Asphyxiant
Definition
A poison that interferes with oxygen delivery or use. Simple asphyxiants (CO2, methane) displace oxygen; chemical asphyxiants (CO, HCN, H2S) block haemoglobin or cytochrome oxidase.
- Simple asphyxiant examples
- CO2, methane, nitrogen, argon
- Chemical asphyxiant examples
- Carbon monoxide, hydrogen cyanide, hydrogen sulfide
- Simple asphyxiant mechanism
- Displaces oxygen from breathing air
- Chemical asphyxiant mechanism
- Blocks haemoglobin oxygen transport or cytochrome oxidase
Common questions
How do toxicologists tell simple and chemical asphyxiation apart at autopsy?+
Simple asphyxiation usually leaves nonspecific findings (petechiae, congestion) and depends on scene data showing an oxygen-poor atmosphere. Chemical asphyxiants leave a chemical signature: carboxyhaemoglobin on CO-oximetry for CO, or cyanide levels in blood, so lab confirmation is what separates the two mechanisms.
Why is cherry-red lividity not reliable for confirming CO poisoning?+
Cherry-red skin and lividity are classic teaching signs of carbon monoxide poisoning but appear inconsistently, fade after death, and can be mimicked by cold exposure or cyanide. Confirmation requires measuring carboxyhaemoglobin saturation in blood, not visual inspection alone.
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