Nerve Injury

• Incidence of nerve injury after regional or neuraxial anaesthesia is difficult to establish, owing to:
• The rarity of its occurrence
• Heterogenous definitions and reporting
• Limited, and poor quality, evidence base
• Difficulty differentiating between RA-associated nerve injury and other causes e.g. positioning, surgical trauma


• Post-operative neurological symptoms, i.e. persistent paraesthesia, occur in 8 - 15% but rarely goes on to because a permanent injury
• Transient, reversible symptoms <7 days: up to 3%
• By 4-6 weeks: <5% still affected
• By 3 months: ≤2.2% still affected
• By 6 months: ≤0.8% still affected
• By 1 year: 0.03 - 0.2% still affected


• The incidence of nerve injury is somewhat dictated by the surgical intervention:

• Overall the risk of permanent nerve injury from regional anaesthesia is extremely low: 0.01 - 0.04%
• Non-regional anaesthetic causes of nerve injury are significantly more common

• Mechanical
• Partial or complete laceration
• Forceful contact from needle (nerve block, Tuohy or spinal)
• Intraneural injection
• Involves breech of the protective epineurium and perineurium, exposing individual nerve fascicles to either direct trauma or other toxins


• Pressure
• Acute LA injection in a confined space
• Chronic extrinsic compression of the nerve ± its vascular supply
• Typically causes a neurapraxia, where the myelin sheath is stretched but the axon is preserved


• Chemical
• LA-induced chemical neurotoxicity
• Other toxic substances e.g. alcohol, phenol, chlorhexidine
• The damage is dependent on the duration and concentration of LA the fascicle is exposed to


• Vascular
• Due to high intraneural pressure exceeding capillary pressure, leading to nerve ischaemic
• Direct trauma to vasculature during block
• Haematoma formation from vascular puncture
• Reduced blood flow due to LA and/or adjuncts

• The Seddon classification defines nerve injury based on the degree of axonal disruption:


• Neuropraxia
• Damage limited to myelin sheath
• Typically from nerve stretch or compression
• Recovery in weeks-to-months


• Axonotmesis
• Loss of axonal continuity but intact endoneurium
• Recovery prolonged and/or incomplete depending on the injury


• Neurotmesis
• Complete nerve transection
• Requires surgical intervention
• Poorest prognosis

• Amide local anaesthetics are less neurotoxic than ester local anaesthetics
• Ropivacaine has the lowest potential for neurotoxicity
• Levobupivacaine has the lowest potential for LA-mediated vasoconstriction (lidocaine the greatest)


• If adrenaline is added use low dose (<1 in 200,000); above this there is dose-dependent reductions in blood flow
• Avoid unlicensed use of perineural adjuncts where possible, although commonly used adjuncts are not known to be neurotoxic

• Use blunt, short-bevelled (45° angle) needles preferentially as they are less likely to puncture the nerve fascicle
• They will cause a greater degree of trauma if they do puncture it, however


• Use a smaller needle gauge
• Use an echogenic needle
• Use a tangential approach i.e. do not aim needle straight at the nerve
• Use NRFit needles to reduce risk of wrong-route drug administration

• An awakem responsive patient is recommended by consensus guidelines and is considered the gold standard
• The absence of pain or paraesthesia during needling or injection does not,however, eliminate the risk of nerve injury
• Can help identify early local anaesthetic systemic toxicity
• Blocks in paediatric practice are performed almost universally in asleep patients without significantly increased prevalence of nerve injury

• Paraesthesia during the block is not a reliable indicator of nerve contact
• The absence of paraesthesia does not exclude peripheral nerve injury
• The presence of paraesthesia increases the likelihood of transient neurological symptoms
• If paraesthesia is present it should lead to needle repositioning

• However:
• Ultrasound is unnable to distinguish between inter- and intra-fascicular needle-tip location
• Does not reduce incidence of neuraxial complications
• Does not reduce the incidence of permanent nerve injury associated with RA
• Perceived superior safety from in-plane needling technique is not substantiated in the literature and an out-of-plane technique may be equally safe
• Robustly visualised LA spread around the nerve can reduce time to onset of block and efficacy, at the expense of multiple needle manipulations and therefore trauma

• Does not predict needle tip to nerve location as accurately as one might think
• A motor response at a current of <0.2mA is highly specific, but not sensitive, indicator of intraneural needle placement
• Nerve puncture and mechanical injury may have already occurred
• Prevents further injury from LA injection
• Use of a nerve stimulator with current 0.2 - 0.5mA and a pulse duration 0.1ms indicates a needle-to-nerve position that is sufficient for accurate and safe placement of LA

• 'Syringe-feel' is highly inaccurate
• Objective pressure monitoring is highly sensitive, but poorly specific, for intrafascicular injection


• A low opening pressure (<15psi = 100kPa) is indicative of extra-fascicular and extra-neural injection
• However, intraneural extrafascicular injection may have a low opening pressure due to the compliance of the compartment


• A high opening pressure is indicative of either intraneural intrafascicular injection or needle-tip obstruction e.g. abutting structure

• If suspected nerve injury has occurred, take a thorough history and examination to establish presence of clinical features:
• New onset pain
• Motor weakness or altered sensation (inc. paraesthesia) lasting beyond the usual duration expected from the block performed
• Need to exclude sinister causes e.g. infection, haematoma, other space-occupying lesion
• Sometimes features only become apparent days-to-weeks post-block

• Reassurance
• Safety netting
• Arrange follow-up for ∽4 weeks' time


• Those whose symptoms have abated at that time can be discharged
• Those with persistent symptoms should have:
• Neurology referral
• Consideration of investigations such as MRI, nerve conduction studies or electromyography

• Review by senior members of the Surgical team (e.g. is there surgical injury or cause which needs intervention) and Anaesthetic team
• Further imaging
• Immediate Neurology referral
• Nerve conduction test - localise site of conduction block within a nerve
• EMG - determine muscle units affected by the injury

• No demonstrable benefit from any pharmacological agents with respect to nerve regeneration
• Anti-neuropathic analgesia may help if there is neuropathic pain present
• Referral to specialist peripheral nerve surgeon if long-term, non-improving deficits
• Physiotherapy to maintain muscle mass and avoid contractures