Safety aspects

Chris Nixon


Basic rules:


1. Keep it simple
2. Use minimum number of needle passes
3. Aim to miss nerve
4. Ask “How can I stay away from the nerve”
5. STOP before you block – Ensure correct patient, side, site, drug
        WHO sign-in
        Confirm patient identity and consent form
        STOP moment immediately before needle insertion:
        Anaesthetist and assistant to confirm
        Surgical site marking
        Side of the block


Sites(1) observed 398 errors committed by novices during the performance of 520 blocks.  

        Failure to visualise needle before advancement
        Unintentional probe movement
        Failure to recognise maldistribution of LA
        Failure to recognise IM location of needle before injection
        Fatigue (often due to poor patient positioning and poor ergonomics)
        Failure to correlate sidedness of patient and image
        Poor choice of needle insertion site and angle

Intraneural injection

Following the publication by Bigeliesen(2) of frequent inadvertent intraneural injection there has been continuing debate about what it is, whether it is associated with nerve injury, how to prevent it, and whether it may be useful.
The only agreement refers to subperineural injection which should be avoided due to its association with damage to the nerve fibres.  What steps can we take to reduce this risk?

Nerve stimulation

has long been suggested to be able to identify whether the needle lies within a nerve based upon the reported relationship between the depolarization threshold current and the distance between nerve and needle first reported by Pither.  Low current nerve stimulation (0.1-0.4mA) is predictive of a close needle to nerve distance but, in some anatomical locations it may signal intraneural placement.  This makes the use of a low stimulating current (0.2-0.3mA) unreliable as a prediction of intraneural placement since nerves vary in their stimulating threshold. Diabetic nerves usually have a higher threshold. Absence of a motor response also does not preclude needle placement. Additionally it has been shown that needle trauma can create oedema or introduce blood, which act as conductive solutions, decreasing the conductive area, and increasind the stimulation threshold(3).  Nerve stimulator output is also not always reliable(4).

Pressure monitoring.

Hadzic(5) demonstrated an association between injection pressure and intraneural needle placement.  This has been also shown by Orebaugh(6) in cadavers where the deliberate injection of brachial plexus nerve roots was associated by pressures between 25 and 50psi, all roots also showing expansion in cross sectional area by 45% after 5ml were injected.  More recently, Gadsden was able to demonstrate high opening pressures when a needle contacted the femoral nerve during fascia iliaca/femoral nerve block.  Can we reliably detect this?  Subjective sensation of pressure is not 100% reliable and therefore injection pressure monitors have been developed and are available commercially.  A simple technique described by Ban Tsui relies on the relationship of volume of air and pressure. By adding some air (2-4ml) to the syringe of LA, a halving of the volume indicates a doubling of pressure to 15 psi above atmospheric.


Vincent Chan(7,8) demonstrated that intraneural injection is associated with nerve swelling.  Ultrasound is capable of visualizing the needle tip and its closeness to the nerve.  So how close does the needle need to be.  For interscalene block the needle can be as far as 6mm from the nerve, but essentially the disposition of local anaesthetic is the important determinant.  As the needle approaches the nerve small test injections may be used to assess whether the local distribution will result in nerve blockade.  The needle then need be advanced no further.  Many blocks are placed in fascial planes or in a perivascular manner where the nerve itself is not targeted.


Often added to increase block duration but also able to reduce the blood supply to peripheral nerves.  Adrenaline has been shown to worsen nerve injury in animal models although the clinical relevance of this is unknown.  It has been used for many years during which time long term nerve injury has been documented at an incidence of 4 per 10,000(9).


There is no reliable data on the injury risk of other adjuvants e.g Clonidine, Buprenorphine, dexamethasone


Neurotoxicity of local anaesthestic drugs(10).

  1. Evidence of undesirable side effects
  2. Interaction with different targets
  3. Effects seen on nerves and myocytes
  •            Change in Ca++ mobilization
  •            Effects are time and concentration dependent
  •            Toxicity prevention is based on determination of the minimum low concentration for different blocks
  •            Anti-oxidants may be protective
  •            Liposomal preparations which prolong duration require further investigations into their effects


PRACTICAL TIPS to reduce Local Anaesthetic Toxicity

Ultrasound may reduce incidence(11)
       Always aspirate before injection
       Fractionate injections
       Slow injections safer
       If on injection there is no appearance of LA then STOP and assume intravascular injection – MOVE needle.
       Have Intralipid 20% available(12)
       Monitor for CNS and CVS toxicity


Management of LAST  From Royal College of Anaesthetists  UK

Care of the Insensate limb.

Following the initiation of a block, attention should be given to the insensate or weak limb.
      Pressure area care to prevent neuropathy
      Non weight bearing for limb or a leg brace for Quadriceps weakness
      Sling for upper limb
      Consider analgesia for pain after recovery from nerve block
      Avoid heat, pressure etc near numb area



1. Sites BD, Spence BC, Gallagher JD, Wiley CW, Bertrand ML, Blike GT. Characterizing novice behavior associated with learning ultrasound-guided peripheral regional anesthesia. Regional Anaesthesia and Pain Medicine. 2007 Mar;32(2):107–15.
2. Bigeleisen PE. Nerve Puncture and Apparent Intraneural Injection duringUltrasound-guided Axillary Block Does Not InvariablyResult in Neurologic Injury. Anesthesiology. 2006 Sep 16;105:779–83.
3. Klein SM, Melton S, Grill WM, Neilsen KC. Peripheral nerve stimulation in regional anaesthesia. Regional Anaesthesia and Pain Medicine. 2012 Jun 17;37(4):383–92.
4. Hadzic A, Vloka J, Hadzic N, Thys DM. Nerve Stimulators Used for Peripheral Nerve Blocks Vary in Their Electrical Characteristics. Anesthesiology. 2003 Mar 8;98:969–74.
5. Hadzic A, Vloka JD, Claudio RE, Hadzic N, Thys DM, Santos AC. Electrical nerve localization: effects of cutaneous electrode placement and duration of the stimulus on motor response. Anesthesiology. 2004 Jun;100(6):1526–30.
6. Orebaugh SL, Mukalel JJ, Krediet AC, Weimer J, Filip P, McFadden K, et al. Brachial plexus root injection in a human cadaver model: injectate distribution and effects on the neuraxis. Regional Anaesthesia and Pain Medicine. 2012 Sep;37(5):525–9.
7. Abdallah FW, Chan VWS. Monitoring intraneural needle injection: work in progress. Anesth Analg. 2014 Mar;118(3):504–6.
8. Brull R, Chan VWS, McCartney CJ, Perlas A, Xu D. Ultrasound detects intraneural injection. Anesthesiology. 2007 May 10;106(6):1244.
9. NEAL J. Effects of epinephrine in local anesthetics on the central and peripheral nervous systems: Neurotoxicity and neural blood flow. Regional Anaesthesia and Pain Medicine. 2003 Mar;28(2):124–34.
10. Nouette-Gaulain K, Capdevila X, Rossignol R. Local anesthetic “in-situ” toxicity during peripheral nerve blocks: update on mechanisms and prevention. Curr Opin Anaesthesiol. 2012 Oct;25(5):589–95.
11. Barrington MJ, Kluger R. Ultrasound guidance reduces the risk of local anesthetic systemic toxicity following peripheral nerve blockade. Regional Anaesthesia and Pain Medicine. 2013 Jul;38(4):289–97.
12. Nouette-Gaulain K, Capdevila X, Robin F, Beloeil H. [Intravenous lipid emulsion and local anesthetic-induced systemic toxicity: mechanisms and limits]. Ann Fr Anesth Reanim. 2014 Jun;33(6):411–7.


Joanne Martin

Mob: 021614655