8.1 Neurological Complications Flashcards
(44 cards)
Regarding peripheral nerve injuries:
ga?
Most frequent nerve injured
Regarding peripheral nerve injuries:
Occur even with general anaesthesia
(without nerve block).
Ulnar nerve injury is the most frequent nerve injury
Regarding peripheral nerve injuries:
Is stretching safe?
Stretching the nerve during peripheral nerve
block can lead to pressure injury
(as the connective tissue may be poorly compliant).
Regarding peripheral nerve injuries:
needle bevel type
Shorter-bevel needles
push the nerve away
rather than cut it
(like long bevel needles),
but should an intraneural
injection occur, subsequent
nerve injury can be much worse.
Regarding peripheral nerve injuries:
fascicle size
Larger fascicle size makes the nerve more prone to damage, as it can accommodate the tip of the needle and an intraneural injection can occur.
Risk factors for the development of nerve damage are as follows
Patient-related factors
Patient-related factors
male sex, elderly, very thin or very obese, pre-existing diabetes or neurological damage.
Risk factors for the development of nerve damage are as follows
Surgical factors:
Surgical factors:
infection, inflammation, vascular compromise, tourniquet-induced ischaemia, stretch, positional and compression injury
Risk factors for the development of nerve damage are as follows
Anaesthetic factors:
Anaesthetic factors:
needle trauma
and local anaesthetic-
and
adrenaline- induced neurocytotoxicity
mechanisms involved in
nerve injury
Mechanically injuries
laceration due to needle trauma,
stretch injury due to exaggerated positioning,
and
intraneuronal injections can lead to nerve damage.
Lacerations sharp vs blunt
mechanisms involved in
nerve injury
Lacerations by sharp needles
(clear-cut wound) may be less injurious
than intrafascicular injections,
which may lead to extensive
disruption of fascicular architecture.
mechanisms involved in
nerve injury
pain
paraesthesia
Pain on injection is an
unreliable indicator of intraneural injections.
Paraesthesia may not be a
risk factor for nerve damage,
and stopping injection upon
paraesthesia may not reduce the chances
of ensuing nerve damage.
mechanisms involved in
nerve injury
Stim current 0.2mA
Stimulating currents less than 0.2 mA
are associated with a higher
chance of needle tip lying
within the nerve.
Hence injections should be made
within a range of 0.2–0.5 mA.
mechanisms involved in
nerve injury
Motor responses
stimulators?
Motor responses may not
always be seen with stimulation.
They may be absent even
when the needle tip is within the nerve itself!
Hence nerve stimulators may
not prevent nerve injuries.
Intraneural injection may be of two types
Interfascicular/extrafascicular:
Interfascicular:
Interfascicular/extrafascicular:
nerve injury common
when the injection is within the nerve,
but between the fascicles of the nerve.
This may be more common,
and
the developing block
may be faster than usual and
prolonged in duration.
Neural injury may not develop secondary to
interfascicular injections.
Interfascicular:
where
injury?
a/w
when the injection is made
within the nerve,
and
within a fascicle.
This disrupts the fascicular
architecture and leads to extensive injury.
This may be accompanied by pain, paraesthesia and difficulty in injecting (pressures exceeding 20 psi).
Classification of acute nerve injuries
Neuropraxia
Sunderland
class
Neuropraxia
Sunderland
damaged
intact
fxn
Neuropraxia
1
Myelin damage
Most
Conduction delay
prognosis is best in neuropraxia and worst in neurotmesis.
Axonotmesis
Sunderland
damaged
intact
fxn
Axonotmesis
2
Loss of axonal continuity
Endoneurium, perineurium
and epineurium intact
No conduction
3
Loss of axonal continuity
Endoneurium damaged
Perineurium and
epineurium intact
No conduction
4
Loss of axonal continuity
Endoneurium and
perineurium damaged
Only epineurium intact
No conduction
Neurotmesis
Sunderland
damaged
intact
fxn
Neurotmesis
5
Loss of axonal continuity
Endoneurium, perineurium
and epineurium damage
No layer intact
No conduction
Local anaesthetics may have neurocytotoxic effects mediated via:
Local anaesthetics may have
neurocytotoxic effects mediated via:
1 -
mitochondrial damage leading to loss of
adenosine triphosphate production,
accumulation of intracellular calcium,
activation of caspaces and
ensuing apoptosis
2
blockade of axonal transport
3
disruption of cell membranes.
The cytotoxic potential is greater with:
The cytotoxic potential is greater with:
1
lignocaine and tetracaine
than bupivacaine
2
addition of epinephrine
3
higher concentration of local anaesthetic
4
prolonged exposure
5
nerve stretching
6
pre-existing neurological condition
(‘double crush syndrome’)
7
intrathecal use rather than
epidural or peripheral use.
Systemic toxicity potential hights
(although systemic toxicity
is in the order
tetracaine >
bupivacaine >
lignocaine
Tourniquet-induced neuropathy
incidence
type
1
Incidence of 1 : 8000.
2
Varies in severity from neuropraxia
to permanent nerve damage.
Tourniquet-induced neuropathy
Pressure
duration
Associated with higher than recommended pressures.
Duration of application should
not exceed 90–120 minutes without a
10- to 15-minute deflation period.
