During desflurane delivery at a vaporiser setting of 6%, the anaesthetist notes tachycardia and hypertension 5 minutes into induction. Which physiological mechanism is responsible?

• A Direct myocardial stimulation via L-type calcium channels
• B Inhibition of baroreceptor-mediated vagal tone
• C Peripheral vasodilation causing reflex tachycardia
• D Sympathoadrenal activation triggered by airway irritation and rapid concentration increase ✓

Explanation

Rapid increases in desflurane concentration (especially above 1 MAC) cause transient sympathetic activation manifesting as tachycardia and hypertension. This is attributed to airway irritation (desflurane's pungency triggers upper airway reflexes) and direct sympathoadrenal stimulation. Unlike isoflurane or sevoflurane, desflurane is unsuitable for inhalational induction. The response is blunted by pre-treatment with fentanyl, beta-blockers, or clonidine.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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