History

Carbon monoxide (CO) toxicity is often misdiagnosed because of the vagueness and broad spectrum of complaints; symptoms often are attributed to a viral illness. Specifically inquiring about possible exposures when considering the diagnosis is important (see Overview/Practice Essentials and Overview/Etiology).

For nonfatal nonintentional non–fire-related exposures, the most common symptom was headache (37%) followed by dizziness (18%) and nausea (17%).^[13]However, any of the following symptoms should alert suspicion in the winter months, especially when the patient has a history compatible with CO exposure and when more than one patient in a group or household presents with similar complaints:

Malaise, flulike symptoms, fatigue
Dyspnea on exertion
Chest pain, palpitations
Lethargy
Confusion
Depression
Impulsiveness
Distractibility
Hallucination, confabulation
Agitation
Nausea, vomiting, diarrhea
Abdominal pain
Headache, drowsiness
Dizziness, weakness, confusion
Visual disturbance, syncope, seizure
Fecal and urinary incontinence
Memory and gait disturbances
Bizarre neurologic symptoms, coma

Chronic exposure also produces the above symptoms; however, patients with chronic CO exposure may present with loss of dentition, gradual-onset neuropsychiatric symptoms, or, simply, recent impairment of cognitive ability.

Physical Examination

Physical examination is of limited value. Inhalation injury or burns should always alert the clinician to the possibility of CO exposure.

Vital signs may include the following:

Tachycardia
Hypertension or hypotension
Hyperthermia
Marked tachypnea (rare; severe intoxication often associated with mild or no tachypnea)

Although so-called cherry-red skin has traditionally been considered a sign of CO poisoning (ie, "When you're cherry red, you're dead"), it is in fact rare.^[3] Pallor is present more often.

Ophthalmologic findings include the following:

Flame-shaped retinal hemorrhages
Bright red retinal veins (a sensitive early sign)
Papilledema
Homonymous hemianopsia
Noncardiogenic pulmonary edema

Neurologic and/or neuropsychiatric findings may include the following;

Memory disturbance (most common), including retrograde and anterograde amnesia with amnestic confabulatory states
Emotional lability, impaired judgment, and decreased cognitive ability
Stupor, coma, gait disturbance, movement disorders, and rigidity
Brisk reflexes, apraxia, agnosia, tic disorders, hearing and vestibular dysfunction, blindness, psychosis

Long-term exposures or severe acute exposures frequently result in long-term neuropsychiatric sequelae. Additionally, some individuals develop delayed neuropsychiatric symptoms, often after severe intoxications associated with coma.

After recovery from the initial incident, patients present several days to weeks later with neuropsychiatric symptoms such as those just described. Two thirds of patients eventually recover completely.

Differential Diagnoses

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Media Gallery

Monoplace hyperbaric chamber. Courtesy JG Benitez, MD, MPH.

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Author

Guy N Shochat, MD Associate Clinical Professor of Emergency Medicine, University of California, San Francisco, School of Medicine

Guy N Shochat, MD is a member of the following medical societies: Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Coauthor(s)

Michael Lucchesi, MD Chair, Associate Professor, Department of Emergency Medicine, State University of New York Downstate Medical Center

Michael Lucchesi, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

John T VanDeVoort, PharmD Regional Director of Pharmacy, Sacred Heart and St Joseph's Hospitals

John T VanDeVoort, PharmD is a member of the following medical societies: American Society of Health-System Pharmacists

Disclosure: Nothing to disclose.

John G Benitez, MD, MPH Associate Professor, Department of Medicine, Medical Toxicology, Vanderbilt University Medical Center; Managing Director, Tennessee Poison Center

John G Benitez, MD, MPH is a member of the following medical societies: American Academy of Clinical Toxicology, American Academy of Emergency Medicine, American College of Medical Toxicology, American College of Preventive Medicine, Undersea and Hyperbaric Medical Society, Wilderness Medical Society, American College of Occupational and Environmental Medicine

Disclosure: Nothing to disclose.

Chief Editor

Gil Z Shlamovitz, MD, FACEP Professor of Clinical Emergency Medicine, Keck School of Medicine of the University of Southern California; Chief Medical Information Officer, Keck Medicine of USC

Gil Z Shlamovitz, MD, FACEP is a member of the following medical societies: American College of Emergency Physicians

Disclosure: Nothing to disclose.

Additional Contributors

Peter MC DeBlieux, MD Professor of Clinical Medicine and Pediatrics, Section of Pulmonary and Critical Care Medicine, Program Director, Department of Emergency Medicine, Louisiana State University School of Medicine in New Orleans

Peter MC DeBlieux, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, Radiological Society of North America, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Asim Tarabar, MD Assistant Professor, Director, Medical Toxicology, Department of Emergency Medicine, Yale University School of Medicine; Consulting Staff, Department of Emergency Medicine, Yale-New Haven Hospital

Disclosure: Nothing to disclose.

Carbon Monoxide Toxicity Clinical Presentation

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