Toxicology Sessions – Carbon Monoxide

Sign in or subscribe to listen

No me gusta!

The flash player was unable to start. If you have a flash blocker then try unblocking the flash content - it should be visible below.

Nurses Edition Commentary

Kathy Garvin, RN and Lisa Chavez, RN

No me gusta!

The flash player was unable to start. If you have a flash blocker then try unblocking the flash content - it should be visible below.

Siamak M, MD -

Hi Sean, I'm a Hyperbaric/EM physician and I (nor any of my colleagues) had not heard about the comments you made about fetal Hgb and CO. Can you please share your references so that we can look into updating our pregnant CO toxicity treatment guidelines? Thanks.

Sean N. -

Thank you for message Simak. Great to hear from you.

Treatment of pregnant patients is difficult in carbon monoxide poisoning as you know. The initial concern of fetal hemoglobin being a "sink" was based on animal data but not thought to be truly accurate in humans.

Maternal carboxyhemoglobin levels are not good predictors of fetal carboxyhemoglobin levels. As a hyperbaricist who will be managing these cases I suggest you and your group discuss with your local toxicologists and/or poison center to make sure you are all on same page as your local group may feel diving at lower level is warranted before change any protocols.

The key to any patient with carbon monoxide poisoning and considering hyperbarics is in symptomatic patients including fetal distress at any concentration. As you have seen I am sure in your practice patients can have a relatively low level and be very symptomatic. Often pregnant patients have additional physical findings to consider hyperbarics beyond the pregnancy alone.

From Table in Goldfrank's Toxicologic Emergencies 10th edition on Suggested Indications for Hyperbaric Oxygen

Syncope (loss of consciousness)
Altered mental status (GCS<15) or confusion
Carboxyhemoglobin >25%
Abnormal cerebellar function
Age ≥36 years
Prolonged CO exposure (≥24 hours)
Fetal distress in pregnancy

Fetal Distress in Pregnancy is listed rather than a lower maternal carboxyhemoglobin level.

For specific references I suggest you and your group review the chapter and individual references in Goldfrank's Toxicologic Emergencies 10th edition on Carbon Monoxide Section on Hyperbaric Oxygen Subsection Treatment of Pregnant Patients by Chris Tomaszweski. He is an emergency physician who is also toxicologist and hyperbaricist.

Of course your clinical impression of an individual patient trumps all else when considering who may benefit from hyperbarics in carbon monoxide poisoning. Dr. Tomaszweski does a nice review specifically on the basis for the initial concerns based on the animal model.

Hope that is useful.

Sean N. -

To all clinicians treating carbon monoxide poisoning including pregnant patients I recommend consulting your local toxicologist and/or poison control center for the specific management of your individual patient or patients including if your patient or patients may benefit from hyperbaric oxygen therapy. Carbon monoxide is a complex poisoning and benefits from the additional expertise of medical toxicology and/or poison center consultation.

Joel R. -

So, last time that I called poison control, they recommended me placing the patient on high flow nasal cannula instead of a NRB mask. Anyone else heard of this? It worked well and made sense, blew down a level of approximately 30% quite well.

Sean N. -

Hi Joel thank you for the message
My recommendation is 100% non-rebreather face mask with high flow oxygen. Many of these patients are going to be symptomatic and hypoxic at a cellular level as carbon monoxide impairs oxygen delivery. Standard pulse oximeters are not accurate in carbon monoxide poisoning and should not be relied upon and these patients can have elevated carboxyhemoglobin levels with normal oxygen saturation reading. As with other therapies using oxygen there is the consideration that “excess” oxygen may cause cellular damage from hyperoxia. This may be the basis of the recommendation you received about using nasal cannula although without knowing the specifics of their recommendation in the case you had hard to comment. That being said I recommend starting high flow oxygen by non-rebreather face mask particularly early in treatment and in symptomatic patients and those with elevated carboxyhemoglobin levels or if levels pending and clinically suspect. Follow carboxyhemoglobin levels as you did in your case.

J. B. L. -

I remember on my boards - about 25 years ago there was a chemical that was metabolized to CO i n the body - I think it was called methylene chloride - is this chemical still used? how would this be treated- same way?

Sean N. -


Thank you for the message.

Yes you are correct and yes carbon monoxide poisoning from methylene chloride is treated the same way.

Methylene chloride also known as Dichloromethane is a solvent used in many industries and uses include: paint stripping, pharmaceutical manufacturing, paint remover manufacturing, metal cleaning and degreasing, adhesives manufacturing and use, polyurethane foam production.

Methylene chloride when inhaled or ingested is converted in the body to carbon monoxide. This can be a challenging often these people are found unconscious without a running engine or heater, etc. and therefore carbon monoxide is not thought considered.

Though there are occupational hazards with persons using methylene chloride without proper protection the majority of deaths have been from the home use of using paint strippers containing methylene chloride, particularly in closed spaces and without protection eg, basement, garage.

The conversion to carbon monoxide takes several hours.

Any patient found unconscious without obvious cause or confirmed reason should have a VBG to measure carboxyhemoglobin level.

There has been a push for the EPA to ban paint strippers containing methylene chloride from unintentional deaths from carbon monoxide poisoning but also concerns of longer term chronic exposure.

Colin K. -


Thanks for your lecture. Great points! The only things I can add as a BC hyperbaric and ED physician are the following:
1. In our particular system (The Ohio State University Wexner Medical Center), the referral calls come to the HBO doc on call and only rarely to the toxicologist at the local poison center. We are the ones making the recommendations in our particular system.
2. A non-rebreather mask can only deliver an Fi02 in the 60% range so to get to a "93% NRB" you have to set up similar to preoxygenation with a NC at 15 LPM plus an NRB at flush (50 LPM). Most patients hate this, especially if not humidification is provided,
3. ACEP's guidelines on HBO were very strategically developed to avoid making HBO a strongly recommended therapy so as to keep the ED physician who has limited access to HBO from being accused of breaching a standard of care by not transferring or treating all cases with HBO, This seems like the right way to approach this issue. I have traditionally not treated just based on a number, but more because of the degree of symptoms the patient experienced,
4. With regard to pregnancy, as you said, Goldfrank's Toxicology discussed fetal hemoglobin having a lower affinity for CO (a ratio of 0.8), but they do state that fetal hypoxia can become an issue in maternal CO poisoning. They still recommend using 15% as a cutoff. From the text: "Thus, it appears that HBO should be safe and have the same efficacy for pregnant patients as in nonpregnant patients. There currently is no scientific validation for an absolute level at which to provide HBO therapy for a pregnant patient with CO exposure. Somewhat arbitrarily, we recommend a threshold for HBO in pregnant patients is a COHb level regardless of symptoms of greater then or equal to 15%."

For the person asking about references from Goldfrank: Westphal M, et al. Affinity of carbon monoxide to hemoglobin increases at low oxygen fractions. Biochem Biophys Res Commun. 2002;295:975–977. [PubMed: 12127991]
Ginsberg MD, Myers RE. Fetal brain injury after maternal carbon monoxide intoxication. Clinical and neuropathologic aspects. Neurology. 1976;26:15–23.

Ben S. -


What are your thoughts on bedside co-oximeters? We recently had a missed case with one of these -

Sean N. -

Hi Colin,

Thank you for your comments…and great speaking to you too. (Colin and I have collaborated on “Bouncebacks” with Mike Weinstock previously). Please see below.

1. Yes, I agree with you, there are many centers where it is hyperbaric physicians who are the consultants on carbon monoxide cases, others where it is medical toxicology physicians and others where combination of both. For these reasons when and who to dive recommendations may be provider and institution specific.

I recommend everyone be familiar with the closest HBO chamber in your area and the procedure for getting a consult. The poison center can usually facilitate this.

2. Thank you for highlighting that just because it is 100% oxygen coming out of the wall does not mean that the lungs are receiving FiO2 100%. Your points are well taken about patient comfort issues with both tight fitting NRBFM compared to NC and that oxygen should be humidified. These poisonings can be emotionally devastating for patients as often multiple family members are involved, some may have been found dead, and patient comfort should be emphasized and doing best to ensure best treatment.
3. I agree with you also about having the challenges of ACEP guidelines having HBO being strongly recommended as the standard of care due to the wide variation of availability of hyperbarics in many areas. I believe the major reason for not declaring standard of care is the guidelines need to be supported in the literature and these studies are challenging to do and often have conflicting results and various dive protocols used. If HBO does become the standard of care we definitely will need a whole lot more HBO chambers and in relatively close proximity to most emergency departments. Another challenge is many of these severe poisonings occur in winter months where transferring by land or air may be hazardous due to travel conditions and may involve long transfer times, which can be challenging with often critically ill patients and the patients who present late.

I also agree with your statement about “not treat(ing) just based on a number, but more because of the degree of symptoms the patient experienced.”

We have all seen two different patients, one who was found unconscious in a residence after 24 hours or more of continuous carbon monoxide who may be comatose at a level of COHb 25% and another who may have been rescued from a structural fire with a relatively short exposure period to carbon monoxide who has a COHb level of 25% too and may be minimally symptomatic. These may not always be considered the same prognostically despite the same numbers. Again, this demonstrates the complexity of these poisonings.

My recommendation is clinicians should obtain expert consultant guidance with all carbon monoxide poisonings.

4. Thank you for the references and mentioning Goldfrank’s. The passage you include is from the brand new 2019 Goldfrank’s Toxicologic Emergencies 11th edition, which has come out since we recorded the carbon monoxide piece. What is interesting is Goldfrank’s in this latest edition has added the line you mentioned. “Somewhat arbitrarily, we recommend a threshold for HBO in pregnant patients is a COHb level regardless of symptoms of greater than or equal to 15%." This was not in the Goldfrank’s 10th edition but was added to the most recent 11th edition. This revision, and I appreciate the qualifier “arbitrarily”, most likely were added to err on the side of treatment in the pregnant patient as carbon monoxide has been associated with fetal loss. Some other centers may use 20% or higher or base on symptoms alone. Using 15% will definitely capture more pregnant patients and is prudent. At these levels in pregnant patients ie, COHb 15% I am recommending prompt consultation for consideration of HBO to ensure potential treatment in these patients. Of course, maternal and/or fetal distress or compromise at any level should prompt consideration of HBO.

My current recommendation is for clinicians to consult experts in carbon monoxide eg, medical toxicologists, hyperbaricists, poison center in ALL carbon monoxide poisonings including ALL pregnant patients. These poisonings are very complex and often challenging clinically.

Sean N. -

Hi Ben S.

Great to hear from you.

I would like to hear more about your "missed" case.

I did publish a mass casualty incidence based on incorrect reading from hand held co-oximeter although this was operator error in the field. Citation below.

These portable hand held devices are FDA approved for their indications based on clinical data and as such should be accurate but as above may be operator dependent. Was this the issue in your case?

My recommendation is if a clinician is concerned about carbon monoxide poisoning in the emergency department is to get a VBG measuring COHb.

Mass sociogenic illness initially reported as carbon monoxide poisoning.
J Emerg Med. 2012 Feb;42(2):159-61.

We had 22 patients transferred to EDs from an incorrect reading of handheld co-oximeter. One of prehospital personnel read eg, 1.9% as 19% in multiple patients prompting the mass casualty incident.

To join the conversation, you need to subscribe.

Sign up today for full access to all episodes and to join the conversation.