Carbon monoxide poisoning signs: symptoms, what to do and treatment

Carbon monoxide is a poisonous gas you cannot see or smell. Poisoning often starts with symptoms that feel like flu or a bad day, which is why it is easy to miss. If you think you or someone you live with has been exposed, the priority is simple: get outside and get medical help. HBOT Medics is not an emergency service. Anyone with suspected carbon monoxide poisoning needs NHS emergency care.

What are the signs of carbon monoxide poisoning?

The NHS lists these symptoms of carbon monoxide poisoning:

• a headache
• dizziness
• feeling sick or being sick
• feeling weak
• tiredness and confusion
• chest and muscle pain
• shortness of breath
• your face turning hot and red (flushing), which can be harder to see on brown and black skin
• loss of vision

The symptoms may come and go. The most useful clue is the pattern. The NHS says they may get worse when you spend time in an affected room or building and get better when you leave or go outside.

Early signs are easy to put down to something else. The Health and Safety Executive notes that they can mimic common ailments and be confused with food poisoning, viral infections, flu or simple tiredness. UK government guidance on carbon monoxide adds that long exposure to small amounts can cause flu-like symptoms, with tiredness, headaches, nausea, dizziness, personality changes and memory problems.

Who is most at risk?

The NHS England commissioning policy on carbon monoxide poisoning says children, pregnant women and older people are more at risk of harm. So are people with conditions that affect oxygen delivery to the heart or brain, such as coronary heart disease, angina, asthma or anaemia.

What should you do if you suspect carbon monoxide poisoning?

The NHS advice is:

1. Stop using appliances you think might be making carbon monoxide, such as a boiler, cooker or heater, if you can.
2. Go outside.
3. Get medical advice as soon as possible, and do not go back into the building until you have.

Call NHS 111 if you think you might have symptoms of carbon monoxide poisoning.

Call 999 or go to A&E if you think you or someone else has been exposed and they:

• are finding it hard to breathe
• have suddenly become confused
• have lost consciousness
• are feeling weak
• have chest or muscle pain

Do not drive yourself to A&E. The NHS says to ask someone to drive you, or to call 999 and ask for an ambulance.

If you think a gas appliance is leaking carbon monoxide, the NHS says to call the free National Gas Helpline immediately on 0800 111 999. It is open 24 hours a day. Do not use the appliance again until it has been checked by a qualified, registered engineer.

Where does carbon monoxide come from?

Household appliances used for heating and cooking can produce carbon monoxide if they are not installed properly, are faulty or are poorly maintained. The NHS names gas boilers, gas cookers and clay ovens, gas or paraffin heaters, wood, gas and coal fires, and portable generators. Using a barbecue or camping stove indoors, or running a vehicle or lawn mower engine in an enclosed space such as a garage, can also cause a dangerous build-up.

It is not rare. The NHS England policy reports 102 deaths from accidental carbon monoxide poisoning in England and Wales across 2015 and 2016, and estimates that around 4,000 people are diagnosed with carbon monoxide poisoning at A&E each year.

How is carbon monoxide poisoning treated?

Carbon monoxide binds to haemoglobin, the oxygen-carrying part of red blood cells, about 210 times more strongly than oxygen does, according to the NHS England policy. The blood then carries far less oxygen to the brain and heart, which are the organs most sensitive to a shortage.

In hospital you will usually have tests to check the level of carbon monoxide in your blood, and you may be given oxygen through a mask. The NHS England policy describes standard treatment as removal from the source, 100% oxygen through a tight-fitting mask, and general supportive care. Breathing ordinary air, it can take around 320 minutes for the level of carbon monoxide bound in the blood to halve. Pure oxygen at normal pressure shortens that about five-fold. Follow-up is arranged for people with lingering symptoms.

A home finger pulse oximeter is not a reliable check. The StatPearls review of carbon monoxide toxicity explains that standard pulse oximeters cannot tell carbon monoxide bound to blood apart from oxygen, so a normal reading does not rule poisoning out.

Some problems can appear later. NHS England describes delayed neurological sequelae: new symptoms that appear or return days to weeks after poisoning. They range from subtle personality changes, mood problems and memory loss to, much less commonly, more serious brain injury. The policy notes that up to a third of survivors of severe poisoning are thought to be affected. If you notice new problems with memory, mood or concentration in the weeks afterwards, tell your GP.

Is hyperbaric oxygen therapy used for carbon monoxide poisoning?

Sometimes, in specialist centres, and the evidence is genuinely mixed.

The reasoning is straightforward. Breathing oxygen under pressure clears carbon monoxide from the blood faster: NHS England notes that hyperbaric oxygen at 3 ATA shortens its half-life to 15 to 30 minutes. It may also dampen the inflammation that severe poisoning is thought to trigger. The Undersea and Hyperbaric Medical Society lists carbon monoxide poisoning among its accepted indications for hyperbaric oxygen.

The trials are less clear:

• A 2002 double-blind trial in the New England Journal of Medicine randomised 152 people with symptomatic acute poisoning to three chamber sessions within 24 hours. According to the Cochrane review's description, the hyperbaric group's first session was 1 hour at 3 ATA and 1 hour at 2 ATA, followed by two 2 hour sessions at 2 ATA. Cognitive problems at 6 weeks affected 25.0% of the hyperbaric group and 46.1% of the normal-pressure oxygen group. The trial was stopped early after an interim analysis.
• A Cochrane review from 2011 analysed six randomised trials with 1,361 participants. Two found a benefit at one month and four did not, and the pooled result was not statistically significant. The authors found design or analysis flaws in all the trials and noted that both positive trials were stopped early for benefit, which is likely to have inflated the effect. They concluded that existing trials do not establish whether hyperbaric oxygen reduces lasting neurological problems.

NHS England reviewed the 2002 trial alongside a smaller 1995 trial of 65 people treated at 2.8 ATA and then 2.0 ATA. It found some benefit, but both studies had significant methodological limitations, and some effects did not last. Its policy, in force since April 2019, is that NHS England will not routinely commission hyperbaric oxygen therapy for carbon monoxide poisoning, pending at least one further good-quality trial. Where it has been used in the UK, patients were treated in the acute phase, most often within 24 hours.

Can a private HBOT clinic help after carbon monoxide poisoning?

No. HBOT Medics is not an emergency service, and this is not a condition we treat.

Our single-person soft-shell chamber runs at 1.5 ATA for planned, screened sessions. The carbon monoxide trials above used 2.0 to 3.0 ATA and treated people in the acute phase, soon after exposure. If you suspect carbon monoxide poisoning, do not travel to us or to any private or wellness chamber. Go outside, and call 111, 999 or go to A&E as described above. If you have lingering symptoms afterwards, your GP is the right first contact.

If you want to understand how hyperbaric oxygen works outside emergencies, our pages on what HBOT is and what hyperbaric oxygen therapy is explain the mechanism and where the evidence is established. Our chamber page sets out the pressure we use and how it compares with research.

How can you prevent carbon monoxide poisoning?

UK government guidance recommends:

• having cooking and heating appliances that burn gas, oil or coal serviced regularly by a qualified, registered engineer: Gas Safe Register for gas, HETAS for solid fuel and OFTEC for oil
• keeping rooms properly ventilated, with chimneys and flues swept from top to bottom at least once a year and never blocked
• fitting an audible carbon monoxide alarm that meets British or European standards (BS Kitemark or EN 50291)

The NHS suggests getting an alarm that makes a loud sound for each room of your home containing appliances that burn gas, oil, coal or wood. An alarm protects you from high levels, but government guidance warns that it will not go off at lower levels, so it is not a substitute for servicing. The NHS adds some everyday rules: do not use barbecues or camping stoves indoors, do not run vehicle or lawn mower engines in an enclosed space, and do not use oversized pots that cover more than one gas ring.

The short version

A headache, dizziness, sickness or breathlessness that eases when you leave home can be carbon monoxide. Stop using the appliance if you can, go outside and get medical advice. Call 999 or go to A&E for breathing difficulty, sudden confusion, weakness, chest pain or collapse. Fit an alarm, have appliances serviced, and remember that emergency treatment happens in hospital.