4.1 Central Neuraxial Blocks - Spinal Flashcards
Absolute contraindications for spinal anaesthesia
Absolute contraindications for spinal anaesthesia
include
- patient refusal,
- raised intracranial hypertension,
- neurological disease of indeterminate origin,
- coagulopathy,
- severe hypovolaemia
- local infection.
Relative contraindications
Relative contraindications include
- systemic sepsis,
- surgery of indeterminate duration,
- arthritis,
- kyphoscoliosis
- previous lumbar surgery.
Spinal and MS patients
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
Spinal cord has three coverings
Dura mater
Arachnoid mater
Pia mater
Dura mater
border
(outermost) extends from foramen magnum to S2.
Arachnoid mater
Arachnoid mater (middle) extends to S2.
Pia mate
Pia mater (innermost) ends in the filum terminale
Supraspinous ligament
Supraspinous ligaments extend from
C7 to sacrum
connecting the tips of
the spinous processes.
Above C7, they are called the ligamentum nuchae.
How are the spinous processes connected
How are laminae connected
How are vertebral bodies held together
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.
Structures pierced while performing
a spinal anaesthetic via midline
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.
Structures pierced while performing
a spinal anaesthetic via paramedian approach
what is not pierced vs midline
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.
Spinal nerves
How many
Do each have 2 components?
what are those componenets
1
Thirty-one pairs of spinal nerves
arise from the spinal cord with
anterior motor and posterior sensory roots.
How are the spinal nerves named
From vertebral body above or below
Does this differ anywhere
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).
What happens dorsal nerve roots
The dorsal nerve roots
divide into two or three
bundles during their exit
and
redivide further before forming
dorsal root ganglia.
What happens ventral roots
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.
What factors affect spread in SA space
The factors affecting the spread of
local anaesthetic in subarachnoid
space include the following.
- Drug factors
- 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).
Drug factors
Drug factors: baricity, volume, specific gravity and dose of local anaesthetic.
Patient factors
Patient factors:
raised intra-abdominal pressure
(pregnancy, obesity, ascites),
spinal column anatomy,
patient position and
patient height.
Technique
Technique:
direction of the needle bevel and site of injection.
Effect of Epinephrine and phenyl
Epinephrine and phenylephrine
are both vasoconstrictors.
They prolong the duration of action
of local anaesthetic
by decreasing their systemic absorption.
Risk of Epinephrine
Because of its vasoconstrictive properties,
epinephrine may cause anterior spinal artery ischaemia.
Risk of phenyl
The risk of transient neurological symptoms (TNSs) has been shown to
increase with the use of phenylephrine.
Clonidine effect on SAB
Clonidine prolongs both sensory and motor blockade.
Effect of AChI on SAB
(how exert effect)
problems
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.
The risk factors for hypotension following spinal anaesthetic include
9
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.
Hypotension during spinal
What agents are best
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.
Do Fluids help hypotension
Coloading of fluids at the time
of induction has been shown to be
superior to the prior infusion of fluids.
How may position help / affect hyptotension
What may be helpful
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.
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
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.
Risk factors for bradycardia with spinal anaesthetic
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)
High spinal
Where does it affect
A high spinal block
does not affect the
cervical segments usually.
Affect of High spinal on respiration (expiration)
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).
Affect of High spinal on respiration (inspiration)
abg affect
does dyspnoea require intubation
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).
Pencil-point needles
Sprotte and Whitacre
require more force to insert than bevel-tip
needles, they provide better tactile sensation of the layers of the ligaments
encountered
Needles with cutting bevels
Pitkin (short cutting bevel)
Quincke (medium cutting bevel)
Needle with non-cutting bevel
Greene needle
How can be pdph reduced with regards to needle
incidence of post-dural
puncture headache (PDPH) can
be reduced by directing the
bevel of the needle longitudinally.
what is the benefit of an introducer
where is it placed
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.
The Taylor approach
where
what position
needle insertion direction
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.
Intrathecal additives
Opiods (and LA - how work)
Opioids act
synergistically along with
local anaesthetics in
intrathecal space by
binding to μ-opioid receptors.
Issue with morphine vs fentanyl
Morphine may cause
delayed respiratory depression (24 hours),
whereas lipophilic opioids
like fentanyl and sufentanil cause
immediate respiratory depression (20–30 minutes).
How does fentanyl affect block
Small doses of fentanyl intensify the blockade without prolonging it
Clonidine affect on block
only when given intrathecal?
Clonidine intensifies and prolongs
both sensory and motor blockade.
This effect is seen with intrathecal,
oral (premedication) or
intravenous route of clonidine.
Neostigmine affect on block
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
sequence of blockade of nerve fibres is as follows
sequence of blockade of nerve fibres is as follows:
B fibres (preganglionic sympathetic) > C fibres (cold sensation) > Aδ (pinprick) > Aβ (touch) > Aα (motor)
How is nerve blockade recovered
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.
zone of differential blockade in spinal anaesthesia
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.
What is the CSF density
Does it change
The density of CSF varies from
1.00033 g/mL to 1.00067 g/mL.
It decreases with increase in temperature.
What is Baricity
Baricity is ratio of density of local anaesthetic to CSF.
Hyperbaric
vs CSF
How
Duratin
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.
Isobaric solution
hypobaric are
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
Specific gravity
Of LA
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.
Useful tips with Baricity
position
type block with hyper
supine how is spread
how hypobaric
duration of hyper v iso
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.
PDPH Incidence
Expert using non cutting
Incidence is
< 1% if procedure is performed
by an expert using noncutting
needles (Whitacre or Sprotte).
PDPH incidence in OBS
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.
Dural tear with a tuohy
PDPH incidence
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.
PDPH higher with quincke or whitacre
Higher with cutting needles
(Quincke) than with non-cutting
needles (Whitacre or Sprotte).
mechanism in the development of PDPH includes
3 mech
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
Typical features of PDPH are as follows.
Hx
Onset
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.
Typical features of PDPH are as follows.
Position
distribution
a/w
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.
PDPH RF
Patient-related
4
Young adults (vs elderly)
Female sex (vs males)
Obstetric patients
(vs nonobstetric patients)
History of previous headaches
Procedure-related RF PDPH
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)
PDPH w/ Paramedian
Cathter with puncture?
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.
Management of post-dural puncture headache
Cons + pharma
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
Management of post-dural puncture headache
Interventional
Interventional
intrathecal opioids
epidural saline
epidural blood patch (considered ‘gold standard’): success rate is 70%–90%
