Which agent is referred to as a 'blood agent' because it prevents the body's ability to use oxygen at the cellular level?

• A. Vesicants
• B. Blood agents
• C. Pulmonary agents
• D. Biological agents

Answer: (B)

Blood agents act by stopping the body's cells from using oxygen. They disrupt cellular respiration in the mitochondria, most famously cyanide compounds that bind to cytochrome oxidase. When this enzyme can’t function, electrons can’t move through the electron transport chain, so tissues can’t extract oxygen even though the blood is delivering it. The result is rapid histotoxic hypoxia, with quick onset of symptoms such as confusion or altered mental status, weakness, and potentially seizures or cardiovascular collapse if exposure continues. In practice, treatment focuses on removing the person from the source, providing 100% oxygen, and using cyanide antidotes when available (for example nitrite-based therapies to form methemoglobin or agents like hydroxocobalamin that bind cyanide).

Contrast that with other agent types: vesicants mainly cause skin and eye blistering; pulmonary agents irritate or damage the lungs; and biological agents are living organisms or toxins with variable, often delayed, effects.