American Society of Regional Anesthesia and Pain Medicine August 2016 - 22
PATHOPHYSIOLOGY
Nerve injury after PNB is usually due to mechanical, vascular, or
chemical causes. When these causes are not related to postoperative
neuropathy, inflammatory causes should be considered.
nerve blood supply.4 Increased connective tissue in nerves provides
protection to these vessels; thus, more distal nerves are less prone
to ischemic injury.3 Vessel puncture can lead to hematoma formation,
while large hematomas result in compression, leading to injury.3
Mechanical Injury. Compression of nerves by forceful needlenerve contact or intraneural injection can be deleterious.2
Prolonged mechanical compression as from a hematoma leads to
focal demyelination.2 Intrafascicular injection of local anesthetic
increases intraneural pressure, compressing vasculature and
leading to ischemia.3
Local anesthetics can alter vascular supply to nerves but not as
significantly as epinephrine. The two medications act synergistically
to reduce neural blood flow by 60%.5 Nerve injury resulting from
injection of local anesthetic-epinephrine versus use of only local
anesthetics is unclear.5
Severe nerve damage can occur with forceful intrafascicular
injection. Rupture of the perineureum can lead to severe myelin
and axonal degeneration.3 While intrafascicular injection of local
anesthesia can cause toxic injury, damage is also possible with
intrafascicular injection of saline.3
Vascular Injury. Neural ischemia may result from disruption of
the vascular supply to the nerves. Epineural vessels supply 50% of
22
2
Chemical Injury. All local anesthetics have neurotoxic effects;
however, their potential for damage varies.3 Increased exposure
of the nerve to local anesthetic and concentration of local
anesthetic leads to greater death of Schwann cells and myelin
damage.6 Intrafascicular injection of local anesthetic is the primary
determinant of neurotoxicity.7 In rodent models, intrafascicular
injection leads to demyelination and axonal and Wallerian
degradation, while extrafascicular injection is associated with less
severe abnormalities.7
American Society of Regional Anesthesia and Pain Medicine
2016
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