E36 Peripheral nerve blocks: awake or asleep?

During recent years, the once widely spread assumption that peripheral nerve blocks (PNB) shell only be performed in awake adult patients has been progressively questioned. The increasing evidences showing the rarity of catastrophic nerve lesions1 and the example of paediatric anaesthesia, where PNB are regularly done under general anaesthesia, with extremely rare complications, have contributed to revive the debate on the opportunity to reconsider this dogma. However, some rational objections could be reasonably presented for consideration by Colleagues sustaining the idea that performing PNB in adult patients is a safe practice, which should become the new standard of care. Catastrophic, permanent nerve injuries after PNB are rare, but they represent only the tip of a very big iceberg, made of a whole range of minor to moderate symptoms related to a nerve suffering. Those symptoms, even if transient, are far more frequent and their incidence after PNB might be as high as 10%.2 Even if characterised by a favourable prognosis, those complications nevertheless often determine a loss of productivity and/or a tangible impairment of patients’ quality of life, consequently representing the main reason for litigations in non–obstetric anaesthesia cases.3 Those litigations outcome does not depend on the entity or duration of the actual damage.4 In case of litigation, the Anaesthetist involved is asked to demonstrate that she has acted lege artis, i.e. doing whatever it takes in order to minimise the portion of controllable risk, beside the intrinsic procedural risk (alea terapeutica). In case she did not, according to the vast majority of European Countries legislations, she can be accused of imprudence in her clinical practice. According to the current level of knowledge, the only way we have to minimize this controllable risk during a PNB is by avoiding nerve puncturing and intraneural injection. Even if it has been shown that paraesthesia might not be elicited in more than a half of awake patients, even in case of needle to nerve contact,5 the concept of compound risk teaches us how even this per se unreliable method can contribute to significantly increase the probability of detecting a nerve puncture, when combined with one or –better– more other methods (ultrasound guidance, nerve stimulation, injection pressure monitoring). Nerve lesions are not the most frequent and potentially catastrophic complications of PNB, nor are the only reason why an awake patients might help to increase the level of safety during these procedures. Local anaesthetic systemic toxicity (LAST) occurs in more than 8% of cases and its incidence is probably increasing, given the increasing popularity of high volume infiltrative blocks.6 In case of accidental intravascular injection, early neurologic symptoms are the only signs, which my guide to the correct diagnosis and induce the Anaesthetist to immediately stop the local anaesthetic injection and initiate appropriate treatment, thus avoiding a potentially fatal progression. This is precisely why current recommendations on acute LAST risk minimisation almost invariably recommend avoiding deep sedation and continuously interacting with patients throughout the procedure. References Barrington MJ, et al. Preliminary results of the Australasian regional anaesthesia collaboration. Reg Anesth Pain Med 2009;34:534-541. Jeng CL, et al. Complications of peripheral nerve blocks. Brit J Anaesth 2010;105:97-107. Szypula K, et al. Litigation related to regional anaesthesia: an analysis of claims against the NHS in England 1995-2007. Anaesthesia 2010;65:443-452. Peng PWH, et al. Litigation in Canada against anesthesiolists practicing regional anesthesia. A review of closed claims. Can J Anesth 2000;47:105-112. Perlas et al. The sensitivity of motor response to nerve stimulation and paresthesia for nerve localization as evaluated by ultrasound. Reg Anesth Pain Med 2006;31:445-450. Linsey EC, et al. Local anaestetic systemic toxicity. Brit J Anaesth Education 2015;15:136-142.

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