Cyanide suffocates cells even while the blood stays full of oxygen
Cyanide does not stop you breathing air; it stops your cells using it. By jamming a key enzyme in the mitochondria, it leaves oxygen stranded in the blood, which is why victims can look flushed rather than blue. Its most common modern source is ordinary: smoke from burning buildings.
The target is cytochrome c oxidase, the last step of the chain that lets cells turn oxygen into energy. Cyanide latches onto its iron-copper centre, so electrons can no longer reach oxygen, and energy production grinds to a halt. Doctors call this histotoxic hypoxia: tissues starve despite a normal oxygen supply. Venous blood stays unusually oxygenated, sometimes giving skin a cherry-red tint, and despite the shared root, cyanide does not directly cause cyanosis. Plants cope better because they have a bypass route that skips the blocked enzyme.
Exposure comes in many forms. Hydrogen cyanide gas and salts such as potassium cyanide are the classic poisons, but burning polyurethane, vinyl and similar plastics releases the gas in fires. Traces occur in apple and apricot seeds, bamboo shoots and cassava; badly processed cassava eaten over long periods has been linked to paralysis and thyroid problems. Metal polishing, some insecticides and the blood-pressure drug sodium nitroprusside are other routes. Symptoms usually start within minutes, beginning with headache, dizziness and a racing heart and progressing to seizures and collapse.
Diagnosis is tricky because blood tests take time. Clinicians look for clues such as a high lactate level after smoke inhalation, since cells forced into anaerobic metabolism pile up lactate, though other conditions do the same. Treatment centres on removing the person from the source, pure oxygen and an antidote. Hydroxocobalamin, a form of vitamin B12 approved in the US in late 2006, is generally first choice. Older nitrite antidotes work by creating a decoy form of haemoglobin that soaks up cyanide. Ireland's health service stopped recommending any single antidote after raising doubts about several.
Fires show the danger vividly. At the Kiss nightclub in Santa Maria, Brazil, in January 2013, burning soundproofing foam released cyanide, and 242 deaths were confirmed by March, the deadliest fire involving cyanide poisoning. The gas also has a darker history: Nazi Germany used the hydrogen cyanide product Zyklon B from 1942 to murder roughly one million people, most of them Jews, in extermination camps such as Auschwitz-Birkenau.
Source: Cyanide poisoning
