Alcohols, Gases & Cellular Asphyxiants

Ethanol: Acute Intoxication and the Withdrawal Spectrum

Ethanol is the oldest and commonest poison in the emergency department — and the most easily underestimated. On the way in, it slows the brain toward coma; if the drinker is chronic and the bottle is suddenly taken away, the very same brain rebounds into a storm that can kill. Acute intoxication and withdrawal are two ends of one adaptation, and the same molecule sits behind both. The danger is rarely the alcohol you can smell; it is the head injury, the low sugar, or the second drug you assumed away because the patient was "just drunk."

Toxic Alcohols: Methanol, Ethylene Glycol and Fomepizole

Here is the strange truth at the heart of this poisoning: the alcohol the patient swallowed is barely toxic. Methanol from windscreen wash and ethylene glycol from antifreeze do little harm as they are — they mostly make a person look drunk. The catastrophe comes hours later, and it is entirely home-grown. The body's own enzyme, alcohol dehydrogenase, mistakes these alcohols for ethanol and diligently converts them into acids that dissolve the optic nerve and crystallise inside the kidneys. The antidote is therefore not something that neutralises the poison — it is a drug that stops your own liver from manufacturing it. Win the race against that enzyme and the patient walks out unharmed; lose it and they leave blind, or on dialysis, or not at all.

Carbon Monoxide: The Silent Asphyxiant

Most poisons announce themselves — a smell, a taste, a burning throat. Carbon monoxide gives you nothing. It is colourless, odourless, tasteless, and it pours out of the same heaters, stoves and engines that keep us warm and moving. A family goes to sleep with a headache they blame on the flu and some of them do not wake up. What makes it so deadly is not just that you cannot detect it — it is that your monitors can't either. The pulse oximeter glows a reassuring 99%, the blood gas reads a normal oxygen tension, and all the while the tissues are suffocating. Understanding carbon monoxide is a lesson in how a poison can hide in plain sight, in the blood and on the screen.

Cyanide: Choking the Cell's Powerhouse

Most poisons that kill quickly do so by stopping oxygen from reaching the tissues. Cyanide is more sinister: the oxygen arrives, the blood is scarlet, the lungs work perfectly — and the cells still suffocate. It reaches inside the mitochondrion and jams the final enzyme of the respiratory chain, the one machine that lets a cell turn oxygen into energy. Within minutes the body is drowning in lactic acid while its arteries are full of oxygen it cannot touch. This is histotoxic hypoxia — poisoning not of delivery but of use — and understanding it is the key to three very different antidotes.

Methaemoglobinaemia: When Haem Iron Rusts

A patient turns blue, but the oxygen is flowing and the lungs are clear. You crank the oxygen to maximum and the colour doesn't budge; the pulse oximeter sits frozen near 85% no matter what you do; and when blood is drawn it looks not dark red but chocolate-brown. This is not a lung problem or a heart problem. It is a chemistry problem inside the red cell: an oxidising drug has rusted the iron of haemoglobin, and the molecule that carries oxygen has quietly stopped doing its one job. The fix is not more oxygen — it is a dye that runs the chemistry backwards.