Peripheral Nerve Injury from Regional Anesthesia

Basic Concepts, Risk Factors, and Causes

• The anatomy of a peripheral nerve consists of multiple layers, which contain connective tissue, blood vessels, adipose tissue, and bundles of individual nerve fibers that are further encased in protective layers.
• Protective layers that encase different levels of a peripheral nerve include the epineurium, perineurium, and endoneurium.

• Risk factors associated with peripheral nerve injury during regional anesthesia include type of nerve block performed, patient body habitus, presence of prior neuropathy, coagulopathy or use of anticoagulation medications, intraneural injection, local anesthetic toxicity, neuronal ischemia, trauma to the nerve (i.e. needle trauma), pressure injury (patient positioning, cast or dressing application), perineural infection, or surgical injury.¹
• Patient history of smoking and diabetes (especially those with diabetic neuropathy present) has been shown to have an increased risk of peripheral nerve injury during regional anesthesia.
• Causes of peripheral nerve injury during regional anesthesia can be defined as mechanical, chemical, or vascular.²
  • Mechanical damage occurs when the injection of the local anesthetic is performed within the epineurium, and high pressure of the local anesthetic within this area causes damage to the blood vessels/nerve bundles.
  • The type and gauge of needle used that penetrates the epineurium increases the risk of nerve damage.
    • Short bevel blunt needles have more difficulty penetrating the epineurium.
    • Long bevel needles can penetrate the epineurium more easily than short bevel needles, and thus the use of these needles during nerve blocks increases the risk of neuronal injury.
  • Chemical damage is determined by the location of placement of local anesthetic; if local anesthetic is distributed within the epineurium, it can cause axonal damage/demyelination of axons.
  • Perineural injection with adjuncts such as epinephrine or clonidine (which will prolong the duration of the nerve block) could increase the risk of nerve damage in patients with prior vascular compromise (diabetics, smokers) due to prolonged vasoconstriction surrounding the nerve.
  • Vascular damage occurs when there is compression of the blood supply to the nerve (via hematoma formation or volume of local anesthetic) or there is actual injury to the vasa nervorum during nerve block placement.
• Other causes of peripheral nerve injury in the perioperative period can be attributed to positioning or surgical disruption.
  • Proper positioning in the perioperative environment is essential to prevent nerve damage/injury and pressure injuries.
  • The most commonly injured nerve by improper positioning is the ulnar nerve, followed by the common peroneal nerve.
  • See the OA summary on peripheral nerve injuries from positioning for more details. Link
  • Surgical disruption occurs when the nerves are cut, stretched, or entrapped.
    • Nerves may be intentionally or unintentionally severed during surgical dissection which would result in loss of sensory or motor function.
    • Patients may experience neurologic dysfunction after certain procedures, particularly those that require the use of retractors (e.g., hypoglossal nerve and carotid endarterectomy secondary to superior incision retractor placement).
    • Nerves can become entrapped secondary to increased pressure within fascial compartments (compartment syndrome), tight dressings or casting, or accidental trapping within a joint or fracture reduction site.

Types of Nerve Injury

• Nerve damage can range from mild with sensory deficits to severe with combined sensory and motor deficits. It can last from days to potentially years, depending on the degree of nerve damage.³
• The types/degree of nerve damage are described as neurapraxia, axonotmesis, and neurotmesis.

Diagnosis of Peripheral Nerve Injury

• Early detection and intervention may prevent prolonged damage depending on the type of deficit.
• While symptom recognition may be challenging, as many patients are in the outpatient setting postoperatively, it is essential to counsel patients receiving regional anesthesia on monitoring for the resolution of block symptoms within 48 hours of block onset.
• If symptoms persist, early notification of failure of block resolution is key for accurate diagnosis, treatment, and a better prognosis.
• Symptoms include, but are not limited to, abnormal sensation (i.e., difficulty determining temperature in the affected area), loss of motor function, hyperalgesia, paresthesia, pain, and allodynia.⁶
• Small nerve fibers are more susceptible to damage and, if damaged, are likely to cause paresthesia.
• After reporting non-resolution of block symptoms, a physical exam should be performed as soon as possible to determine if symptoms are related to the surgical procedure, regional anesthesia technique, etc., to allow for the initiation of interventions to reduce long-term damage or loss of function.
• A referral to a neurologist or specialist in neurologic injury should be made as soon as possible so further investigation can take place.
• Both imaging and NCT can aid in diagnosing peripheral nerve injury after regional anesthesia.²
  • Imaging may include both ultrasound and magnetic resonance imaging (MRI).
    • Ultrasound can be used to evaluate for a hematoma or other fluid collection that could contribute to nerve compression (i.e., seroma).
    • MRI is used for evaluation of surrounding soft tissue damage contributing to nerve compression, muscle atrophy secondary to denervation, and for surgical planning (if applicable).
  • NCT
    • NCTs include both NCS and EMG, and are used to measure the amplitude and latency of nerve conduction through a specific/targeted muscle or sensory nerve, which helps determine if the targeted nerve has been injured and to what degree.²
    • NCTs can also help determine if a preexisting nerve injury existed prior to the regional anesthetic or the surgical procedure.
    • These tests can determine if the injury is secondary to loss of myelination or axons and can be further used over time to assess whether regeneration in the damaged nerve distribution is occurring.
    • NCS
• NCS assess motor/sensory (or both) nerve function.
• NCS examines the amplitude and latency of targeted nerves, which can help determine if nerve damage is present, whether the damage is related to axonal or myelin sheath injury, and whether the injury is generalized or focal.²
  • EMG
• EMG assesses only motor function by stimulating the muscle directly and measuring muscle excitability and contractions.

Treatment of Peripheral Nerve Injury

• Initial treatment of peripheral nerve injury may include supportive medical therapy, including rest, medications to treat pain (including neuropathic pain management), and corticosteroids for suspected perineural inflammation.^4,5
• After an appropriate evaluation and diagnosis, early physical and occupational therapy may be beneficial in strengthening and preserving function in the affected limb.
• Care coordination among physical and occupational therapists, neurologists, and surgeons is crucial in facilitating timely interventions to preserve as much neurologic function as possible, while also maintaining an appropriate quality of life for the patient.
• If the nerve damage is severe and prolonged, surgical intervention may be required. Depending on the extent of damage and imaging results, surgical interventions may include decompression of the affected nerve (i.e., hematoma evacuation if a hematoma is present), resection of perineural scar tissue that may have formed, direct repair of damaged nerve fibers, or complete nerve grafting to reinnervate the affected area.

Strategies to Reduce the Risk of Peripheral Nerve Injury During Regional Anesthesia

• Careful screening of the patient’s previous medical history, including a thorough neurologic exam and evaluation of any underlying neuropathies, should be conducted preoperatively prior to any administration of regional anesthesia. Additionally, an extensive discussion of the risks and benefits of performing regional anesthesia should be had with the patient prior to performing the block. A physical examination of the area where the nerve block will be performed should be completed prior to administering the nerve block, specifically looking for sensory or motor deficits in the limb that will be affected and signs of infection.
• Performing the peripheral nerve block under ultrasound guidance with complete needle visualization and visualization of anatomic structures, including the nerve targets and any blood vessels located in the area, has been shown to decrease the risk of intraneural or intravascular injection of local anesthesia.³
• Selecting the appropriate local anesthetic volumes for each block and patient is crucial in reducing the risk of peripheral nerve injury.
• Care in the use of adjuvants (epinephrine, clonidine, dexamethasone) should be taken, especially in patients with risk factors that may increase the risk of peripheral nerve injury (diabetes, smoking, prior neuropathy).
• Listening to feedback from the patient while performing regional anesthesia (if the block is being performed awake) can help determine the proximity of the needle and local anesthetic deposition to the targeted nerve.
• Careful positioning in the operating room during a surgical procedure can help reduce the incidence of peripheral nerve injury.³