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<< Diagnosis And Management Of Carbon Monoxide Poisoning In The Emergency Department

Emergency Department Evaluation

Initial Stabilization

Patients with confirmed or strongly suspected CO poisoning may be triaged according to their clinical status. Special attention must be paid to airway management. As discussed above, co-inhalants from fires may lead to impending airway compromise. Patients with thermal or chemical injury to the pulmonary system or upper airways may require urgent intubation on the basis of their expected clinical course. Non-invasive co-oximetry may be useful at triage to rapidly identify patients with significant CO exposure. Patients should receive high-flow oxygen. Vital signs and a directed neurologic examination should be done frequently, and the patient should have continuous cardiac monitoring. An IV catheter should be inserted. Laboratory studies, including a COHb level by cooximetry, should be ordered. This may be obtained from an arterial blood gas if acid-base disturbance is suspected. Patients with alteration in mental status or complaints consistent with myocardial ischemia should have an ECG.


Clinical signs and symptoms of CO poisoning are non-specific and vary widely.1 Vague systemic symptoms such as fatigue, nausea or vomiting, or weakness may be the only indicators.

More severely poisoned patients may develop acute neuropsychological symptoms such as ataxia, seizure, syncope, coma, disorientation, and cognitive difficulties. Loss of consciousness is a marker of poisoning severity.16,19

Patient evaluation in suspected CO poisoning is directed at making the diagnosis, estimating the severity of poisoning, and identifying end-organ damage. Questions to ask include:

  • Where was the patient found, and under what circumstances?
  • Was there clear evidence of CO exposure?
  • Was there loss of consciousness?
  • Was there evidence of trauma?
  • Was a fingerstick glucose determination performed?
  • Was noninvasive co-oximetry performed?
  • Was prehospital ECG performed?
  • Was there evidence of attempted self-harm or suicidal intent?

In addition to performing a standard medical history, patients should be asked about symptoms consistent with end-organ dysfunction or damage. These include headaches, alterations in mentation or difficulty performing simple mathematical tasks, visual changes, syncope, other focal neurologic symptoms, or seizure. All patients, regardless of age or health status, should be asked about the presence of netchest pain, shortness of breath, dyspnea on exertion, palpitations, or lightheadedness. Female patients should be asked about the possibility of pregnancy. Finally, all patients with CO poisoning should be questioned directly regarding suicidal intent.6

Physical Examination

The key components of the physical examination in CO poisoning are the trauma, neurologic, and cardiovascular examinations. The former is focused on identifying concomitant injuries, especially in patients who are coming from the scene of a fire or in those who had syncope secondary to CO exposure. The latter 2 components of the examination are focused on identifying signs of end-organ toxicity due to acute CO poisoning.

A methodical approach to the evaluation of trauma is indicated, especially in patients with altered mental status. Several parts of the examination bear special attention in suspected CO poisoning. Patients coming from the scene of a fire are at risk for thermal injury and pursuant upper airway obstruction, so definitive airway management should be considered early in the patient’s hospital course. The oropharynx should be visualized to evaluate for edema and soot, and the neck should be carefully examined for the presence of stridor. Although hypotension in most trauma patients is often initially presumed to be from loss of circulating blood volume, CO-poisoned patients may have vasodilatory shock due to acidosis. Co-inhalants, such as cyanide, may present in the same manner, and these should not be overlooked in the differential diagnosis of the hypotensive patient, even while simultaneously treating with volume expansion. A careful pulmonary examination may detect small airways obstruction as wheezing in patients who are exposed to smoke or have inhaled other irritants. Patients may also have “cardiac wheezing” or crackles in the lungs, signifying myocardial depression secondary to smoke inhalation.

Any patient presenting with possible CO poisoning should undergo a formal assessment of mental status. In addition to typical orientation questions, it may be useful to perform a comprehensive mental status assessment. Carbon-monoxide- poisoned patients may present with cognitive changes, even in the acute phase of poisoning. Cranial nerves should be examined and a thorough motor and sensory examination performed to detect any focal neurologic deficits. Bedside tests of cerebellar function, such as finger-to-nose testing, heel-to-shin testing, or rapid alternating movements, may also detect abnormalities not evident on gross examination. Gait testing is a must, because ataxia can be a presenting sign of neurotoxicity and may be missed if the patient is not observed while ambulating.

The cardiac examination focuses on signs of myocardial ischemia and global hypoperfusion. Jugular venous pressure may be elevated, indicating acutely depressed cardiac function. A new gallop may represent acute diastolic dysfunction. Hypotension may indicate cardiogenic shock due to ischemia, or it may be related to acidosis and vasodilation.

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Last Modified: 11/23/2017
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