# Carbon Monoxide Poisoning

Carbon monoxide poisoning is a time-sensitive clinical diagnosis requiring immediate oxygen therapy, co-oximetry confirmation, cardiopulmonary assessment, and selective hyperbaric consultation. Carboxyhemoglobin supports exposure but does not grade injury reliably after oxygen or delayed presentation; neurologic and cardiac findings drive disposition.

**Clinical question:** How should physicians diagnose, risk-stratify, and manage suspected acute carbon monoxide poisoning?

Updated: 2026-08-21T00:02:59.203925Z

## What matters in practice
- Treat suspected poisoning immediately with high-flow 100% oxygen and resuscitative airway, ventilatory, circulatory, and seizure support; do not await confirmatory testing when clinical suspicion is high. [5][7]
- Diagnosis rests on compatible exposure, symptoms or signs, and elevated COHb measured by blood co-oximetry; a low COHb after prehospital oxygen or delayed sampling does not exclude clinically important poisoning. [7][12][14]
- For enclosed-space fire exposure, assess concurrently for cyanide toxicity. Altered mental status, soot exposure, and lactate at least 10 mmol/L support empiric hydroxocobalamin; treatment should not wait for lactate or cyanide results. [5][13]
- Obtain ECG and serial troponin in CO poisoning, because myocardial injury may be clinically silent and is associated with approximately threefold greater long-term mortality. [17]
- Hyperbaric oxygen is a selective therapy for severe poisoning and is intended to reduce persistent neurocognitive injury; the supplied sources support consideration in selected patients but do not provide a single universally accepted threshold-based referral rule. [7][24]

## Stabilize and begin oxygen before confirmation

Management should proceed from the exposure history and physiologic threat, not from pulse oximetry or a delayed COHb result.

Remove the patient from exposure, administer 100% oxygen, and provide immediate airway, ventilatory, circulatory, and seizure support as indicated. High-flow oxygen and supportive therapy are core treatment; hyperbaric oxygen should be considered selectively to reduce risk of persistent neurocognitive dysfunction. [5][7]

Use 100% oxygen even when PaO2 or conventional pulse oximetry appears reassuring: CO causes tissue hypoxia through carboxyhemoglobin formation and impaired cellular respiration, while standard oxygenation measures may not represent oxygen content or tissue delivery. [7][17]

Early toxicology or regional poison-center consultation is appropriate for severe exposure, neurologic deficits, pregnancy, smoke inhalation, suspected cyanide co-poisoning, or uncertainty regarding hyperbaric transfer. The U.S. poison-center access number is 1-800-222-1222. [5][13]
- Do not delay oxygen while obtaining COHb, lactate, ECG, or imaging. [5][7]
- Treat concurrent trauma, burns, inhalational airway injury, dysrhythmia, acute coronary syndrome, and shock by standard emergency pathways while addressing CO exposure. [5][17]
- For cardiac arrest, follow standard advanced life support; severe poisoning requires targeted toxicologic management in addition to routine resuscitation. [13]

*Immediate priorities in suspected carbon monoxide poisoning. [5][7][13]*

| Clinical problem | Immediate action | Critical interpretation |
| --- | --- | --- |
| Suspected CO exposure with compatible illness | Remove from source; administer 100% oxygen; stabilize airway, breathing, circulation, and seizures. [5][7] | Do not wait for COHb confirmation when suspicion is high. [5] |
| Enclosed-space fire with neurologic impairment or shock | Evaluate for cyanide toxicity and consider empiric hydroxocobalamin while providing oxygen and resuscitation. [5][13] | CO and cyanide co-poisoning are common after smoke inhalation. [13] |
| Possible severe neurologic injury | Obtain urgent hyperbaric-capable consultation while continuing oxygen and stabilization. [7][24] | Hyperbaric treatment is selective; transfer decisions should not delay life-saving stabilization. [7] |

## Confirm exposure with co-oximetry, but interpret COHb in context

COHb is useful for exposure confirmation, not a stand-alone severity or disposition test.

Diagnosis is based on the combination of a credible exposure history, compatible findings, and elevated carboxyhemoglobin. Whole-blood COHb measured by laboratory co-oximetry is the principal confirmatory test. [7][8]

A low or declining COHb does not safely exclude poisoning after oxygen therapy, delayed presentation, or transfer from another facility. Fatal and clinically important CO poisoning can occur with low measured COHb, and COHb correlates imperfectly with clinical severity and prognosis. [12][14]

Noninvasive pulse CO-oximetry may provide adjunctive screening information at baseline but should not replace blood COHb measurement. In a prospective study of 81 patients, SpCO demonstrated substantial bias and limited agreement with arterial COHb, especially at higher levels and after hyperbaric treatment. [11]
- Obtain blood co-oximetry as early as feasible, ideally before prolonged oxygen exposure when this does not delay treatment. [5][7]
- Document exposure source, enclosed versus open setting, duration estimate, time since removal, prehospital oxygen, smoking status, co-exposed persons, and potential intent. [6][7]
- Do not use conventional pulse oximetry to rule out CO poisoning; blood co-oximetry is required to quantify COHb. [8][11]

### Smoke inhalation and cyanide co-toxicity

In smoke inhalation, cyanide diagnosis is usually clinical because a rapid, widely available confirmatory blood test is lacking. The Cyanokit label identifies enclosed-space fire exposure, soot around the mouth, nose, or oropharynx, and altered mental status as key features; hypotension and plasma lactate at least 10 mmol/L increase concern, but therapy should not be delayed for lactate testing. [5]
- For suspected cyanide poisoning, hydroxocobalamin is FDA-labeled for known or suspected poisoning; give 5 g IV over 15 minutes in adults, with a second 5-g infusion if clinically indicated. [5]
- Hydroxocobalamin can cause transient hypertension, chromaturia, erythema, and interference with colorimetric laboratory tests; use a separate IV line when possible because of listed incompatibilities. [5]
- Avoid assuming that an elevated lactate in fire exposure is due solely to CO; CO and cyanide may coexist. [5][13]

*Diagnostic tests that alter early management in suspected CO poisoning. [5][7][11][17]*

| Test | Use | Actionable interpretation |
| --- | --- | --- |
| Blood COHb by co-oximetry | Confirms CO exposure and establishes a baseline when obtained early. [7][8] | Interpret with time since exposure and oxygen treatment; do not use alone to determine severity. [12][14] |
| ECG and serial troponin | Screen for ischemia, dysrhythmia, and myocardial injury. [17] | Cardiac abnormalities or troponin elevation warrant monitoring and cardiac evaluation. [17] |
| BNP or NT-proBNP | Adjunct marker of CO-associated myocardial dysfunction. [17] | Elevation supports echocardiographic assessment when available. [17] |
| Lactate and acid-base assessment | Defines severity of systemic illness and supports concern for cyanide in smoke inhalation. [5][13] | Lactate at least 10 mmol/L in smoke inhalation supports cyanide concern; do not delay antidote for this result. [5] |
| SpCO | Potential adjunctive screening only. [11] | Do not substitute for blood COHb, particularly after treatment. [11] |

## Neurologic and cardiac injury determine severity more reliably than COHb

Disposition should reflect organ injury, exposure context, response to oxygen, and need for hyperbaric assessment.

Severe poisoning may produce myocardial ischemia or infarction, ventricular or supraventricular dysrhythmias, cardiac dysfunction, syncope, seizures, coma, and stroke-like deficits. [7][17]

CO-related myocardial injury is prognostically important. In the reviewed literature, troponin elevation occurs in 17% to 37% of patients, and myocardial injury after moderate-to-severe poisoning is associated with approximately threefold greater long-term mortality. [17]

For active smokers hospitalized with acute cardiac events, exhaled CO greater than 11 ppm was associated with higher in-hospital major adverse events and 1-year all-cause mortality in a French observational cohort. This threshold is prognostic within that cohort and is not a diagnostic threshold for acute environmental CO poisoning. [6]
- Use continuous cardiac monitoring for patients with cardiac symptoms, ECG abnormalities, troponin elevation, syncope, dysrhythmia, hemodynamic instability, or severe exposure. [17]
- Obtain bedside or formal transthoracic echocardiography when myocardial injury is suspected; global dysfunction and takotsubo patterns have been described after CO poisoning. [17]
- Evaluate ST-elevation myocardial infarction with urgent cardiology involvement and coronary angiography when ECG and regional wall-motion findings are concordant. [17]

### Hyperbaric oxygen consultation

The supplied evidence supports high-flow oxygen for all patients and hyperbaric oxygen consideration for selected severe presentations, particularly when the goal is prevention of long-term neurocognitive dysfunction. [7][24] The evidence base remains debated; available sources do not establish a universally agreed COHb threshold for referral, and COHb alone should not determine eligibility. [7][24]
- Escalate early for hyperbaric consultation when there are major neurologic manifestations, loss of consciousness, severe cardiac involvement, pregnancy, or persistent clinically significant symptoms despite oxygen; these are severity-driven decisions rather than a substitute for resuscitation. [7][17][24]
- Hyperbaric access can be limited; FDA notes that hyperbaric facilities are geographically sparse, so do not postpone 100% oxygen and stabilization while arranging consultation or transfer. [3]
- Do not use post-treatment SpCO as the sole reassessment method after hyperbaric therapy; arterial COHb remains necessary when laboratory reassessment is clinically required. [11]

*Clinical features supporting admission, monitored care, and specialist consultation. [7][17][24]*

| Finding | Why it matters | Next step |
| --- | --- | --- |
| Altered mental status, syncope, seizure, coma, focal deficit | Signals acute CNS injury and risk of persistent neurocognitive sequelae. [7] | Admit or observe in a monitored setting; seek hyperbaric and toxicology input. [7][24] |
| Ischemic ECG changes, dysrhythmia, elevated troponin, ventricular dysfunction | CO-related myocardial injury may be occult and carries adverse long-term prognostic implications. [17] | Telemetry, serial ECG/troponin, echocardiography, and cardiology evaluation as indicated. [17] |
| Enclosed-space fire with soot and altered mentation | Raises concern for simultaneous cyanide toxicity. [5][13] | Administer oxygen, obtain lactate, and consider empiric hydroxocobalamin without delaying for confirmatory testing. [5] |
| Pregnancy | Fetal CO burden may exceed maternal burden and clear more slowly. [17] | Urgent obstetric and toxicology/hyperbaric consultation; assess maternal cardiac injury similarly to nonpregnant patients. [17] |

## Screen early for myocardial injury and arrange targeted follow-up

Cardiac injury can be clinically silent, transient on initial testing, and still associated with late risk.

A practical cardiac assessment includes ECG, troponin I, BNP or NT-proBNP, and transthoracic echocardiography or focused cardiac ultrasound. A 2024 review recommends initial screening of all CO-poisoned patients for cardiac impairment because injury can occur without cardiac symptoms. [17]

Repeat troponin over 6 to 12 hours after the initial measurement when myocardial injury is a concern. In one cohort summarized in the review, troponin peaked at approximately 11 hours and normalized at a median of 65 hours. [17]

Cardiac magnetic resonance may identify myocardial fibrosis in patients with elevated troponin despite a nonrevealing echocardiogram. This is a proposed expert-review strategy rather than a universally validated U.S. standard, and availability and acute clinical priorities should govern use. [17]
- If initial cardiac abnormalities are present, repeat ECG and echocardiography according to clinical course and monitor new ECG abnormalities until normalization. [17]
- For CO-induced LVEF at or below 40%, the JACC review advises applying general heart failure with reduced ejection fraction treatment principles; this recommendation is extrapolated rather than established specifically for CO cardiomyopathy. [17]
- The review proposes cardiac re-evaluation at 2 to 4 weeks and 6 months after poisoning for patients with myocardial injury; use Holter monitoring when arrhythmia has occurred. [17]

*Cardiac assessment strategy after acute CO poisoning. [17]*

| Phase | Assessment | Purpose |
| --- | --- | --- |
| Emergency evaluation | ECG, troponin I, BNP or NT-proBNP, and TTE or focused cardiac ultrasound. [17] | Identify ischemia, dysrhythmia, biomarker-defined injury, ventricular dysfunction, takotsubo pattern, or thrombus. [17] |
| Early reassessment | Repeat troponin at 6-12 hours when injury is suspected; continue ECG monitoring for new abnormalities. [17] | Detect delayed biomarker rise and evolving dysrhythmia or ischemia. [17] |
| Specialized imaging | Consider CMR with elevated troponin, including when echocardiography is unrevealing. [17] | Detect occult fibrosis or characterize ischemic versus nonischemic injury patterns. [17] |
| Post-discharge after myocardial injury | Cardiology reassessment at 2-4 weeks and 6 months; consider ambulatory rhythm monitoring after arrhythmia. [17] | Assess recovery, late cardiomyopathy, and conduction or rhythm complications. [17] |

## Prevent recurrent exposure and address intent before discharge

The next clinical event may affect household members, not only the index patient.

Before discharge, identify and eliminate the exposure source and ensure the patient will not return to an unsafe environment. Common sources include malfunctioning fuel-burning heating systems, gas stoves, engines or generators in poorly ventilated spaces, charcoal burning, and fires. [3][7]

For prevention, the JACC review cites CDC advice to install battery-operated or battery-backup CO detectors near sleeping areas, arrange annual inspection of oil or gas furnaces, and use portable gas generators more than 20 feet from the home and never indoors or in a garage. [17]

Intentional exposure requires psychiatric risk assessment after medical stabilization. Affected cohabitants, first responders, and pets may require exposure assessment; notify appropriate public health, fire, utility, or building authorities when an ongoing shared exposure is possible. The supplied sources emphasize diverse household and disaster-related exposure settings. [3][7][17]
- Advise smoking cessation when relevant; cigarette combustion increases CO burden and can confound interpretation of CO exposure measures. [6][12]
- Provide explicit return precautions for recurrent headache, confusion, syncope, chest pain, dyspnea, palpitations, or delayed cognitive and behavioral symptoms. Delayed neurologic sequelae are a recognized concern after CO poisoning. [7][14]

*Discharge readiness and prevention actions. [7][17]*

| Domain | Action before discharge |
| --- | --- |
| Exposure control | Confirm source evaluation and a safe alternative location if remediation is incomplete. [7][17] |
| Household prevention | Recommend functioning CO detectors near sleeping areas and annual inspection of fuel-burning equipment. [17] |
| High-risk recurrence | Assess intentionality, substance use, and psychosocial safety; arrange appropriate behavioral health follow-up when indicated. [7] |
| Medical follow-up | Arrange neurologic or cardiac follow-up based on acute injury, symptoms, ECG, biomarkers, and ventricular function. [17] |

## Common questions

### Does a normal pulse oximetry reading exclude carbon monoxide poisoning?

No. Conventional pulse oximetry does not quantify COHb or reliably reflect oxygen content in dyshemoglobinemia. Confirm suspected exposure with blood co-oximetry and treat according to clinical severity. [7][8][11]

### Can a low carboxyhemoglobin level exclude serious carbon monoxide poisoning?

No. COHb may fall rapidly after oxygen therapy or delayed presentation, and low measured values have been documented in clinically important and fatal CO poisoning. Interpret COHb with exposure timing and clinical injury. [12][14]

### When should cyanide antidote be considered in a fire victim?

Consider empiric hydroxocobalamin for suspected cyanide poisoning after enclosed-space fire exposure with soot, altered mental status, hemodynamic compromise, severe acidosis, or lactate at least 10 mmol/L. Do not delay treatment for cyanide confirmation. [5][13]

### Who needs cardiac testing after carbon monoxide poisoning?

The supplied JACC review recommends ECG, troponin, natriuretic peptide testing, and echocardiographic assessment because CO-related myocardial injury may be asymptomatic and is associated with adverse long-term risk. [17]

### Is hyperbaric oxygen indicated solely because the COHb is elevated?

No. The supplied sources support selective hyperbaric consideration for severe poisoning and neurocognitive-risk reduction, while emphasizing that COHb alone does not reliably define injury severity or disposition. [7][12][24]

## References
1. FULL PRESCRIBING INFORMATION - accessdata.fda.gov — www.accessdata.fda.gov — https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/202067s002,203993s002lbl.pdf
2. 3610418 This label may not be the latest approved by FDA ... — www.accessdata.fda.gov — https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/022352s017lbl.pdf
3. FDA allows marketing of new device to help treat carbon monoxide poisoning | FDA — www.fda.gov — https://www.fda.gov/news-events/press-announcements/fda-allows-marketing-new-device-help-treat-carbon-monoxide-poisoning
4. Prescribing Information (PI) Potpourri — www.fda.gov — https://www.fda.gov/media/97736/download
5. Cyanokit Label - accessdata.fda.gov — www.accessdata.fda.gov — https://www.accessdata.fda.gov/drugsatfda_docs/label/2006/022041lbl.pdf
6. Carbon monoxide and prognosis in smokers hospitalised with acute cardiac events: a multicentre, prospective cohort study — www.thelancet.com — https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(23)00578-3/fulltext
7. Carbon monoxide poisoning - Symptoms, diagnosis and ... — bestpractice.bmj.com — https://bestpractice.bmj.com/topics/en-us/432
8. 1497 Methods to diagnose carbon monoxide exposure — emj.bmj.com — https://emj.bmj.com/content/39/12/A971.2
9. Global, regional, and national mortality due to unintentional ... — www.thelancet.com — https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(23)00185-8/fulltext
10. Dose adjustment in renal impairment: Response from Drug Prescribing in Renal Failure | The BMJ — www.bmj.com — https://www.bmj.com/content/331/7511/293.2
11. Agreement and clinical utility of non-invasive SpCO versus ... — www.nature.com — https://www.nature.com/articles/s41598-026-51424-y
12. Acute carbon monoxide poisoning with low saturation of ... — www.nature.com — https://www.nature.com/articles/s41598-021-97436-8
13. An Update to the American Heart Association Guidelines ... — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/CIR.0000000000001161
14. Analysis of prognosis of neurological sequelae in children ... — www.nature.com — https://www.nature.com/articles/s41598-024-81634-1
15. Abstract 4145376: Carbon Monoxide-Induced Atrial ... — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/circ.150.suppl_1.4145376
16. A scoring system with high predictive performance for poor ... — www.nature.com — https://www.nature.com/articles/s41598-025-98162-1
17. Practical Recommendations for the Evaluation and ... — www.jacc.org — https://www.jacc.org/doi/10.1016/j.jchf.2024.01.001
18. Cardiovascular Manifestations of Moderate to Severe ... — www.jacc.org — https://www.jacc.org/doi/10.1016/j.jacc.2005.01.044
19. An antidote for carbon monoxide poisoning? — www.science.org — https://www.science.org/content/article/antidote-carbon-monoxide-poisoning
20. Life-Threatening Acute Pulmonary Thromboembolism ... — www.jacc.org — https://www.jacc.org/doi/10.1016/j.jaccas.2019.05.024
21. fact sheet for healthcare providers: emergency use ... — go.nature.com — https://go.nature.com/3zbxvqg
22. Reply: Carbon Monoxide Treatment Guidelines Must ... — academic.oup.com — https://academic.oup.com/ajrccm/article/187/12/1390/8510223
23. Carbon Monoxide Treatment Guidelines Must Acknowledge ... — academic.oup.com — https://academic.oup.com/ajrccm/article/187/12/1390/8510221
24. Practice Recommendations in the Diagnosis, Management ... — academic.oup.com — https://academic.oup.com/ajrccm/article-abstract/186/11/1095/8507763

## Editorial note

Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.