Ketamine produces 'dissociative anaesthesia' through its primary receptor mechanism. Which additional receptor interaction MOST accounts for its bronchodilatory effect?
- A Mu-opioid receptor agonism decreasing vagal bronchoconstrictor tone
- B Direct activation of beta-2 adrenoceptors on bronchial smooth muscle
- C GABA-A receptor potentiation causing smooth muscle relaxation
- D Inhibition of neuronal norepinephrine reuptake leading to sympathomimetic bronchodilation ✓
Explanation
Ketamine is a sympathomimetic agent primarily because it inhibits neuronal reuptake of catecholamines (norepinephrine and, to a lesser extent, epinephrine), increasing circulating and synaptic catecholamine levels. These elevated catecholamines activate beta-2 adrenoceptors on bronchial smooth muscle, causing bronchodilation. This indirect sympathomimetic mechanism distinguishes ketamine from direct beta-2 agonists. Ketamine also blocks muscarinic receptors weakly, contributing to bronchodilation and increased secretions. This profile makes ketamine the induction agent of choice in status asthmaticus.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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