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Systemic Asphyxiant Chemical-Warfare Agents

(Systemic Asphyxiants)


James M. Madsen

, MD, MPH, U.S. Army Medical Research Institute of Chemical Defense (USAMRICD)

Last full review/revision May 2019| Content last modified May 2019
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There are many types of chemical-warfare agents that affect different parts of the body. Systemic asphyxiants poison cells throughout the body and include

  • Cyanide compounds

  • Hydrogen sulfide

Systemic asphyxiants have also been called blood agents because they are distributed through the blood. However, they damage cells throughout the body, not just blood cells.

Cyanide compounds include hydrogen cyanide and cyanogen chloride, which are highly volatile liquids or gases at room temperature. The combustion of many household and industrial chemicals can produce cyanides, and people suffering from smoke inhalation from any kind of industrial or household fire may also have cyanide poisoning. Although cyanide has a characteristic odor of bitter almonds, about half of people lack the ability to detect it.

Did You Know...

  • The combustion of many household and industrial chemicals can produce cyanide.

Hydrogen sulfide is always a gas at room temperature, so exposure to it is usually by inhalation. Hydrogen sulfide can be produced by mixing sulfur-containing household chemicals with acids. Residual gas can affect rescuers, causing many additional casualties. Hydrogen sulfide is also produced when manure decomposes. Large farm manure pits often contain lethal quantities of the gas. Hydrogen sulfide has a characteristic rotten egg odor, but high concentrations damage a person's ability to detect the odor.


Cyanide initially causes gasping, a rapid heart rate, and high blood pressure. People may have seizures and lose consciousness in as little as 30 seconds. They may display signs that are similar to those of tetanus, including lockjaw, grimacing, and arching of the neck. Their skin may appear flushed, but about half of people have a blue tinge to their skin.

Hydrogen sulfide at high doses also can cause people to have seizures and lose consciousness. They may sustain heart damage. Continued exposure to low doses of hydrogen sulfide may irritate the eyes and membranes lining the nose and throat and cause headache, weakness, incoordination, nausea, vomiting, chest tightness, and hyperventilation.


  • A doctor's evaluation

Severely affected people must be treated immediately, so doctors base the diagnosis on the person's symptoms and history. After exposure to hydrogen sulfide, any coins that the person is carrying may have a green discoloration or darkening, which could increase the doctor's suspicion of hydrogen-sulfide exposure. Commonly ordered blood tests may suggest exposure to hydrogen cyanide or hydrogen sulfide, but only specialized tests can confirm it.


  • Ensuring person can breathe

  • Decontamination of skin

  • Antidotes if available

  • 100% oxygen

Doctors give immediate attention to the person's airway, breathing, and circulation. Skin can be decontaminated using water with or without soap.

Cyanide antidotes are available and include amyl nitrite, sodium nitrite, sodium thiosulfate, and hydroxocobalamin. If the antidotes are not available, doctors give the person 100% oxygen. Unprotected mouth-to-mouth resuscitation may expose the rescuer to cyanide in the person's breath.

People exposed to hydrogen sulfide are usually given 100% oxygen. Glucose and bicarbonate given by vein (IV) may be helpful.

The views expressed in this article are those of the author and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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