Carbon Monoxide Toxicity in Emergency Medicine Workup

  • Author: Guy N Shochat, MD; Chief Editor: Asim Tarabar, MD   more...
 
Updated: May 19, 2011
 

Laboratory Studies

  • HbCO analysis requires direct spectrophotometric measurement in specific blood gas analyzers. Bedside pulse CO-oximetry is now available but requires a special unit and is not a component of routine pulse oximetry.
    • Elevated levels are significant; however, low levels do not rule out exposure, especially if the patient already has received 100% oxygen or if significant time has elapsed since exposure.
    • Individuals who chronically smoke may have mildly elevated CO levels as high as 10%. Presence of fetal hemoglobin, as high as 30% at 3 months, may be read as an elevation of HbCO level to 7%.
  • Arterial blood gas
    • PaO2 levels should remain normal. Oxygen saturation is accurate only if directly measured but not if calculated from PaO2, which is common in many blood gas analyzers.
    • As with pulse oximetry, estimate PCO2 levels by subtracting the carboxyhemoglobin (HbCO) level from the calculated saturation. PCO2 level may be normal or slightly decreased. Metabolic acidosis occurs secondary to lactic acidosis from ischemia.
  • Troponin, creatinine kinase-MB fraction, myoglobin
    • Myocardial ischemia is frequently associated with patients hospitalized for moderate-to-severe CO exposure and is a predictor of mortality.[10]
    • Patients with preexisting disease can experience increased exertional angina with HbCO levels of just 5-10%. At high HbCO levels, even young healthy patients develop myocardial depression.
  • Creatinine kinase, urine myoglobin: Nontraumatic rhabdomyolysis can result from severe CO toxicity and can lead to acute renal failure.
  • Complete blood count
  • Electrolytes and glucose level - Lactic acidosis, hypokalemia, and hyperglycemia with severe intoxication
  • BUN and creatinine levels - Acute renal failure secondary to myoglobinuria
  • Liver function tests - Mild elevation in fulminant hepatic failure
  • Urinalysis - Positive for albumin and glucose in chronic intoxication
  • Methemoglobin level - Included in the differential diagnosis of cyanosis with low oxygen saturation but normal PaO2
  • Toxicology screen - For instances of suicide attempt
  • Ethanol level - A confounding factor of intentional and unintentional poisonings
  • Cyanide level - If cyanide toxicity also is suspected (eg, industrial fire); cyanide exposure suggested by an unexplained metabolic acidosis; rapid determinations rarely are available. Smoke inhalation is the most common cause of acute cyanide poisoning.
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Imaging Studies

  • Chest radiography
    • Obtain a chest radiograph with significant intoxications, pulmonary symptoms, evidence of hypoxia, or if hyperbaric oxygen is to be used.
    • Findings usually are normal.
    • Changes such as ground-glass appearance, perihilar haze, peribronchial cuffing, and intra-alveolar edema imply a worse prognosis than normal findings.
  • CT scan
    • Obtain a CT scan of the head with severe intoxication or change in mental status that does not resolve rapidly.
    • Assess cerebral edema and focal lesions; most are typically low-density lesions of the basal ganglia.
    • Positive CT scan findings generally predict neurologic complications.
    • In one study, 53% of patients hospitalized for acute CO intoxication had abnormal CT scan findings; all of these patients had neurologic sequelae. Of those patients with negative scan results, only 11% had neurologic sequelae.[11]
    • MRI is more accurate than CT scans for focal lesions and white matter demyelination and is often used for follow-up care.
    • Serial CT scans may be necessary, especially with mental status deterioration.
    • A recent report describes the evolution of acute hydrocephalus in a child poisoned with CO, documented by serial CT scans.
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Other Tests

  • Electrocardiogram
    • Sinus tachycardia is the most common abnormality.
    • Arrhythmias may be secondary to hypoxia, ischemia, or infarction.
    • Even low HbCO levels can have severe impact on patients with cardiovascular disease.
  • Neuropsychologic testing
    • Formal neuropsychologic testing of concentration, fine motor function, and problem solving consistently reveal subtle deficits in even mildly poisoned patients.
    • Abridged versions of these tests, more applicable to the emergency department (ED) setting, have been developed as possible means to assess the risk of delayed neurologic sequelae, to assess the need for hyperbaric oxygen therapy, and to determine the success of hyperbaric therapy in preventing delayed sequelae.
    • These tests are used in some institutions, but studies prospectively confirming the conclusions are lacking.
    • Abridged tests can be performed in about 30 minutes by a well-trained examiner.
    • Recent research indicates a specific link to deficits in context-aided memory; such specific testing has been proposed as a tool for measuring the severity of neurologic involvement in the ED.
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Contributor Information and Disclosures
Author

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

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 at Brooklyn

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

Disclosure: Nothing to disclose.

Specialty Editor Board

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, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

John T VanDeVoort, PharmD  Regional Director of Pharmacy, Sacred Heart & 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, Society for Academic Emergency Medicine, Undersea and Hyperbaric Medical Society, and Wilderness Medical Society

Disclosure: Nothing to disclose.

John D Halamka, MD, MS  Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center

John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Chief Editor

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.

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