So Bored, So She Passed Out Before Her Nap Time – CO Poisoning

co-001It’s still 1993. You are finishing up your rotation at the Bogota General Hospital in Colombia. It’s your last day. EMS rolls in a 40-year-old female who was found lying down on the floor of her apartment. The patient’s husband had come in and then found his wife minimally responsive. As per husband, his son was also acting “different” and looked confused. The patient does not have any significant past medical history or recent drug exposure. Upon further questioning, the husband tells you that yesterday he bought a new boiler, which he installed it in the basement.


You are suspecting CO poisoning.

What are the symptoms?

Symptoms may range from flu-like symptoms to coma:

-Headache (most common)



-Blurry vision


-Chest pain & cardiac dysrhythmias

-Lightheadedness/dizziness (2nd most common)

-Cutaneous blistering



What is the epidemiology of CO poisoning?

Carbon monoxide (CO) poisoning is responsible for up to 40,000 emergency department (ED) visits and 5000 to 6000 deaths per year. Unlike intentional poisoning, unintended poisoning demonstrates both seasonal and regional variation, and it is most common during the winter months in cold climates

How do you measure CO levels?

CO poisoning can be diagnosed by directly measuring carboxyhemoglobin percentage (COHb). Note that the percentage does not correlate with signs and symptoms.  

You sent patient’s venous blood gas level, and CO level is elevated at 16%.

How do you interpret COHb?

-Nonsmoker living outside of urban area ~ 0.4-1.0%

-Nonsmoker living in an urban area ~ ≤ 5%

-Heavy chronic smoker ~ ≤ 15%

-Mild CO poisoning ~ >10% with no clinical signs and symptoms

-Moderate CO poisoning ~ >10% with clinical signs and symptoms

-Severe CO poisoning ~ > 20% with confusion, altered mental status, loss of consciousness, or signs of cardiac ischemia

You start the patient on oxygen therapy via a non-rebreather oxygen mask. Is this enough? How much oxygen is needed, for how long?

Oxygen administration enhances the elimination of CO from the body by decreasing the elimination CO half-life.

CO half-life

Room Air

4-5 hours

100% O2 by non-rebreather mask

~ 1 hour

Hyperbaric Oxygen

~ 20 minutes

What are indications for hyperbaric oxygen (HBO) therapy?

The Undersea and Hyperbaric Medical Society recommends HBO therapy for patients with any of the following:

-Focal neurological findings

-Severe acidosis


-Acute myocardial infarction

-CO exposure of >24 hours

-Carboxyhemoglobin level > 25%

-Pregnancy w/ carboxyhemoglobin level >15%

*The goal of treatment with hyperbaric oxygen is the prevention of long-term and permanent neurocognitive dysfunction, rather than the enhancement of short-term survival rates. However, the use of hyperbaric oxygen remains controversial, and systematic reviews have highlighted the need for further research to define its role.

What are long term symptoms of CO poisoning (if not adequately treated)?

Delayed neurological sequelae (DNS): Can occur days to weeks after apparent resolution of acute symptoms in up to 46% of patients. Patients can present with progressive dementia, psychosis, motor disturbances, ataxia, and long-term cognitive deficits.

Bonus: What would you expect to find on imaging in patients with long-term CO poisoning?

On MRI, you may see symmetric abnormal signal within the deep gray matter (most commonly the globus pallidus)

The images below show MRI of a patient who presented to emergency department with a 5-month history of progressive dementia. She was initially worked up for different neurological and psychiatric diseases; however, upon further investigation, it was found that 6 months ago her house was burned down.



Thanks to Dr. deSouza, and Dr. Willis.



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PGY-2 Emergency Medicine. Kings County Hospital/SUNY Downstate Medical Center.

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