2. Peripheral nerve blockade (PNB) is associated with a number of potential
complications :
1. including inadvertent vascular puncture and associated haematoma
2.inadvertent damage to other structures
3.local anaesthetic systemic toxicity
4. infection
5.misplacement or migration of catheters
6. wrong-site block and nerve injury.
Introduction
3. Long Term Consequences of Nerve Injury
Although nerve injuries associated with PNB are often temporary, the
potential long-term consequences of nerve injury following PNB
include :
1. sensory and motor deficits
2.neuropathic pain
3. and permanent disability with an associated decrease in patient
quality of life.
4. Factors that may contribute to
peripheral nerve injury
Patient specific:
• pre-existing neurologic disorders,
• diabetes mellitus,
• extremes of body habitus,
• male gender, and advanced age.
Surgical risk factors:
• direct surgical trauma or stretch,
• compressive dressings or casts,
• tourniquet inflation,
• hematoma or abscess formation,
• perioperative inflammation
• Improper patient positioning.
5. Anatomy of Peripheral Nerve
• Peripheral nerves consist of axons bundled together by 3 separate connective
tissue layers.
• Most axons are myelinated, with a Schwann cell that covers the axon in myelin and
gaps known as the nodes of Ranvier spaced out at intervals to enhance nerve impulse
conduction.
• The axon and Schwann cell structure responsible for myelination is
termed the nerve fibre and is the functional unit of the peripheral nerve
complex.
• This is covered along the length of the fibre by the endoneurium, the innermost
connective tissue layer that contributes to the specialised environment
that protects the axons.
• Nerve fibres are then grouped together into fascicles surrounded by the
perineurium, which acts as the principle protective layer of the axon.
• Fascicles are bundled into peripheral nerves, surrounded by an outer layer called the
epineurium.
6.
7.
8. Clinical Classification of Nerve Injury
• Seddon Classification:
Neuropraxia
Axonotmesis
Neurotmesis
Sunderland classification:
Proposed a five-grade classification
system.
12. Pathophysiology of Nerve Injury
Most Common pathophysiology includes:
1. mechanical injury (either through direct trauma of the needle or
pressure effects)
2. toxicity of injectate
3. inflammatory injury
4. ischaemic injury
13. Mechanical injury
• Mechanical injury may occur via direct needle trauma or peripheral
nerve catheter placement.
• Disrupting the perineurium can lead to direct axonal injury or
fascicular content leakage and loss of the protective
environment, which can subsequently expose axons to higher
concentrations of local anaesthetic (with associated toxicity).
• There can also be some localised cellular and inflammatory changes.
14. Another deleterious effect related to the lack of perineurial compliance
is increased pressure on the injection, which leads to disruption of
blood supply and ischaemia.
15. • Mechanical injury risk also differs according to the site of injection
due to differing neural to connective tissue ratios. Having relatively
more connective tissue decreases the possibility of a needle
entering a fascicle itself.
• Even if a needle penetrates a nerve, the fascicles are more likely to
be pushed out of the way, decreasing the risk of intraneural injection,
whilst having more neural tissue and less connective tissue increases
the risk of fascicular injury.
16. Relative differences between neural and connective tissue. Note in (A) the relative abundance of connective
tissue, so that the needle is more likely to miss the neural tissue and push the neural tissue aside.(B) there is a
higher neural to connective tissue ratio, so fascicular penetration is more likely, with associated PNI
17. Toxicity
• All local anaesthetics used in clinically relevant concentrations can be
potentially neurotoxic.
• A number of pathophysiological processes have been postulated, from
vasoconstriction to mitochondrial disruption, although the effect is
dose dependent.
• The site of local anaesthetic administration is the most important factor
for toxicity, with intrafascicular injection leading to more injury than intra-
or extraneural injections. The addition of adjuncts may also play a
role in neurotoxicity (eg, adrenaline may disrupt neural blood
flow).
19. Ischaemic Injury
• Local or diffuse ischaemia occurs either from direct occlusion by acute
haemorrhage or via direct vascular injury, both of which can disrupt
neural vascular supply.
• About 50% of a peripheral nerve’s vascular supply comes via the
network of capillaries known as the vasa nevorum.
• This means that disruption should localise (and minimise) damage, with
the remaining collateral blood supply aiding perfusion, as no single vessel
dominates perfusion.
20. • As mentioned previously, local anaesthetics and their
adjuncts may affect vascular supply, as can trauma, high
injection pressure, tourniquets, or extra- or intraneural
haematomas.
21. Inflammatory Injury
• Inflammatory injury is being increasingly recognised as playing a role
in some PNB-related neuropathy
• for example, nonspecific inflammatory responses have been
suggested as the mechanism of chronic diaphragmatic paralysis
following interscalene block, resulting in adhesions, fascial
thickening, vascular changes, and scar tissue compressing the nerve.
• Intraneural injection of ultrasound gel has also been implicated in
inflammatory changes
22. Site Specific Risks
UPPER EXTREMITY
Horner’s syndrome : myosis-ptosis-anhidrosis
Recurrent laryngeal nerve involvement: Induce hoarseness
Vertebral artery involvement: Induce seizures
Pneumothorax : Close proximity of pleura
Phrenic paresis
Epidural injection
23.
24.
25.
26. Site Specific Risks
Lower Extremity Risks
1. Injury to extremity
2. Fall/weakness
3. Epidural spread
32. How to avoid nerve injury
1. Never inject local anesthetic when abnormal
pressure on injection is present.
2. Never inject when patient complains of severe pain
or has a withdrawal reaction.
3. Never inject when there is abnormal resistance.
33. Choice of Needle
• Bevel type and needle size are important determinants of nerve damage.
Sharp long-bevelled (12-15degree angle) needles are more likely to
pierce the perineurium
• whereas blunt short- bevelled (45-degree angle) needles may allow
fascicles to slide away from the needle, potentially reducing neural injury.
• However, if short-bevelled needles penetrate the perineurium the
extent of mechanical trauma far exceeds that produced by a
long-bevelled needle. The degree of damage is also directly
proportional to needle gauge, with larger gauge needles markedly
increasing fascicular damage
34. Paraesthesia
Severe paraesthesia or pain on needle advancement or injection may
imply intraneural placement. So as to preclude any potential
further injury, the clinician should stop and either reposition the needle
and/or stop injecting.
Factors such as sedation, comorbidities (eg, peripheral neuropathy),
the patient’s ability to communicate or perceive pain, and sensory
blockade from local anaesthetic already present can affect evaluation
of paraesthesia.
35. Peripheral Nerve Stimulation
Most authors suggest a current intensity between 0.2 to 0.5 mA
indicates a needle- to- nerve position that is sufficient for safe
placement of local anesthetics.
If a motor response is obtained with a current less than 0.2mA,it is
highly specific for intraneural needle placement, and the needle should
be repositioned.
36. Injection Pressure Monitoring
• Pressure monitoring is considered highly sensitive for intra- fascicular
intraneural injection but lacks specificity.
• Lots of studies are still going on but evidence is still limited so far.
• Avoidance of high injection pressure >15psi is likely to
improve the safety and be clinically justifiable.
37. Ultrasound
• US has many advantages including:
• reduced dose and volume of LA required
• decreased intravascular puncture. and
• incidence of local anaesthetic systemic toxicity (LAST)
38. Evaluation of Nerve Injury after
Regional Anesthesia
• History
• Physical Examination
• Electrophysiologic studies (EMG, nerve
conduction studies)
• Radiographic studies
