What has hyperbaric treatment to offer?

Treatment with oxygen given under hyperbaric conditions can be life-saving in acute poisoning.
It is generally accepted that if logistically feasible, and if the patient is stable enough to transfer to a unit, those unconscious from CO poisoning should be treated with hyperbaric oxygen (HBOT).
Patients who should be discussed with the nearest hyperbaric chamber facility include those who have been unconscious at any time (irrespective of their current l.o.c.), those with 'hard' neurological findings, pregnant women, and those with pre-existing vascular disease.

HBOT has also been shown to reduce the incidence of DNS and other cognitive sequelae.

Optic and other neuritides

CO is especially toxic to the central and peripheral nervous systems.
Optis neuritis is a recognised sequela of exposure, as is peripheral neuritis (sometimes picking out a single peripheral nerve such as femoral, sciatic, ulnar) and various other patterns of mixed neuronal damage.

Cases in the news

This post will be updated periodically with cases currently in the headlines.

As of November 16th 2006, Crookhill Primary School in Gateshead remains closed following a suspected spillage of CO from three boilers situated under a classroom. The school was initially evacuated on November 14th.

CO - what is it

Carbon Monoxide is just that - the monoxide of carbon. It is therefore combustible; what it really wants to be is carbon dioxide.
It is produced from the partial combustion of any kind of 'fossil' fuel, and also carbohydrate fuels like wood and paper.
It is colourless and odourless (although the Victorian gas experts say it had an odour of garlic about it.) It is about the same density as air, but since it is usually associated with hot combustion gases, tends to rise in an enclosed environment.

Delayed Neuropsychiatric Syndrome (DNS)

Someone poisoned by CO may seem to make a full recovery, only to relapse perhaps several days later with any of a whole gamut of neurological and psychiatric symptoms. These may even be enough to mimic a full-blown organic psychosis.
This link is to a BMJ editorial mentioning this phenomenon.

Stephen Thom has published extensively over many years about the effects of CO, and this article in the Proceedings of the National Academy of Sciences covers DNS in detail. It has 38 references, many accessible on line.

For more coverage of this phenomenon, try this pdf file (you will need Adobe Acrobat Reader) from the World Health Organisation.

How do I protect myself, and those around me?

It's basic, and simple. Be AWARE of the possibility. That means having a basic knowledge of how CO is produced, and how it gets into people.
Be ALERT to the presence of the gas - it practice this means splashing out £30-£40 on a domestic CO alarm - or even two.
Do NOT think that if your gas fire is burning with a nice blue flame, and not leaving any soot marks, that everything is OK. While it is certainly true that poorly-vented gas-burning appliances will produce soot and a yellow flame, by the time this is noticeable, there will be a LOT of CO around.
If you think that you or your family are in a contaminated building, get out, and do not return until you are sure it is safe. You should not use any suspect appliances until they have been inspected by a qualified engineer.

The Roll Call

Here's a short list of CO deaths, culled from the BBC News website.
They happen; they are not rarities, and they can always be prevented, sometimes by timely medical intervention.

The case of Chrisitanne and Robert Shepherd, killed by a water heater at the Corcyra palace Hotel in Corfu.
On Monday October 15th 2007, a memorial garden was opened at Horbury Primary school.


Alex Mitchell aged 14. Florence Holeman and her daughter Marion Stillwell (just around the time of the Corfu tragedy, but got less press coverage.)
Three pensioners die in the same house in Lincolnshire. Inquest verdict on Angela Pinkney, who died in March 2005 despite having called British Gas engineers out 10 times to look at her boiler.
Thomas McCauley and both his great-grandparents died in South Wales in October 2005. Katie Overton, March 2003. Ten year old Dominic Rodgers died in Huddersfield.
The case of Thomas and Doris Sykes, from Wakefield.
Two men died in Malaga in Spain after turning on a faulty gas heater.
Another man dies at a flat in Cleethorpes, in January 2006. That same month, a man and woman die at a house in North Wales. In November 2005 an eldely couple die at a house in Swansea. Back in 2001, David Beak died when poisoned by funes from a petrol heater.
Martin Towey aged 83 and his dog both died in Staffordshire. A rare suicide using CO as the method.
Tom & Hannah Evans, an elderly couple, died in Wales in January 2005. They used solid fuel burner to keep warm. Another Welsh fatality, this time thought to be caused by work that had been carried out on a chimney. In 2004, Keith Turnbull died from CO poisoning while cooking marmalade on a faulty gas stove.
December 2004 - the death of an Oxfordshire man used as a 'warning in new safety campagin.' Again.
March 2003, two students, Michael Frosdick and Ketith Reynolds, die in landlord-rented accomodation. Two men are subsequently convicted of manslaughter.

What are the symptoms?

Symptoms of CO exposure range from minimal disturbances through to fairly speedy death. It depends what concentration of CO you are being exposed to, for how long, how big you are, and also how much you are exercising (it's a gaseous poison - so the more you are breathing, the more quickly you absorb it.)

In adults, the commonest symptom is said to be headache. Also, general malaise, fatigue, muscle aches and pains, and eventually uncontrollable somnolence and unconsciousness.
In children, GI symptoms predominate at low-level exposure. This includes abdominal pain, nause, vomiting and even diarrhoea.

What are 'safe' levels and 'dangerous' levels of CO?

CO concentration is usually expressed in volumetric parts per million ('ppm').
There is no 'safe' amount of CO to be exposed to, if you ask me. That is, given the choice, I would rather not be breathing any at all, thanks all the same!
150 ppm is accepted by some as a 'safe' exposure for a limited period of time. Many domestic alarms will sound their warning at this level.
Others go by the level of 40 ppm, and nothing more than that.

As part of the British Standard EN50292, domestic alarms sold in the UK must not sound an alarm below 70 ppm - presumably to prevent 'false' alarms. Most experts would agree that exposure to this amount of CO for any length of time is very unhealthy indeed.
The only sensible approach is the 'ALARA' principle - 'As Low As Reasonably Achievable.' No amount of CO is good.

The pulse oximtery problem

Although COHb does not make you 'cherry pink' to the naked eye, the absorption spectrum of COHb does cause problems with pulse oximetry.
A simple pulse oximeter simply measures how 'pink' the patient's blood is. "If a patient looks pink to you, they look pink to an oximeter." Pulse oximeters are confused by COHb, and read it as oxy-Hb. So someone with, say, 30, 40 50% COHb on board will have a PulsOx reading ticking along quite happily at 98%!
So not only is simple oximetry useless for detecting CO exposure, it is actually misleading in, for example, someone from a house fire.
The important exception to this are pulse oximeters like the Rad 57, which is designed specifically to test for COHb.

CO doesn't only poison your blood

CO is a potent, multi-system toxin. Although its most famous and immdeiately lethal effect is its affinity for haemoglobin (around 240 times 'stronger' than Hb's affinity for oxygen) it has many other effects too, on many other systems.
It can damage neural tissue directly. It causes rhabdomyolysis. It causes platelet aggregation.
It does loads of other stuff too.
It's produced naturally in the body, at a rate of about 2mls per day, by the enzyme haem oxygenase. Some postulate that haemoglobin itself is actually designed to scavenge physiological CO - hence the otherwise evolutionary inexplicable affinity for Hb with CO in preference to O2.

For a very quick hint at all you never knew about CO, have a look here. More to follow...

CO alarms - they are NOT the same as smoke alarms!

I have met more than one doctor who was under the impression that CO alarms and smoke alarms were one and the same thing. They are not!
A smoke alarm costs around a fiver, and lets you know if there is particulate smoke around. A CO alarm costs around £40 for a decent one. The best have 'real-time' digital displays and will record peak levels.
You can get CO alarms at all major DIY stores, and also through the Tesco website.
There are cheaper ones around that simply change colour in the presence of CO, but would you want to trust one of these if you were asleep or semi-conscious??

How do I test someone?

Bearing in mind the time limitations, testing for CO (or, more accurately, for the presence of COHb) is very useful to 'prove' exposure.
Probably the single most useful tool on the market is the CO-Oximeter. You can see the Rad 57 from Masimo by clicking on this link.
If you are hospital-based, you can also take blood for 'blood gas analysis', making sure your analyser is set to measure for COHb. You do not have to take an aterial sample. COHb is not significantly different in arterial or venous samples, so just take a venous (or capillary) sample in a suitably anticoagulated collector, and measure that.
There are also breath meters like those from Bedfont available. Originally developed to help people give up smoking, but can usefully screen for COHb, especially in the home setting.

CO does NOT bind 'irreversibly' to Hb.

Carboxyhaemoglobin (COHb) is NOT a totally stable compound. It is much less likely to release its CO than oxyhaemoglobin is to release oxygen, but it still does so - it is not an 'irreversible' reaction as some of the books would have you believe.
The half-life of COHb is around 4 hours when breathing 'clean' air (i.e. 21% O2.) This shortens as you breathe a higher concentration of oxygen.
This is especially important to bear in mind if you are faced with testing someone for COHb levels some time after their possible exposure.
If someone comes to see you, say, 12 hours after possible exposure, they will have gone through three half-lives. So they might have had near-fatal levels of 40% COHb at the time, but their measurable levels will now be down to 5% or less.
'Within normal' COHb levels cannot be used to rule out exposure if there is a delayed presentation. As ever, an accurate history is the best tool.

An extractor fan can kill you!

Did you know that in certain parts of the U.S., it is part of the building regulations that every new home is ‘pressure tested’ to make sure it has enough ventilation?
By the way, last time you bought an older house, I bet you had to have en electrical survey. But I bet no-one made you have the gas appliances checked, did they?
In a modern, well-insulated home, if you turn on the bathroom or kitchen extractor fan, the pressure drop created is enough to draw fumes back down a chimney or flue, particularly if that flue or chimney has not ‘warmed up’ yet.

Carbon monoxide does NOT turn you 'cherry pink.'

The red discolouration of mucous membranes caused by the presence of carboxyhaemoglobin is a post-mortem oddity, NOT a clinical sign. You need more than 40% or so COHb to make this colour visible to the human eye, by which time the victim will probably be unconscious.
The absorption spectrum of COHb does affect the way pulse oximeters behave, but it cannot, and must not, be used as a clinical “rule-out” sign for possible exposure.

How do I tell if someone has been poisoned ?

How can I tell if one of my patients has been affected by CO?

Well, it can be difficult. As always, an accurate history is the best starting place. That, and thinking of the possibility in the first place.
For some reason, doctors when faced with more than one person exhibiting similar symptoms thinks 'infection'. Try thinking 'toxic gas' instead, or as well!
Are you looking at more than one member of the household or building occupants with the same or similar symptoms?
Are any PETS in the house behaving oddly too? (Smaller animals, as well as children, are more susceptible than fully-grown adults.)
Do they have any way they could be being exposed to CO? This includes the obvious like gas fires and gas-powered boilers, but also ANY fuel-burning appliance – wood, coal, charcoal, paraffin, oil, etc.
Do they have an adjoining wall or shared chimney with a household that does have any of the above – even if their house does not?
Have they had their gas appliances checked regularly? Have they had their chimneys swept?

One way of 'proving' exposure is to check their COHb level, but you must bear in mind the length of time elapsed between exposure and testing. Read this post for more on this.