8.1 Neurological Complications

Question 1

Regarding peripheral nerve injuries:

ga?

Most frequent nerve injured

Answer 1

Regarding peripheral nerve injuries:

Occur even with general anaesthesia
(without nerve block).

Ulnar nerve injury is the most frequent nerve injury

Question 2

Regarding peripheral nerve injuries:

Is stretching safe?

Answer 2

Stretching the nerve during peripheral nerve
block can lead to pressure injury
(as the connective tissue may be poorly compliant).

Question 3

Regarding peripheral nerve injuries:

needle bevel type

Answer 3

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.

Question 4

Regarding peripheral nerve injuries:

fascicle size

Answer 4

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.

Question 5

Risk factors for the development of nerve damage are as follows

Patient-related factors

Answer 5

Patient-related factors

male sex, 
elderly, 
very thin 
or very obese,
pre-existing diabetes 
or neurological damage.

Question 6

Risk factors for the development of nerve damage are as follows

Surgical factors:

Answer 6

Surgical factors:

infection, 
inflammation, 
vascular compromise,
tourniquet-induced ischaemia, 
stretch, positional and compression
injury

Question 7

Risk factors for the development of nerve damage are as follows
Anaesthetic factors:

Answer 7

Anaesthetic factors:

needle trauma
and local anaesthetic-
and
adrenaline- induced neurocytotoxicity

Question 8

mechanisms involved in
nerve injury

Mechanically injuries

Answer 8

laceration due to needle trauma,

stretch injury due to exaggerated positioning,

and
intraneuronal injections can lead to nerve damage.

Question 9

Lacerations sharp vs blunt

mechanisms involved in
nerve injury

Answer 9

Lacerations by sharp needles

(clear-cut wound) may be less injurious
than intrafascicular injections,

which may lead to extensive
disruption of fascicular architecture.

Question 10

mechanisms involved in
nerve injury

pain

paraesthesia

Answer 10

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.

Question 11

mechanisms involved in
nerve injury
Stim current 0.2mA

Answer 11

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.

Question 12

mechanisms involved in
nerve injury

Motor responses

stimulators?

Answer 12

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.

Question 13

Intraneural injection may be of two types

Answer 13

Interfascicular/extrafascicular:

Interfascicular:

Question 14

Interfascicular/extrafascicular:

nerve injury common

Answer 14

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.

Question 15

Interfascicular:

where

injury?

a/w

Answer 15

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).

Question 16

Classification of acute nerve injuries

Answer 16

Neuropraxia

Sunderland
class

Question 17

Neuropraxia

Sunderland
damaged
intact
fxn

Answer 17

Neuropraxia

1

Myelin damage

Most

Conduction delay

prognosis is best in neuropraxia and worst in neurotmesis.

Question 18

Axonotmesis

Sunderland
damaged
intact
fxn

Answer 18

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

Question 19

Neurotmesis

Sunderland
damaged
intact
fxn

Answer 19

Neurotmesis

5

Loss of axonal continuity
Endoneurium, perineurium
and epineurium damage

No layer intact

No conduction

Question 20

Local anaesthetics may have neurocytotoxic effects mediated via:

Answer 20

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.

Question 21

The cytotoxic potential is greater with:

Answer 21

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.

Question 22

Systemic toxicity potential hights

Answer 22

(although systemic toxicity
is in the order

tetracaine >
bupivacaine >
lignocaine

Question 23

Tourniquet-induced neuropathy

incidence

type

Answer 23

1
Incidence of 1 : 8000.

2
Varies in severity from neuropraxia
to permanent nerve damage.

Question 24

Tourniquet-induced neuropathy

Pressure

duration

Answer 24

Associated with higher than recommended pressures.

Duration of application should
not exceed 90–120 minutes without a
10- to 15-minute deflation period.

Question 25

Tourniquet-induced neuropathy

Bandages

Cuffs

Answer 25

Esmarch bandages may 
generate very high pressures immediately
under the bandage 
(so should be avoided as 
sole method of tourniquet).

Wider cuffs generate lower
pressures than narrow cuffs
(so are preferred).

Question 26

Optimal cuff inflation pressure in upper limb

Answer 26

Optimal cuff inflation pressure in upper limb is

‘LOP’ plus 50

Question 27

Optimal cuff inflation pressure in Lower limb

Answer 27

While in the lower limb it is ‘LOP’ plus 75 mmHg

Question 28

Limb occlusion pressure

Answer 28

Limb occlusion pressure (LOP) is the 
minimum pressure required to
stop the flow of arterial blood 
into the limb distal to the cuff. It may be
measured by a Doppler probe.

Question 29

Nerve blocks under heavy premedication or general anaesthesia

Patients may not be able to report pain ?

Answer 29

Pain is an unreliable indicator of nerve injury

Stopping injection after pain does not
prevent the development of nerve damage

‘Pressure paraesthesia’ is normal

Question 30

Nerve blocks under heavy premedication / GA

Premedication diminishes the patient’s
ability to report early indicators of local
anaesthetic toxicity?

Answer 30

Premedication has anticonvulsive actions which may
offer protection from local anaesthetic toxicity

With general anaesthesia, airway is already secured,
helping cardiopulmonary resuscitation should
cardiovascular problems develop

Question 31

Nerve blocks under heavy premedication / GA

Paediatric population

Answer 31

Paediatric population

Are regularly anaesthetised for blocks
Do not show greater risk of nerve damage than adults

Question 32

Recommendations to reduce the chance of nerve damage during a peripheral nerve block
(PNB)

Equipment:

Answer 32

Equipment:

Short-bevel/Tuohy needle less likely to
enter nerves than long-bevel

Use correct-length needles

Use pressure indicators (B-smart)

Accurate peripheral nervous system

Right probe for the given block (e.g.
high frequency for superficial blocks)

Ultrasound guidance vs peripheral
nervous system

Echogenic vs non-echogenic needles

Question 33

Recommendations to reduce the chance of nerve damage during a peripheral nerve block
(PNB)

Technique

Answer 33

Technique:

Strict asepsis

Advance needle slowly
(peripheral nervous system),

and only after identifying needle tip (ultrasound guidance)

Fractionation of injections

Avoid rapid injections

Avoid injections when unusual high pressures are required

Avoid injection when patient complaint of pain (always ask where and what kind of pain)

Avoid heavy premedication

Adequately experienced operator

Avoid repeating block

Question 34

Recommendations to reduce the chance of nerve damage during a peripheral nerve block
(PNB)

Drugs

Answer 34

Drugs:
Avoid high concentration of adrenaline
(1 : 400 000 than 1 : 200 000)
Lower-toxicity drugs (ropivacaine than
bupivacaine

Question 35

Recommendations to reduce the chance of nerve damage during a peripheral nerve block
(PNB)

patient

Answer 35

Patient:

Keep patient awake when you can

Question 36

Regarding nerve damage after a PNB:

duration afterblock

motor or sensory assesment

Answer 36

Regarding nerve damage after a PNB:

It usually presents after 48 hours
of recession of the block.

Motor loss is more informative than sensory loss in assessment of injury.

Question 37

Regarding nerve damage after a PNB:

first step

if this proves negative what next

Answer 37

First thing to do is to exclude
any vascular compromise
(arterial/venous).

A Doppler may be used to do this.

If such a compromise is found, surgical exploration may be needed.

If there is no vascular compromise,

then the next thing to do is to
obtain an evaluation by a neurologist

Question 38

Testing following a peripheral nerve injury

Test When and why

Nerve conduction study:

Answer 38

TABLE 8.4
Testing following a peripheral nerve injury

Test When and why

Nerve conduction study:
measures amplitude, time for signal
transmission and conduction velocity

Why? It helps to detect a nerve lesion

When? Within 1–2 days of nerve damage
Amplitude reduces in axonal injury
Velocity reduces in myelin damage

Question 39

Electromyography:

Answer 39

Electromyography:

measures muscle depolarisation

Why? It helps to locate a nerve lesion

When? From 2 to 4 weeks after nerve injury

Muscle defibrillation occurs 2–4 weeks after denervation

Question 40

High-frequency ultrasound

Answer 40

High-frequency ultrasound

Morphological changes in peripheral nerves
like nerve swelling, rupture, compression and so forth

Question 41

Magnetic resonance imaging

Answer 41

Magnetic resonance imaging

(neurography)

Demonstrates nerve anatomy and can reveal nerve
swelling, rupture or compression

It is the earliest method to detect nerve injury (24 hours

Question 42

What has the highest complication of the PNB

Answer 42

They noted

a higher complication rate with lumbar plexus block than other PNBs

Question 43

Neuraxial complication highest with

Answer 43

Spinal anaesthetics were more commonly associated with complications than epidurals or PNBs

Question 44

PNB block damage

Answer 44

Out of 12 patients with nerve damage subsequent to

PNB, blocks in nine were performed using a peripheral nerve stimulator.