Carbon monoxide poisoning

Carbon monoxide forms wherever fuel burns without enough air: in a faulty water heater, in a stove whose damper was shut too early, in a barbecue carried indoors, in an engine left running in a garage. It does not sting the eyes and does not make you cough, so nobody backs away from it the way people back away from smoke. That is exactly the trouble: the poisoning builds up quietly, often during sleep, and its signs are put down to a cold, to tiredness or to bad food until the very last moment.

Why you cannot sense it

The gas is colourless, has no smell and does not irritate the airways: none of the senses responds to it. Once in the lungs it binds to haemoglobin hundreds of times more readily than oxygen and barely lets go. Blood keeps flowing, but it can no longer carry oxygen, and the first organs to suffer are the ones that use oxygen fastest, the brain and the heart. The gas also gets in the way of muscle cells, which is why weakness comes before breathlessness.

Two things mislead even medical staff. The famous cherry-red skin colour is uncommon and mostly seen in severe poisoning, so a normal complexion rules nothing out. And a home pulse oximeter shows normal readings: it cannot tell haemoglobin bound to the gas from haemoglobin carrying oxygen, so it reassures at the very moment when reassurance is wrong.

Where it comes from at home

The source is always the same: combustion without enough incoming air, or without a proper way out for the fumes.

• gas water heaters and boilers, especially old ones, moved without professional help or unserviced for years;
• wood and coal stoves, fireplaces and boilers with a blocked or iced-up flue, or with the damper closed too soon;
• gas cookers used to heat a room, and paraffin or gas heaters with no outlet to the outside;
• a barbecue, grill, charcoal briquettes or a camping stove brought into a flat, garage, tent or car;
• a generator, a car or a cultivator left running in a garage, even with the door open;
• smoke from a fire, which accounts for a large share of severe poisonings;
• a water pipe or shisha: the charcoal gives off carbon monoxide and it is usually smoked indoors.

There is also a rare cause that almost nobody knows about. Paint strippers, degreasers and some adhesives contain dichloromethane. It is not carbon monoxide itself, but the liver turns it into carbon monoxide inside the body. That is why, after working in an unventilated workshop, someone feels worse not straight away but several hours later, and keeps getting worse even though they have long been outside. If the illness followed work with solvents, say so to the doctor plainly.

Indirect clues are worth knowing too: a yellow or orange flame instead of a steady blue one, soot around a burner or a stove door, windows misting up in the room where the appliance runs, a flame that keeps going out for no reason.

What it feels like

The first sensations give nothing away: a dull headache across the forehead and temples, nausea, dizziness, sluggishness. Then come vomiting, ringing in the ears, breathlessness on ordinary effort, a pounding heart and a heavy chest. In heavier poisoning coordination goes, the person fumbles over simple things and becomes drowsy or, on the contrary, restless for no reason.

More reliable than the symptoms themselves is their pattern: three clues are worth ten descriptions.

• several people in the same home feel ill at once, sometimes the pets as well, since birds and cats react before humans do;
• an hour or two outdoors brings clear relief, and everything starts again after going back inside;
• the illness began with the heating season, with lighting the stove, with switching on the water heater, or with an engine running nearby.

There is no runny nose, no sore throat and no fever, yet it gets blamed on flu precisely because the head aches and the stomach turns.

When there is no time to lose

Call the emergency number (112 across Europe) at once and get everyone out into fresh air if anyone has:

• loss of consciousness, even briefly, or cannot be woken;
• confusion, muddled speech, odd behaviour, seizures;
• difficulty breathing or blue lips;
• chest pain, or a fast and irregular heartbeat;
• an unsteady gait, or an inability to stand and walk.

Help is called without hesitation for anyone pregnant, whatever the apparent severity, and for small children, older people and anyone with heart or lung disease or anaemia. In an unborn baby the gas clears from the blood more slowly than in the mother, so moderate poisoning in pregnancy is treated as severe. Do not drive: the gas blunts attention and reaction time, and consciousness can fail on the way.

What to do in the first minutes

• Go outside and take everyone with you, pets included. Outdoor air matters more than anything you can do indoors.
• On your way out open windows and doors and switch the appliance off, but do not linger over it and do not go back in for it.
• Do not light a flame and do not smoke until you are sure there is no leak of fuel gas.
• Call for help and stay outside: feeling better in the open air is not recovery, the gas takes hours to clear.
• Do not return indoors until an engineer has checked the appliance.
• Tell the doctor who else was there. Everyone who breathed the same air needs assessing, including those who feel fine.

How doctors treat it

The mainstay is oxygen, started as early as possible, before any test results. Left alone, the gas leaves the blood slowly: on ordinary air it takes hours, and on pure oxygen through a tight-fitting mask considerably less. That is why oxygen is kept up for a long time, even once the person feels reasonably well.

The share of haemoglobin bound to the gas is measured in a blood sample in the laboratory, not with a pulse oximeter. An electrocardiogram and heart blood tests are usually added, because the heart muscle is often affected quietly. If the symptoms are marked, brain imaging is arranged as well.

In severe cases — loss of consciousness, neurological signs, pregnancy, a high level of the gas in the blood, evidence of heart damage — treatment with oxygen at raised pressure in a hyperbaric chamber is considered. Such chambers are not available everywhere, and the decision rests with the doctor, weighing the person's condition and the time since exposure.

The mark it leaves afterwards

People are rarely warned about this, and it is worth knowing. In some, days or weeks after an apparent recovery, delayed problems appear: gaps in memory, trouble concentrating, slowness, a changed character, irritability, sometimes stiff movements and an unsteady walk. It follows severe poisoning with loss of consciousness most often, but it happens after moderate poisoning too.

Most people recover, though it takes months. For that reason it is sensible to be seen again two to four weeks later, even if you were sent home in good shape, and sooner if those around you notice the person has become someone else. The heart is checked as well: rhythm disturbances and reduced tolerance of exercise can surface later.

What actually protects you

• A carbon monoxide alarm in every room with a gas, wood, coal or oil-burning appliance, and without fail near the bedroom.
• A smoke alarm does not detect carbon monoxide: these are different devices.
• Testing the alarm with its button once a month, changing the battery as instructed, and watching the unit's own expiry date.
• An annual check of the boiler, water heater and stove by a qualified engineer, and before the cold season a sweep of flues and vents with a draught test.
• Never sealing ventilation grilles completely: airtight windows plus blocked vents starve the burner of air.
• Never bringing a barbecue, grill or camping stove into a house, garage, tent or car, never heating a room with a gas cooker, and never leaving an engine running in a garage.
• After high winds, heavy snow or roof work, checking the chimney top: snow, leaves and birds' nests block it.

If the alarm sounds, treat it as a real warning rather than a fault: go outside and call an engineer.

Online consultation

In an online consultation the doctor goes through the circumstances in which the illness appeared and whether it coincided with a stove, a water heater or a running engine, judges who else in the household should be checked, explains which tests make sense after an acute episode and which late signs to watch for. If poisoning is suspected right now, the first steps are to get outside and call the emergency services, not to wait for a reply in a chat window.

This material is for information only and does not replace medical advice.