Which of the following is NOT a respiratory stimulant?

• A. Soda lime
• B. Carbon dioxide
• C. Ammonium carbonate
• D. Aromatic ammonia spirit

Answer: (A)

Respiratory stimulants are agents that provoke or enhance breathing by irritating airways or by changing blood chemistry to trigger ventilation. Ammonia-based preparations, like ammonium carbonate and aromatic ammonia spirit, release ammonia gas that irritates the nose and airways, producing a reflex breath and increasing respiration. Carbon dioxide itself strongly drives breathing through central and peripheral chemoreceptors, so inhaling CO2 stimulates ventilation. Soda lime, however, is an absorbent used in rebreathing circuits to remove CO2 from the gas mixture; it does not stimulate respiration. Therefore, the option that is NOT a respiratory stimulant is soda lime.