6.4 Systemic disease Flashcards
Lumbar epidural anaesthesia affect muscles
Lumbar epidural anaesthesia
paralyses the abdominal and intercostal muscles
Respiratory parameter are affected in lumbar
Therefore the
effort-dependent respiratory parameters are affected:
FEV1 (forced expiratory volume in the first second),
FVC (forced vital capacity)
PEFR (peak expiratory flow rate)
Respiratory parameter unaffected in lumbar epi
Other respiratory parameters are unchanged: tidal volume, minute ventilation, respiratory rate, closing capacity FRC (functional residual capacity).
Brachial plexus blocks affect on respiratory
supraclavicular, infraclavicular, interscalene
may paralyze the diaphragm
thereby reduce FEV1 and FVC.
Axillary affect on respiration
Axillary block has no effect on diaphragm and therefore on any
respiratory parameter
Pulmonary function preservation post thoracotomy is better with what block
Various studies have shown that
after thoracotomy,
preservation of pulmonary function
is better with paravertebral blockade than
epidural or intercostal blockade
chronic renal disease
Affect of spinal and thoracic anaesthesia on RBF
what level is it affected
renal blood flow
is not affected
by spinal and
lower-thoracic anaesthesia.
However,
higher thoracic blocks up to
T1 have decreased renal
blood flow in various studies
Graft function in renal transplant patients affect by GA or Neuraxial
Graft function in renal transplant patients is not affected by either general anaesthesia or central neuraxial anaesthesia
uremic patients affect on circulation
how does this affect absorption following PNB
hyperdynamic circulation,
resulting in increased
absorption of local anaesthetic
following peripheral
nerve blockade.
In uremic patients,
pH changes affect on LA
Acidosis increases the
free fraction of local anaesthetic
like bupivacaine by
decreasing protein binding
What counters the pH changes in Uremic patients
However, uremic patients have
increase in levels of α1-acid glycoprotein,
resulting in increase in
protein binding and
decreasing volume of distribution
Thus these two opposing effects try to balance
each other, but the effect of acidosis predominates
Does any method of anaesthesia help with AV fistula
GA v RA
Creation of arteriovenous fistula
is one of the
commonest surgeries in
patients with chronic renal failure.
Various studies have shown that there is
increased blood flow through
fistula following brachial plexus block or
general anaesthesia.
Does any method of anaesthesia help with AV fistula
Local infiltration
Local anaesthetic infiltration
has not shown similar
increase in blood flow
through the fistula.
Does any of method of anaesthesia improve outcome
The final outcome has remained
almost the same,
independent of the type of anaesthesia
Hepatic extraction ratios
high
Local anaesthetics depending on
hepatic blood flow for their clearance
are said to have high hepatic extraction ratio
(e.g. etidocaine).
Hepatic extraction ratios
Low
Local anaesthetics depending on hepatic enzymatic activity for their clearance are said to have low hepatic extraction ratio (e.g. bupivacaine).
Hepatic extraction ratios
Lignocaine is dependent on
both hepatic blood flow and enzymatic
activity and has intermediate
hepatic extraction ratio.
regional anaesthesia in patients
with hepatic disease
severe - how are mechanisms affected
In patients with severe hepatic disease, both mechanisms of clearance are
affected and therefore the clearance of local anaesthetics is reduced
Does dose need to be changed for single shot
plasma levels do not differ after a
single dose of local anaesthetics due to
altered volume of distribution.
LAST with continious?
However, there is possibility of local
anaesthetic toxicity with
continuous infusions, and
doses must be reduced.
Liver blood supply
is there autoregulation present?
Liver has dual blood supply:
hepatic artery (25%) and portal system (75%).
Autoregulation is present in
hepatic arterial system,
but not in portal venous system
hepatic arterial buffer response
Hepatic artery alters its blood supply
depending upon portal venous
blood flow.
This is called hepatic arterial buffer response.
high level of neuraxial block
A high level of
neuraxial block is associated
with decrease in the portal blood flow,
but hepatic arterial blood flow is maintained
Diabetic patients Nerve stimulator
Diabetic patients usually have peripheral neuropathy and require higher stimulating current to locate nerves via nerve stimulator during peripheral nerve blockade.
Is there any affect on glucose control and outcome
Tight glucose control perioperatively is associated with improved
outcome in diabetic patients
Does RA Affect glucose levels at all?
Regional anaesthesia
prevents hyperglycaemic response
to surgery by various mechanisms:
inhibiting gluconeogenesis,
inhibiting catecholamine
and cortisol secretion
(prevents stress response to surgery).
regional anaesthesia in patients
with hypothyroidism
Any change to nerve
Thyroid neuropathy is common in hypothyroidism.
It is characterised by a delay in
conduction velocity on testing.
regional anaesthesia in patients
with hypothyroidism
Nerve stimulation difference?
Higher intensity of stimulating current
may be required to locate the
nerves via nerve stimulator during
peripheral nerve blockade.
Does hypothyroidism lead to any nerve deficits
Nerve entrapment is common –
median nerve (carpal tunnel syndrome)
and CNVIII involvement (deafness).
Double crush syndrome
There is increased risk of injury to nerves at one site if they are compressed or damaged at a different site.
Therefore, hypothyroid patients
with neuropathy are at higher risk of
neurological damage
following regional anaesthesia.
Trivial trauma with the needle during
block in patients can lead to
neurological deficits: this is called ‘double
crush syndrome’.
How can thyroid neuropathy be corrected?
Thyroxine helps in prompt
correction of neuropathy, thereby reducing
the risk of neurological injury.
most common injuries reported from anaesthesia are in the following order
Ulnar nerve injury >
brachial plexus injury >
lumbosacral nerve roots >
spinal cord.
Incidence of BP & Ulnar Nerve injury
> with GA vs Regional which?
Incidence of brachial plexus and ulnar nerve injury is more with general anaesthesia than with regional anaesthesia
Causes of neurological injury
In the majority of cases,
the cause of neurological injury is
ischaemia,
prolonged tourniquet time,
stretch,
direct trauma and haematoma
compressing nerve or interfering with its
blood supply
Mononeuropathy - whats safe
In patients with mononeuropathy,
both regional and general
anaesthesia are safe.
Parkinsonism is characterised
Parkinsonism is characterised by loss of
dopaminergic neurons in
substantia nigra
clinically manifesting
as tremor,
rigidity and
bradykinesia.
General anaesthesia & Parkinsonism
1
inhalational agents –
may accelerate autonomic instability
2
muscle relaxants, controlled ventilation –.
prolong post-operative ventilator support
3 opioids – exacerbate muscle rigidity, post-operative nausea and vomiting
4
increased incidence of post-operative cognitive dysfunction
Regional anaesthesia offers for parkinsonism
Regional anaesthesia offers:
better control of autonomic instability
avoidance of inhalation agents and muscle relaxants
less impairment of respiratory function.
Therefore, regional anaesthesia is always preferred over general
anaesthesia where feasible.
Multiple sclerosis (MS) what nerves affect
Multiple sclerosis (MS): involves only central nervous system
(brain and spinal cord)
and not the PNS.
It is associated with demyelination
in brain and spinal cord
MS
LP block
PVB
Lumbar plexus blocks and paravertebral blocks
may have a prolonged
duration of action due to
subarachnoid or epidural spread.
MS & PNB
Peripheral nerve block is safer where feasible.
MS & surgery
Patients with multiple sclerosis may
have a relapse
due to stress of surgery,
irrespective of type of anaesthesia they receive
Spinal shock
Acute spinal cord injury is associated with spinal shock.
There are four phases of spinal shock:
Stage 1: areflexia (0–1 days)
Stage 2: return of reflexes (1–3 days)
Stage 3: hyperreflexia (initial) (1–4 weeks)
Stage 4: hyperreflexia, spasticity (1–12 months
SCord injury acute phase ra vs ga
In the acute phase of spinal cord injury,
general anaesthesia is preferred because of:
1
the risk of airway compromise
2
haemodynamic instability
(relative contraindication for
regional anaesthesia)
3
the need for deep-vein thrombosis prophylaxis,
as there is a high risk
of thromoembolism.
Caution in GA ~>24h
However, succinylcholine use may
lead to hyperkalaemia if used after 24
hours,
because of proliferation of
extrajunctional nicotinic acetylcholine
receptors.
Chronic phase SC injury RA vs GA
chronic phase of spinal cord injury,
regional anaesthesia is
preferred because:
Autonomic dysreflexia is seen
after the resolution of acute phase of
spinal cord injury.
Autonomic dyreflexia @what level
what is it
It is seen when the level of injury is at or above
T7.
It is characterised by
extreme haemodynamic instability from
cutaneous or visceral
stimulation below the level of spinal cord injury.
Why is RA preferred in chronic injury
If the injury is below T7, the risk of autonomic dysreflexia is reduced.
Regional anaesthesia may be
used in chronic spinal cord injury, as it
prevents autonomic dysreflexia.
Myasthenia gravis is
Myasthenia gravis is an
autoimmune disease
characterised by weakness
and progressive fatiguability.
Myasthenia gravis
pathophys
There are antibodies against the
α-subunit of nicotinic ACh receptors
at neuromuscular junct
Myasthenia Gravis
Medical treatment
Medical treatment
includes
anticholinesterases,
steroids and
immunosuppressants
like cyclosporine, azathioprine,
plasmapheresis and
immunoglobulin
Surgical treatment
Myasthenia Gravis
Surgical treatment includes
thymectomy,
which can be done under
general anaesthesia or
thoracic epidural anaesthesia.
Quirk of Rx that must be checked before a form of anaesthesia MG
Full coagulation profile must be
obtained prior to regional anaesthesia,
as platelet function might be affected by steroids and
immunosuppressants
Is supraclav safe in MG
Bulbar and respiratory muscles
may be affected in myasthenic patients
hence supraclavicular blocks should be avoided.
Are all LA safe in MG?
Metabolism of ester local anaesthetics
is dependent on cholinesterase activity,
and therefore they are best avoided.
MG and opioids
Myasthenic patients have
increased sensitivity to opioids and
sedatives, and so these
should be used in low doses.
