracranial pressure 
and hypovolemia.
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11
Q

Relative contraindications epidural

A 
Relative contraindications include
a 
platelet count < 100 000 per mL, 
hypertension, 
sepsis, 
anatomical abnormality of spine, 
previous spinal surgery 
and an uncooperative patient
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12
Q

physiological effects of epidural anaesthesia

Cardiovascular Block below + Above T4:

A

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

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13
Q

physiological effects of epidural anaesthesia

Respiratory

A

Respiratory
Minimal effects on pulmonary function

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

Forced expiratory volumes reduced

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14
Q

physiological effects of epidural anaesthesia

Renal

A

Renal

Urinary retention may occur from
blockade of S2–S4 fibres

Due to renal autoregulation,
renal blood flow is maintained.

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15
Q

physiological effects of epidural anaesthesia

Gastrointestinal

A

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

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16
Q

physiological effects of epidural anaesthesia

Neuroendocrine

A

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

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17
Q

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

A

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.

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18
Q

Additives to epidurals

Epinephrine

Duration

how

added benefit?

A 
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.

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19
Q

Additives to epidurals

Epi affect on BP

A

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

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20
Q

Additives to epidurals

Soda Bic

Benefit

How

A 
Adding bicarbonate to 
local anaesthetic 
increases the unionised form,
hence more drug can 
penetrate the lipid membrane, thereby
increasing the speed of onset.
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21
Q

Additives to epidurals

Soda Bic

Solution for ligno / ropiv

A

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.

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22
Q

Site of epidural injection

What affects density

What affects height

A

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.

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23
Q

Epidural height affected by patient weight and height?

A

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

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24
Q

LOR to fluid described by

What sign given

issues if use too much NaCL

A

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.

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25
Q

How differentiate fluid from catheter csf v nacl

A

Fluid obtained later after catheter placement can be

differentiated from CSF by urine reagent strip.

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26
Q

LOR air issues

A

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.

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27
Q

Test dose for epidural

A

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

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28
Q

How can intravascular placement be detected

exceptions?

A

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.

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29
Q

How can intravascular placement be detected in those on Beta bloqs

A

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

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30
Q

How can intravascular placement be detected in paeds

A

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

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31
Q

How an intrathecal placement be detected

A

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

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32
Q

When to give test dose to those in labour

A

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

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33
Q

Elderly patients difference

how does this affect spread

A

In elderly patients, there is a
reduction in size of the intervertebral foramina,

limiting the spread of
local anaesthetics out
of the epidural space.

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34
Q

Should dose be changed in elderly

why

A

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

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35
Q

Pharmacokinetic considerations of epidural in children

A
  1. Higher CNS toxicity:

2.
higher free fraction and higher
potential for toxicity

3.
Higher initial plasma concentrations

  1. Decreased duration of action

5.
Drug accumulation after a continuous infusion.

  1. Reduced drug metabolism and clearance: im
36
Q

Pharmacokinetic considerations of epidural in children

Higher CNS toxicity:

A

blood–brain barrier is more permeable.

37
Q

Pharmacokinetic considerations of epidural in children

higher free fraction and higher
potential for toxicity

A

Lower α1-acid glycoprotein levels:.

38
Q

Pharmacokinetic considerations of epidural in children

Decreased duration of action

A

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

39
Q

Pharmacokinetic considerations of epidural in children

Reduced drug metabolism and clearance

A

immature liver and kidneys.

Due to this, decrease infusion rate after 24 hours.

40
Q

Regarding paediatric epidurals:

What type of isomer is prefered

why

infusion?

A

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.

41
Q

Regarding paediatric epidurals:

Test doses

symptoms of concern
why late

good way to monitor IV spread?

A

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.

42
Q

Regarding paediatric epidurals:

Additives
@ what age

why

A

Additives:

because of concerns regarding 
spinal cord toxicity and the
risk of apnoea, 
additives are not commonly used 
below 6 months of
age.
43
Q

Regarding paediatric epidurals:

Anatomy and type of epidural

A

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.

44
Q

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

x 3

A

1 Hypotension and bradycardia is more common

2 Rescue analgesia is required more often

3 Motor block is extensive

45
Q

Hesitancy with thoracic epidural

how may we compromise with level insertion

A 
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.

46
Q

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

A

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.
47
Q

Should we use lumbar epidurals for abdo surgery

A

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

48
Q

Benefit of CSE

x 3

(onset / dose / 1st stage)

A

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.

49
Q

Disadvantages of CSE:

A

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

50
Q

What ways can CSE be performed

A

CSE can be done with two techniques:

  1. needle-through-needle technique (NTN)

2.
two separate injections at different levels

51
Q

What distance is important with CSE

under / over

How far does needle protrude in NTN

A

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

52
Q

Where is PED widest and narrowest

A

PED is widest in the lumbar region and

narrowest in the cervical region.

53
Q

What shape is the dural sac

how does this affect paramedian NTN

A

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

54
Q

Describe NTN tech

Benefit

Disadvantage

A

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.

55
Q

Describe STN tech

dsiadvantage

A

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

56
Q

CSE Test dose

what does it prove / not prove

A

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.

57
Q

How might epidural cathter be confirmed

A

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

58
Q

Confirmation of epidural space

What strength confirms epidural

what strength indicates outside

what about subarachnoid

how sensitive / specific is this test

A

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%.

59
Q

Failure of spinal block with CSE is mainly because

needle length

A

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.

60
Q

Issues with NTN technique

A 
1. possibility of 
depositing metallic debris 
in the intrathecal space
with NTN technique due to 
friction between the needles.
  1. 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.
61
Q

CSE in labour vs spinal

Foetal brady

PDPH

Neuro injury

Metal deposition

A
  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
62
Q

There is increased risk of foetal bradycardia with CSE as compared

A

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.

63
Q

The incidence of PDPH with CSE

A

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

64
Q

Epidural volume extension’ (EVE)

A 
Epidural volume extension’ (EVE) via a 
combined spinal–epidural
(CSE) technique is the 
enhancement of a small-dose 
intrathecal block by
epidural saline boluses.
65
Q

Epidural volume extension’ (EVE)

Advantages

A

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.

66
Q

sacral vertebral foramina form a triangular canal

A

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

67
Q

Sacral hiatus

A

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

68
Q

Sacral cornuae are formed

A

are formed by inferior articular process of

S5 of each side.

69
Q

How to identify the sacral hiatus

A 
Practically, the sacral hiatus is 
identified by drawing 
an equilateral triangle, 
the base of which is formed by the 
posterior superior iliac spine.
70
Q

Regarding the technique for caudal block

short version

A

lateral decubitus

22-G intravenous canula

short-bevel

Strict asepsis

angle of 45° plane of the sacrum
horizontally and advanced by 2–3 mm

71
Q

technique for caudal block:

detailed

A

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.

72
Q

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

Sacro-lumbar

A

Sacro-lumbar

  1. 25% bupivacaine
  2. 5 mL/kg
73
Q

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

Upper abdominal

A

Upper abdominal
0.25% bupivacaine
1 mL/kg

74
Q

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

Mid-thoracic

A

Mid-thoracic

  1. 25% bupivacaine
  2. 25 mL/kg
75
Q

Caudal block vs Lumbar

Vasodilation

A 
Caudal block results in 
less peripheral vasodilatation 
than lumbar epidural, 
as sympathetic outflow from the 
spinal cord ends at L2.
76
Q

Caudal block

autonomic effects

A 
Caudal block results in blockage of 
S2–S4 contribution to
parasympathetic system, 
affecting the bladder and the bowel distal
to the colonic splenic flexure.
77
Q

Caudal block Dose v lumbar

A

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

78
Q

methods of confirmation of caudal placement of the Tuohy needle

Whoosh test:

A 
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
79
Q

methods of confirmation of caudal placement of the Tuohy needle

Swoosh test

A

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

80
Q

methods of confirmation of caudal placement of the Tuohy needle in epidural space

nerve stimulator
response

A

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

81
Q

methods of confirmation of caudal placement of the Tuohy needle in epidural space

Is ultrasound useful

A

Ultrasound may be useful in children

< 6 months old, as after this age

there is ossification of vertebral
bodies preventing good visualisation

82
Q

Uses of caudal epidural block:

x 3

A

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

83
Q

Caudal contrast + Block

A

‘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.

84
Q

In order place risk of last

epidural vs brachial plexus v caudal

A

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

85
Q

ECG change after IV Local anaesthetic

what other changes

A

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

EDRA (26 decks)

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