Carbon monoxide info for doctors

Android phone app

2011-11-17T14:47:00.001Z

I've been working for a year now with our friends at univirtua.com on a free Android phone app warning of the dangers of carbon monoxide.
It will be launched on Monday 21 November. When further details are available, I will post again about how to access the app.

CO Awareness week 2011

2011-11-17T14:45:00.001Z

Our annual awareness week starts on Monday 21 November at the House of Lords.
Full week's agenda at www.covictim.org.

LinkedIn updates

2011-10-27T09:47:00.002+01:00

Apologies to anyone who accesses this blog to find a posting from LinkedIn taking over the page. Once I figure out how to disable this and stop LinkedIn automatically accessing my blog and altering it, I will do just that !
In the meantime I'll just have to delete the messages as they appear...

Carbon monoxide - an old enemy forgot. Thirty years on...

2011-10-11T09:31:00.002+01:00

This article (download HERE) is from The Lancet of 1981. Much of it could have been written yesterday...

Journal of Physiology updated!

2011-06-18T09:32:00.003+01:00

116 years after JS Haldane published his seminal work on carbon monoxide, the Journal of Physiology publishes a paper outlining CO as an emerging regulator of ion channels.

The original Haldane paper is available here.

The latest publication is available here.

Carbon monoxide fumes killed elderly couple while they watched television

2011-05-13T19:50:00.002+01:00

Click here for this story

Health group launches at House of Lords

2011-05-06T11:44:00.002+01:00

Carbon Monoxide - protect your patients; protect yourself.

A unique group is being formed by Lynn Griffiths of the charity Carbon Monoxide Awareness. The aim of the group is to ensure that best practice is followed by all professionals who might be the first contact point of carbon monoxide victims with health services. This includes ensuring that emergency responders are not exposed to danger themselves.

Unfortunately, and sometimes tragically, improper advice based on outdated beliefs is frequently given to those exposed to carbon monoxide. False reassurances based on poorly interpreted investigations are commonplace. Often the diagnosis is not even considered, although a patient presents with classic signs and symptoms. Never was the phrase 'prevention is better than cure' more appropriate than for CO poisoning.

To take this forward we are having a brief inaugural meeting of the group on Tuesday June 14th at 1pm. The meeting will take place in Committee Room 1 at the House Of Lords. We already have representatives from the colleges of emergency medicine and general practitioners attending, as well as paramedics and pharmacists. Any other interested parties are warmly invited to attend.

Gas Safety Trust report

2011-04-18T11:16:00.002+01:00

Congratulations to all involved in the 'Hotspot' report from the Gas Safety Trust. You can get a copy of the report by clicking here - Posted using BlogPress from my iPad

Delayed neuropsychological sequelae after carbon monoxide poisoning: predictive risk factors in the Emergency Department. A retrospective study

2011-03-18T09:40:00.002Z

Click on this link for the paper

- Posted using BlogPress from my iPad

CORM

2011-03-13T09:17:00.001Z

Evidence mounts that CO does far, FAR more than simply bind to haemoglobin (sorry Professor Haldane). For the very latest, try an on-line search for "CO releasing molecules". A very experimental form of pharmaceutical preparation with possible therapeutic effects.

- Posted using BlogPress from my iPad

Ambient air pollution and congenital heart disease

2011-03-07T21:06:00.001Z

Newcastle-based researchers show a link between some kinds of congenital heart disease and low-level CO exposure.

Click here for the paper

- Posted using BlogPress from my iPad

Factors affecting the prognosis of patients with delayed encephalopathy after acute carbon monoxide poisoning

2011-02-25T08:43:00.004Z

Hyperbaric oxygen therapy (HBOT) remains controversial. But there is increasing evidence that its use early in more severe cases of poisoning can reduce the incidence of long-term problems, in particular the delayed neuropsychiatric syndrome.

http://bit.ly/e8Zqmb

- Posted using BlogPress from my iPad

Carbon Monoxide Awareness week 2010

2011-02-24T13:48:00.001Z

New World Health Organisation guidelines

2011-01-12T11:50:00.002Z

The WHO have just released their new guidelines for indoor air quality.
The new recommendation is a maximum permitted level of around SIX parts per million of CO averaged over a 24 hour period. This reflects the evolution of the way in which we understand CO toxicity.
You can obtain a copy of the report by following this link. Information about CO (co-authored by Dr David Penney) starts at around page 55.

Major pub chain sentenced over Merseyside landlord's death

2010-12-16T20:11:00.002Z

This press release from the HSE makes tells a terrifying but all too familiar story.

Chronic low level exposure and cognitive impairment

2010-12-12T14:22:00.002Z

Low level exposure to CO shown to cause cognitive impairment in student volunteers.

CO makes you dizzy..

2010-12-12T13:48:00.002Z

An 'unusual' case of dizziness reported in the Journal of Laryngology and Otology.

Amanda's Law

2010-12-12T13:36:00.002Z

It is now mandatory for domestic dwellings in the state of New York to be fitted with CO alarms. More information here.
How long before we get similar legislation in the UK?

On-line teaching module now available

2008-05-16T10:02:00.002+01:00

I am very happy to say that an on-line teaching module on CO poisoning is now available on the doctors.net.uk website. You need a GMC number to register on this site, but I'm hoping to make this module available on the medical student section of the site too.
When you log in, go to 'Education', then 'College of Emergency Medicine' (in the bar on the left) and the 'Carbon Monoxide Poisoning' module is listed there.

Delayed neurological symptoms are immune-mediated

2008-04-08T12:08:00.002+01:00

This paper by Stephen Thom in the Proceedings of the National Academy of Sciences of the USA postulates an immune-mediated mechanism for the phenomenon of delayed neuropsychiatric sequelae following non-fatal CO exposure.

DNS is not a new phenomenon

2008-03-28T11:57:00.002Z

The delayed neuropsychiatric syndrome associated with CO exposure is in no way a newly-discovered phenomenon, as this paper from JAMA of 1912 illustrates.

EMJ supplement

2008-03-28T11:49:00.001Z

I published an article in the EMJ (Emergency Medicine Journal) supplement of November 2007. You can download a copy for free by clicking here.

CO and cardio-toxicity

2008-03-25T09:21:00.002Z

Reuters news agency have a story based on a paper in the journal Academic Emergency Medicine which looks at the cardio-toxicity of CO in rats.
Also mentioned is an earlier paper in the Journal of the American Medical Association which examines long term morbidity and mortality in those exposed non-lethally to carbon monoxide. You can get a free pdf file of this paper from the JAMA website by clicking here.

On-line module from the CEM

2008-03-12T11:18:00.001Z

I have written an on-line teaching module on the presentation and treatment of carbon monoxide poisoning. This is under the auspices of the College of Emergency Medicine, and should be available through the doctors.net.uk website in the very near future - hopefully before the end of April.

Parliamentary news

2008-03-12T11:15:00.003Z

The All Party Parliamentary Gas Safety Group meets at the House of Commons on April 23rd. I have been invited to inform them of efforts being made to ensure the highest possible level of awareness and education is being achieved and maintained among the medical community.

Another fatality...

2008-02-28T09:39:00.003Z

Another probable CO-related death, in London, as reported this morning on the BBC News website.
The BBC call it a 'carbon monoxide leak', which is unusual terminology.

Historical aspects

2007-10-23T17:34:00.000+01:00

One of my particular interests is in the history of carbon monoxide poisoning. I have quite a collection of old (some very old) medical research - a lot of it still very relevant to today.
I am planning to make a lot of this accessible through this site. To start with, clicking on this link will allow you to download a copy of a publication from 1970, in the Postgraduate Medical Journal. Medics from Newcastle describe their experiences of carbon monoxide over a three-year period. This was during a period when coal gas was piped into people's homes. The figures they cite are pretty amazing!

CO-Awareness Week 2007

2007-10-16T14:20:00.002+01:00

As medical advisor to CO-Awareness, I am very pleased to be associated with the launch of the CO-Awareness week.
The week began with a seminar at the House of Lords on Monday October 15th. The meeting was chaired by Barry Sheerman MP, along with Lord McKenzie from the Department for Work and Pensions.
On Friday October 19th the CO-Awareness roadshow hits Dewsbury in West Yorkshire. From 10am we will be at Dewsbury Town Hall with information and discussion around carbon monoxide.
Details on the venue can be found by clicking here.
According to the recent CORGI Report, people in the Yorkshire region are at greatest risk from accidental CO exposure in the home.

Thinking of getting a CO alarm?

2007-10-16T14:20:00.001+01:00

Well, that means you haven't already got one, which is NOT good, but at least you're going to get one.
Get one today.
Get one that sounds an audible alarm, and that has the British Standard ('Kitemark') EN50291.
Better still, get one that has a digital display/readout, and also records peak levels.
One per household is an absolute minimum - one per flame-producing appliance (so one for every fire, boiler, cooker etc. in the house) is the ideal.
Consult the instructions that come with your alarm for the best place to fit it.

Independent article

2007-10-02T13:48:00.000+01:00

There is an interesting insight into the aftermath of carbon monoxide poisoning written by Richard Gill in the Independent of September 25th.
The piece also highlights that charcoal burning is a potent source of CO.

New trial on HBOT (hyperbaric oxygen therapy)

2007-09-28T15:01:00.000+01:00

Lindell Weaver and colleagues at Salt Lake City have just published their latest research on HBOT, in the America Journal of Respiratoy and Critical Care Medicine.

You can get a pdf copy of the paper by clicking this link:

Carbon monoxide Poisoning: risk factors for cognitive sequelae and the role of hyperbaric oxygen.

CO Awareness week

2007-09-22T10:17:00.001+01:00

CO Awareness week kicks off with an event at the House of Lords on Monday October 15th, starting 10.30am.
Then on Tuesday 16th, there's a meeting at the HSENI (Health & Safety Execuive of Northern Ireland). Wednesday the venue is the Welsh Assembly; Thursday it is the Scottish Parliament, and Friday October 19th the final event is at Dewsbury Town Hall, 10am start.
Directions at http://www.kirklees.gov.uk/events/venuedetails.asp?vID=22

On-line teaching module

2007-09-22T10:17:00.000+01:00

I have submitted an on-line teaching module on carbon monoxide, aimed mainly at emergency physicians (of all grades.)
This will hopefully be available in October 2007 via the College of Emergency medicine website, and www.doctors.net.uk.
More details and relevant links to follow soon.

Delayed Neuro problems - a Korean case

2007-07-10T16:42:00.001+01:00

An interesting recent case report from Korea illustrating a case of delayed neuropsychiatric sequelae.
South Korea has one of the highest incidences of domestic, unintentional CO poisoning in the world, with a death rate about ten times that in the UK. This is thought to be thanks to the traditional heating methods in some Korean homes, which is to leave a large lump of charcoal smouldering underneath the house overnight.

CORGI report

2007-07-10T16:37:00.001+01:00

Hot off the press (or the pdf converter, anyway) is the latest report from CORGI into CO poisoning.
You can download a copy by clicking here.

How does CO poison...?

2007-07-10T16:33:00.000+01:00

Confused about the toxicology of CO poisoning?
Try this excellent overview from Toxicology in 2003.

CO Awareness Capmaign Leaflets

2007-04-11T20:28:00.000+01:00

You can download a copy of the latest advice leaflet from CO Awareness by going to the 'Useful Documents' box at the very bottom of this page.

An unusual side-effect of CO.

2007-04-08T17:30:00.000+01:00

This recent post on prnewswire.com lists an unusual consumer danger from CO. It is apparently sometimes used to make packaged meat appear 'fresher' (i.e. pinker) than it really is!

You can see a warning video animation about this here.

'Delayed postanoxic encepalopathy'

2007-04-07T16:57:00.000+01:00

Another name for 'DNS', or Delayed Neuropsychiatric Sequelae.
A case report from the Emergency Medicine Journal (http://emj.bmj.com/cgi/content/full/21/2/250).

pdf copy available by clicking here.

CO messes with your head - it's official.

2007-04-07T16:45:00.000+01:00

It's quite well known that students are at high risk of CO exposure. What is less well known is that they are sometimes put deliberately at risk by their professors!
This valuable piece of research (Archives of Neurology 1998; 55 (6), 845) shows just how damaging low-level CO exposure is to the CNS. But I'm not sure it should have received ethical approval!

By going to this link to my public folder on box.net you can retrieve a pdf copy of this paper.

Forgotten anything lately... ?

2007-04-07T16:40:00.000+01:00

Many people exposed to CO over long periods report problems with short-term memory as a consequence.
Could this paper have any connection with this phenomenon ?

Inexpensive CO alarms

2007-03-13T14:44:00.001Z

Calendar, the Yorkshire regional ITV news programme, has a campaign currently running around CO safety.
On this page there are details of local manufacturers and distributors of inexpensive domestic CO alarms and detectors.

CO Awareness Meeting at House of Lords

2007-03-13T14:44:00.000Z

Lynn Griffiths of CO Awareness organised a meeting at the House of Lords on March 7th. This was a very useful starting point for discussion around current issues.
Dr. Ben Croxford presented the results of his survey into CO in domestic environments. You can see those results by clicking here, or by downloading the pdf file directly from the 'Useful Documents' box at the very bottom of this page.

One lady at the meeting was poisoned for 18 months longer than she need have been, all because a doctor in A&E told her that oil-fired appliances could not be a source of CO !

The main thrust of the meeting was discussion of the dangers of chronic, low-level exposure to CO. The gas is a potent toxin, and appears to favour the central and peripherous nervous systems when the victim is exposed to low levels over a period of time. More research in this area is certainly warranted.

The government pamphlet Indoor Air Pollution - Carbon Monoxide ends with the line 'Ask your doctor for advice if you feel ill'. Would you know what advice to give?

The Time Problem...

2006-12-11T11:29:00.000Z

As mentioned elsewhere in this blog, COHb (carboxyhaemoglobin) is NOT a stable compound. It has a half-life of around four hours when you breathe 'clean air (i.e. 21% O2), which shortens the higher the concentration of oxygen you breathe.
So if someone is tested for COHb levels some hours after exposure, those levels will have FALLEN.
COHb testing is like any other clinical investigation- it must be used judiciously and interpreted in light of other clinical findings. As always, an accurate history is often more inportant than getting a high COHb reading. If someone has symptoms suggestive of exposure, and if those symptoms are worse when they are inside their house, those findings are much more important than getting them to score on a CO-oximeter or a breath meter.

What has hyperbaric treatment to offer?

2006-11-17T13:12:00.000Z

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.

Cases in the news

2006-11-17T10:17:00.001Z

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.

Optic and other neuritides

2006-11-17T10:17:00.000Z

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.

CO - what is it

2006-11-15T16:55:00.000Z

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)

2006-11-15T16:35:00.000Z

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?

2006-11-13T19:28:00.000Z

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

2006-11-12T03:54:00.000Z

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.

The pulse oximtery problem

2006-11-10T19:01:00.002Z

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.

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

2006-11-10T19:01:00.001Z

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.

What are the symptoms?

2006-11-10T19:01:00.000Z

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.

CO doesn't only poison your blood

2006-11-09T16:17:00.000Z

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!

2006-11-09T16:16:00.001Z

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?

2006-11-09T14:19:00.000Z

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.

2006-11-09T11:37:00.000Z

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!

2006-11-09T11:02:00.000Z

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.'

2006-11-06T16:04:00.000Z

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 ?

2006-11-06T14:07:00.000Z

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.