Intraneural Injection Injury

Intraneural injection injury is damage to a nerve from injection of local anaesthetic into the nerve, either within the epineurium (extrafascicular, usually benign) or within the perineurium (intrafascicular, harmful).

Epidemiology. Intraneural injection is seen on ultrasound in a notable proportion of blocks without clinical harm (reports range widely). Persistent neurological deficit is rare, about 0.04% to 0.2%.

Risk factors. High injection pressure (over 20 psi), nerve stimulation at low current (under 0.2 mA), pain on injection, intrafascicular placement, short bevel needles, small nerve fascicles (interscalene), and neuropathy.

Pathophysiology.

Intrafascicular injection raises pressure within the fascicle, compromises endoneurial blood flow and ruptures the perineurium. High concentration local anaesthetic is neurotoxic, causing axonal loss and demyelination.

Severe pain or paraesthesia on injection, resistance to injection, persistent numbness, burning pain, weakness and sensory loss in the territory after the block should have resolved. Ultrasound may show nerve swelling during injection.

Red flags.

• Severe pain or paraesthesia on injection.
• Deficit persisting beyond 24 to 48 hours.
• Progressive motor weakness.

Clinical, with a record of injection events. Ultrasound for haematoma or nerve swelling, MRI for nerve oedema and nerve conduction with electromyography at 3 weeks for severity and prognosis. Exclude positional, surgical and tourniquet injuries.

Differential diagnosis.

• Surgical nerve injury.
• Tourniquet or positional neuropathy.
• Haematoma.
• Compartment syndrome.
• Pre-existing neuropathy.

Stop injecting at pain, resistance or visible nerve swelling, withdraw the needle by 1 to 2 mm and reposition. Document the event.

For a persistent deficit provide early documentation, ultrasound or MRI, electrophysiology at 3 weeks, protective care, physiotherapy and neuropathic pain treatment.

• Gabapentin: 300 mg orally, titrated every 3 days to 900 to 1,800 mg daily in three divided doses; maximum 3.6 g daily; monitor sedation and renal function; reduce in creatinine clearance under 60 mL/min.
• Amitriptyline: 10 mg orally at night, titrated to 75 mg; maximum 150 mg daily; monitor ECG and anticholinergic effects; avoid in recent myocardial infarction and arrhythmia.
• Steroids have uncertain benefit; a short course of prednisolone 40 mg orally once daily for 5 days has been used for acute inflammatory injury (maximum 60 mg daily; monitor glucose; avoid in uncontrolled infection).

Surgical exploration if no recovery at 3 to 6 months, and earlier for suspected transection.

Prevention. Ultrasound direction with needle tip visible, injection pressure monitoring (under 15 psi), stop on pain, use nerve stimulator thresholds (no motor response at under 0.2 mA), inject incrementally in 3 to 5 mL aliquots with aspiration, and keep the needle in the fascial plane around the nerve.

Monitoring. Neurological examination at 24 hours, 1 week and 4 weeks, repeated until recovery.

Referral and escalation. Neurology and peripheral nerve surgery. Disclosure and incident report.