Carbon Monoxide Toxicity Clinical Presentation

Updated: Jan 26, 2023
  • Author: Guy N Shochat, MD; Chief Editor: Gil Z Shlamovitz, MD, FACEP  more...
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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.