4.1 Central Neuraxial Blocks - Spinal

Question 1

Absolute contraindications for spinal anaesthesia

Answer 1

Absolute contraindications for spinal anaesthesia
include

1. patient refusal,
2. raised intracranial hypertension,
3. neurological disease of indeterminate origin,
4. coagulopathy,
5. severe hypovolaemia
6. local infection.

Question 2

Relative contraindications

Answer 2

Relative contraindications include

1. systemic sepsis,
2. surgery of indeterminate duration,
3. arthritis,
4. kyphoscoliosis
5. previous lumbar surgery.

Question 3

Spinal and MS patients

Answer 3

Central neuraxial block in patients with multiple sclerosis is
controversial. There is no clinical study which has shown that spinal
anesthesia worsens pre-existing neurological disease. Perioperative
surgical stress may exacerbate the condition, and hence a central
neuraxial block may be preferred

Question 4

Spinal cord has three coverings

Answer 4

Dura mater
Arachnoid mater
Pia mater

Question 5

Dura mater

border

Answer 5

(outermost) extends from foramen magnum to S2.

Question 6

Arachnoid mater

Answer 6

Arachnoid mater (middle) extends to S2.

Question 7

Pia mate

Answer 7

Pia mater (innermost) ends in the filum terminale

Question 8

Supraspinous ligament

Answer 8

Supraspinous ligaments extend from
C7 to sacrum
connecting the tips of
the spinous processes.

Above C7, they are called the ligamentum nuchae.

Question 9

How are the spinous processes connected

How are laminae connected

How are vertebral bodies held together

Answer 9

The spinous processes are
interconnected by the interspinous ligaments.

The laminae are connected by the ligamentum flavum.

The vertebral bodies are held together by the anterior and the posterior longitudinal ligaments.

Question 10

Structures pierced while performing

a spinal anaesthetic via midline

Answer 10

Structures pierced while performing a spinal anaesthetic via midline approach are

1 skin

2 subcutaneous tissues

3 supraspinous ligaments,

4 interspinous ligaments

5 ligamentum flavum

6 dura mater

7 subdural space

8 arachnoid mater

and

9 subarachnoid space.

Question 11

Structures pierced while performing
a spinal anaesthetic via paramedian approach

what is not pierced vs midline

Answer 11

However, via the paramedian approach
all the above structures are
encountered
except the

supraspinous
and
interspinous ligaments.

1 skin

2 subcutaneous tissues

3 ligamentum flavum

4 dura mater

5 subdural space

6 arachnoid mater

and

7 subarachnoid space.

Question 12

Spinal nerves

How many

Do each have 2 components?
what are those componenets

Answer 12

1
Thirty-one pairs of spinal nerves
arise from the spinal cord with
anterior motor and posterior sensory roots.

Question 13

How are the spinal nerves named

From vertebral body above or below

Does this differ anywhere

Answer 13

The spinal nerves are named
as per the intervertebral foramen
from which they exit.

In the cervical region,
they are named according to the
lower cervical vertebral body

(C3 emerges from intervertebral foramen
formed by C2 and C3),

but in the
thoracic and lumbar region
they are named

according to the
upper vertebral body

(L3 emerges from intervertebral
foramen formed by L3 and L4).

Question 14

What happens dorsal nerve roots

Answer 14

The dorsal nerve roots
divide into two or three
bundles during their exit

and

redivide further before forming
dorsal root ganglia.

Question 15

What happens ventral roots

Answer 15

Most ventral nerve roots exit
as a single bundle,

explaining the slower onset of
motor blockade because
of smaller surface area for
local anaesthetic action.

Question 16

What factors affect spread in SA space

Answer 16

The factors affecting the spread of
local anaesthetic in subarachnoid
space include the following.

1. Drug factors
2. Patient factors

3 Technique

Concentration has no effect 
on the spread of local anaesthetic, 
as a new concentration is 
formed after mixing 
with the cerebrospinal fluid (CSF).

Question 17

Drug factors

Answer 17

Drug factors: 
baricity, 
volume, 
specific gravity 
and dose of local
anaesthetic.

Question 18

Patient factors

Answer 18

Patient factors:
raised intra-abdominal pressure
(pregnancy, obesity, ascites),

spinal column anatomy,
patient position and
patient height.

Question 19

Technique

Answer 19

Technique:

direction of the needle bevel and site of injection.

Question 20

Effect of Epinephrine and phenyl

Answer 20

Epinephrine and phenylephrine
are both vasoconstrictors.

They prolong the duration of action
of local anaesthetic
by decreasing their systemic absorption.

Question 21

Risk of Epinephrine

Answer 21

Because of its vasoconstrictive properties,

epinephrine may cause anterior spinal artery ischaemia.

Question 22

Risk of phenyl

Answer 22

The risk of transient neurological symptoms (TNSs) has been shown to
increase with the use of phenylephrine.

Question 23

Clonidine effect on SAB

Answer 23

Clonidine prolongs both sensory and motor blockade.

Question 24

Effect of AChI on SAB

(how exert effect)

problems

Answer 24

Acetylcholinesterase inhibitors
like neostigmine

exert their effect by increasing
acetylcholine and nitric oxide.

However, their use is limited
by side effects such as 
nausea, 
vomiting, 
agitation, 
bradycardia,
restlessness and 
lower-limb weakness.

Question 25

The risk factors for hypotension following spinal anaesthetic include

9

Answer 25

The risk factors for hypotension following spinal anaesthetic include

1 obesity (high body mass index)

2 pre-existing hypertension

3 hypovolaemia

4 age > 40 years

5 combined general and spinal anaesthetic

6 chronic alcohol consumption

7 emergency surgery

8 high sensory blockade

9 addition of vasoconstrictor to local anaesthetic solution.

Question 26

Hypotension during spinal

What agents are best

Answer 26

Combined alpha and beta agonists
are superior to
pure alpha agonist in treating hypotension,

and
ephedrine is currently the drug of choice.

Phenylephrine can be used, especially if tachycardia is present.

Question 27

Do Fluids help hypotension

Answer 27

Coloading of fluids at the time
of induction has been shown to be
superior to the prior infusion of fluids.

Question 28

How may position help / affect hyptotension

What may be helpful

Answer 28

Reverse Trendelenburg position
may stop the cephalad anaesthetic spread,

but may lead to marked hypotension
because of venous pooling in lower limbs.

Flexion of the operation table
may be helpful by elevating the
legs but preventing cephalad spread
of local anaesthetic.

Question 29

Appropriate sensory levels of blockade for common surgeries are as follows:

Caesarean section/upper abdominal surgery

gynaecological and urological surgeries

vaginal delivery of foetus

transurethral resection of prostate

lower extremity surgery with tourniquet

perineal surgery

Answer 29

Appropriate sensory levels of blockade for common surgeries are as
follows:

Caesarean section/upper abdominal surgery – T4

gynaecological and urological surgeries – T6

vaginal delivery of foetus – T10

transurethral resection of prostate – T10

lower extremity surgery with tourniquet – T10

perineal surgery – S2–S5.

Question 30

Risk factors for bradycardia with spinal anaesthetic

Answer 30

1 ASA class 1

2 prolonged PR interval (heart blocks)

3 preoperative beta-blocker therapy

4 male gender

5 baseline heart rate < 60 bpm

6 sensory block above T5

7 younger age groups (age < 40 years)

Question 31

High spinal

Where does it affect

Answer 31

A high spinal block
does not affect the
cervical segments usually.

Question 32

Affect of High spinal on respiration (expiration)

Answer 32

High spinal block paralyses
the abdominal and intercostal muscles
affecting forced expiration.

Therefore, there is a
decrease in expiratory reserve volume,
peak expiratory flow and maximum minute
ventilation (all forced expiratory volumes).

Question 33

Affect of High spinal on respiration (inspiration)

abg affect

does dyspnoea require intubation

Answer 33

There is relative sparing of
phrenic nerve and cervical area.

Hence, inspiration is minimally affected.

Arterial blood gas measurements do not change in a spontaneously breathing patient.

Inability to feel the chest wall may result in dyspnoea.

This is addressed by reassurance (not intubation).

Question 34

Pencil-point needles

Answer 34

Sprotte and Whitacre

require more force to insert than bevel-tip
needles, they provide better tactile sensation of the layers of the ligaments
encountered

Question 35

Needles with cutting bevels

Answer 35

Pitkin (short cutting bevel)

Quincke (medium cutting bevel)

Question 36

Needle with non-cutting bevel

Answer 36

Greene needle

Question 37

How can be pdph reduced with regards to needle

Answer 37

incidence of post-dural
puncture headache (PDPH) can
be reduced by directing the
bevel of the needle longitudinally.

Question 38

what is the benefit of an introducer

where is it placed

Answer 38

Spinal needles with introducers
help by preventing
contamination of CSF with epidermis,

which may lead to formation of
dermal spinal tumors.

The introducer is
placed in the interspinous ligament.

Question 39

The Taylor approach

where

what position

needle insertion direction

Answer 39

The Taylor approach is a
paramedian approach at L5–S1 interface,

which is the largest interspace.

It can be done in the
sitting, prone or lateral positions.

The needle is inserted
1 cm inferior and 1 cm medial to
the posterior superior iliac spine

and directed at an angle of
45°–55° cephalad.

Question 40

Intrathecal additives

Opiods (and LA - how work)

Answer 40

Opioids act

synergistically along with
local anaesthetics in

intrathecal space by
binding to μ-opioid receptors.

Question 41

Issue with morphine vs fentanyl

Answer 41

Morphine may cause
delayed respiratory depression (24 hours),

whereas lipophilic opioids
like fentanyl and sufentanil cause
immediate respiratory depression (20–30 minutes).

Question 42

How does fentanyl affect block

Answer 42

Small doses of fentanyl intensify the blockade without prolonging it

Question 43

Clonidine affect on block

only when given intrathecal?

Answer 43

Clonidine intensifies and prolongs
both sensory and motor blockade.

This effect is seen with intrathecal,
oral (premedication) or
intravenous route of clonidine.

Question 44

Neostigmine affect on block

Answer 44

Neostigmine,
an acetylcholinesterase inhibitor, increases the
availability of endogenous acetylcholine.

Activation of acetylcholine
receptors is thought to contribute
to an endogenous form of analgesia.

However, it is not used because the
incidence of nausea and vomiting
is high

Question 45

sequence of blockade of nerve fibres is as follows

Answer 45

sequence of blockade of nerve fibres is as follows:

B fibres (preganglionic sympathetic) > 
C fibres (cold sensation) > 
Aδ (pinprick) > 
Aβ (touch) > 
Aα (motor)

Question 46

How is nerve blockade recovered

Answer 46

The recovery is in the reverse order.

This explains one of the reasons for the
zone of differential blockade in spinal anaesthesia:

sympathetic block is two segments higher than sensory block, which is two segments higher than
motor blockade. These zones of differential blockade remain constant during
emergence from spinal anaesthetic.

Question 47

zone of differential blockade in spinal anaesthesia

Answer 47

zone of differential blockade in spinal anaesthesia:

sympathetic block is two segments higher
than sensory block,

which is two segments higher than
motor blockade.

These zones of differential blockade
remain constant during
emergence from spinal anaesthetic.

Question 48

What is the CSF density

Does it change

Answer 48

The density of CSF varies from
1.00033 g/mL to 1.00067 g/mL.

It decreases with increase in temperature.

Question 49

What is Baricity

Answer 49

Baricity is ratio of density of local anaesthetic to CSF.

Question 50

Hyperbaric

vs CSF
How

Duratin

Answer 50

Hyperbaric solutions have greater density to CSF.

Local anaesthetics are made
hyperbaric by adding glucose 50–80 mg/mL.

Hyperbaric solutions have a
shorter duration of action than plain
solutions.

Question 51

Isobaric solution

hypobaric are

Answer 51

Isobaric solutions have the same density as CSF

whereas hypobaric are less dense than CSF.

Local anaesthetics are made hypobaric by adding distilled water.
Hypobaric anaesthetic solution may be used for rectal and perineal
surgery in lateral decubitus or prone jackknife position

Question 52

Specific gravity

Of LA

Answer 52

Specific gravity is the ratio of density of a substance to the density of water.

Local anaesthetics behave as
isobaric solution if the density of the solution
is within the mean of plus or minus the standard deviation of density of CSF.

Question 53

Useful tips with Baricity

position

type block with hyper

supine how is spread

how hypobaric

duration of hyper v iso

Answer 53

1
Hyperbaric and hypobaric solutions
can be made to spread by
altering patient position.

2
Hyperbaric solutions allow for
providing a saddle block.

3 
In a supine patient, 
spread of a hyperbaric 
solution is the maximum,
followed by isobaric solutions, 
while it is the least with hypobaric solutions.

4
Hypobaric solutions are not available
commercially and must be
prepared at bedside.

5
Hyperbaric solutions have a
shorter duration of action than plain
solutions.

Question 54

PDPH Incidence

Expert using non cutting

Answer 54

Incidence is
< 1% if procedure is performed
by an expert using noncutting
needles (Whitacre or Sprotte).

Question 55

PDPH incidence in OBS

Answer 55

Incidence is higher in the obstetric population (1.7%), since the
procedure is technically difficult (exaggerated lordosis) and pregnant
patients may not be able to sit very still for the procedure.

Question 56

Dural tear with a tuohy

PDPH incidence

Answer 56

Should a dural tear happen using a
Tuohy needle (16 G is usually used for adults),
then 50%–80% of those patients
go on to develop PDPH.

Question 57

PDPH higher with quincke or whitacre

Answer 57

Higher with cutting needles
(Quincke) than with non-cutting
needles (Whitacre or Sprotte).

Question 58

mechanism in the development of PDPH includes

3 mech

Answer 58

Loss of cerebrospinal fluid
Cerebral vasodilatation
Raised intracranial pressure

The loss of CSF from the intrathecal space:
this leads to intracranial
hypotension to start with,
causing the sagging of cranial structures in
upright position, resulting in headache.

Compensatory cerebral venodilatation
(in keeping with the Monro– Kelly doctrine,
which states that the sum of volumes of the brain, CSF
and intracranial blood is constant).

Raised intracranial pressure: secondary to cerebral venodilatation

Question 59

Typical features of PDPH are as follows.

Hx

Onset

Answer 59

Typical features of PDPH are as follows.

1
History of a dural puncture 
(following spinal) or a 
possible dural tap
(following epidural).

2
Onset is usually delayed (12–48 hours)
but can be seen up to 5 days
after a procedure.

Question 60

Typical features of PDPH are as follows.

Position

distribution

a/w

Answer 60

3
Headache is typically positional in character
(most severe in upright
position, while decreases with patient recumbent).

an increase in severity of the headache on standing is the sine qua non
of PDPH.

4
Is almost always bilateral in distribution.

5 
Associated symptoms of 
nausea, 
vomiting, 
neck stiffness,
visual/auditory disturbances 
or cranial nerve involvement.

Question 61

PDPH RF

Patient-related
4

Answer 61

Young adults (vs elderly)

Female sex (vs males)

Obstetric patients
(vs nonobstetric patients)

History of previous headaches

Question 62

Procedure-related RF PDPH

Answer 62

Larger-gauge needles (vs finer needles)

Cutting needles (vs non-cutting)

Higher number of dural punctures

Insertion of needle bevel perpendicular
to the direction of fibres of
ligamentum flavum (cutting rather than splitting)

Non-expert operator

Dural puncture following epidural than a spinal
(bigger defect)

Question 63

PDPH w/ Paramedian

Cathter with puncture?

Answer 63

paramedian approaches may allow better sealing of defects, lowering
the incidence of PDPH. Recent evidence suggests that threading a catheter
into the subarachnoid space may reduce the incidence of PDPH.

Question 64

Management of post-dural puncture headache

Cons + pharma

Answer 64

Conservative
bed rest, hydration, abdominal binders

Pharmacological
paracetamol,
non-steroidal anti-inflammatory drugs, codeine

strong opioids (as temporary measure)

cerebral vasoconstrictors:
caffeine, methylxanthine, theophylline

5-HT1 agonist: sumatriptan

adrenocorticotropic hormone

Question 65

Management of post-dural puncture headache

Interventional

Answer 65

Interventional
intrathecal opioids
epidural saline
epidural blood patch (considered ‘gold standard’): success rate is 70%–90%