Peripheral Nerve Injury After Regional Anaesthesia

Peripheral nerve injury after regional anaesthesia is a sensory or motor deficit in the distribution of a blocked nerve, persisting beyond the expected duration of the local anaesthetic. It arises from needle trauma, intraneural injection, local anaesthetic toxicity, ischaemia, pressure (tourniquet or position) or surgery.

Epidemiology. Transient symptoms occur in 3% to 15% of blocks (usually resolve within weeks). Persistent injury over 6 months occurs in about 0.04% (4 in 10,000) to 0.2% after peripheral blocks. Most deficits are caused by surgery or positioning rather than the block.

Risk factors. Diabetes, pre-existing neuropathy ("double crush"), peripheral vascular disease, chemotherapy, smoking, tourniquet time over 2 hours, high injection pressure, intrafascicular injection, high concentration of local anaesthetic, and adrenaline containing solutions.

Pathophysiology.

Mechanical injury, injection under pressure, ischaemia and neurotoxicity cause axonal or myelin damage. Seddon classification: neurapraxia (conduction block, recovery in days to weeks), axonotmesis (axon loss with intact sheath, recovery at about 1 mm daily), neurotmesis (complete disruption, needs surgery).

Numbness, paraesthesia, burning pain, weakness or paralysis in the nerve territory persisting after the block should have resolved (usually over 24 to 48 hours), and Tinel sign over the nerve.

Red flags.

• Severe pain on injection or paraesthesia during block.
• Progressive weakness.
• Tense swelling (haematoma, compartment syndrome).
• Deficit lasting over 48 hours.

Document the deficit and map it with examination. Use ultrasound to detect haematoma or anatomical injury. MRI for compressive lesions. Nerve conduction studies and electromyography at 3 weeks (earlier studies show denervation changes only after 10 to 14 days) establish the level, severity and prognosis. Exclude surgical causes and tourniquet or position injuries.

Differential diagnosis.

• Surgical nerve injury.
• Positional or tourniquet neuropraxia.
• Compartment syndrome.
• Haematoma.
• Cervical or lumbar radiculopathy.
• Stroke.

Early review within 24 hours of an unexpected deficit. Urgent imaging and surgical review if haematoma or compression is suspected.

Provide protection of the limb, physiotherapy to maintain range and prevent contracture, splints, and monitoring. Most injuries recover over weeks to 12 months.

• Gabapentin: 300 mg orally, increased 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, increased to 75 mg; maximum 150 mg daily; monitor ECG and anticholinergic effects; avoid in recent myocardial infarction and arrhythmia.

Exploration or nerve repair or graft is considered if no recovery at 3 to 6 months, and earlier for evidence of transection.

Prevention. Use ultrasound direction, stop injection with pain or resistance (opening pressure under 15 psi), avoid intraneural injection (visible swelling of the nerve), use the lowest effective concentration and volume, and check tourniquet times.

Monitoring. Neurological examination at 24 hours, 1 week, 4 weeks, 3 months and 6 months. Electrophysiology at 3 weeks.

Referral and escalation. Neurology, nerve surgery and pain service. Disclosure and incident report.