LAST Early Signs — FRCA Final MCQ

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EasyRegional AnaesthesiaLAST Early SignsFRCA Final

A 42-year-old awake man receives an ultrasound-guided femoral nerve block with 20 mL of 0.5% levobupivacaine. Two minutes after the injection, he reports circumoral tingling, tinnitus and a metallic taste. He remains conscious, with an unchanged blood pressure and sinus rhythm, and has no rash, facial swelling or wheeze. Which adverse effect of local anaesthetic is most consistent with this presentation?

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Correct answer: D — Early central nervous system toxicity

Explanation lettering: D = shown as A · E = shown as B · B = shown as C · A = shown as D · C = shown as E

A is correct. Circumoral paraesthesia, tinnitus and metallic taste developing within minutes of injection are prodromal central nervous system manifestations of local anaesthetic systemic toxicity (LAST). The dose given was 0.5% = 5 mg/mL; 20 mL × 5 mg/mL = 100 mg. A dose below the usual maximum does not exclude LAST because inadvertent intravascular injection can produce rapid toxicity, and ultrasound does not eliminate this risk. Cardiovascular toxicity causes hypotension, bradycardia, conduction disturbance or ventricular arrhythmia and generally represents more severe toxicity, although it can occasionally occur without a CNS prodrome. Methaemoglobinaemia produces cyanosis and impaired oxygen saturation rather than this neurological syndrome. Local neurotoxicity causes a focal, often persistent neurological deficit. Immediate hypersensitivity would be suggested by urticaria, angioedema, bronchospasm or hypotension.

Reference: Royal College of Anaesthetists. NAP8: Major complications of regional anaesthesia and other procedures, Local Coordinator Guide v3.3, LAST inclusion criteria. November 2025. https://www.rcoa.ac.uk/sites/default/files/documents/2025-12/FINAL%20NAP8%20LC%20Pack%20v3.3%20%20November%202025.pdf