Local Anaesthetic Complication — ORE Part 1 MCQ

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ModeratePharmacology & TherapeuticsLocal Anaesthetic ComplicationORE Part 1

During administration of an inferior alveolar nerve block using a local anaesthetic containing adrenaline, a patient immediately develops sharply demarcated blanching of the ipsilateral cheek and upper lip. What is the most likely cause?

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Correct answer: B — Intra-arterial injection producing vasoconstriction

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

A is correct. Immediate, localised blanching in the cheek and upper-lip distribution following an inferior alveolar block is a recognised consequence of inadvertent arterial injection of an adrenaline-containing solution. Arterial spread and adrenaline-mediated vasoconstriction/vasospasm transiently reduce cutaneous perfusion. The UK SmPC for lidocaine with adrenaline specifically warns to avoid intravascular injection and advises aspiration before and during injection. Allergy is more likely to cause urticaria, angioedema, wheeze or hypotension rather than sharply demarcated pallor. Facial nerve involvement causes ipsilateral weakness, not skin blanching. Infraorbital nerve injury would cause altered sensation, and air embolism would cause serious cardiorespiratory or neurological features rather than isolated facial pallor.

Reference: electronic Medicines Compendium. Lidocaine 2% with adrenaline (epinephrine) 1:200,000 solution for injection: Summary of Product Characteristics, sections 4.2, 4.8 and 5.2. Current UK SmPC. https://www.medicines.org.uk/emc/product/2396/smpc