Updated: 5/2/2020

Carbon Monoxide Poisoning

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Snapshot
  • A 35-year-old painter presents to the emergency room for nausea, vomiting, and a headache. He reports that a large vat of paint thinner had spilled, and he had spent the afternoon cleaning it up. While at the time he felt fine, an hour after he finished, he started experiencing these symptoms. On physical exam, he is oriented to self and place but not the year. He is tachycardic with a pulse of 112/min.  Pulse oximetry reveals an oxygen saturation of 96% on room air. A CO-oximetry shows carboxyhemoglobin levels of 23%. He is started on 100% oxygen. A lactic acid level is drawn to assess for concomitant cyanide poisoning.
Introduction
  • Clinical definition
    • carbon monoxide (CO) poisoning results from exposure to CO resulting in hypoxia
  • Epidemiology
    • incidence
      • leading cause of death from unintentional poisoning
      • common in industrialized patients
    • risk factors
      • use of charcoal, gas, or petroleum
      • wood-burning heaters
      • cooking in poorly ventilated areas
      • building fires
      • smoke inhalation
      • motor vehicle exhaust
      • exposure to methylene chloride (paint thinners)
        • metabolized into CO
        • delayed CO poisoning
  • Pathogenesis
    • mechanism
      • displaces oxygen from hemoglobin
        • causes left-shift of oxygen-hemoglobin curve, leading to decreased delivery of oxygen to tissues
      • binds to cytochrome oxidase
        • disrupts electron transport chain
      • increases lipid peroxidation in the central nervous system
  • Associated conditions
    • cyanide poisoning
  • Prognosis
    • worse with very young or very old age
    • worse with prolonged or intentional exposures
Presentation
  • Symptoms
    • headache
    • lightheadedness
    • nausea and vomiting
    • improvement when removed from the exposure
  • Physical exam
    • normal pulse oximetry
    • tachycardia
    • dyspnea
    • altered mental status
      • confusion
    • cherry-red skin
      • late finding of CO poisoning
Studies
  • Diagnostic testing
    • studies
      • pulse oximetry
        • normal oxygen saturation level
      • ↑ carboxyhemoglobin (COHb) levels
        • must be assessed before supplemental oxygen is administered
          • arterial blood gas
          • venous blood gas
          • portable CO-oximetry devices (not regular pulse oximetry)
        • > 3% for nonsmokers
        • > 9% for smokers
      • lactic acid 
        • decreased delivery of oxygen to tissues
      • ↑ troponin
        • CO poisoning may cause myocardial injury due to relative hypoxemia
  • Making the diagnosis
    • based on clinical presentation and laboratory studies
      • carboxyhemoglobin levels > 20%
Differential
  • Cyanide poisoning
    • distinguishing factor
      • ↑ lactic acid
      • does not respond to oxygen therapy
Treatment
  • Management approach
    • remove all sources of CO from the patient
    • 100% or hyperbaric oxygen
  • First-line
    • 100% oxygen   
      • to displace CO from hemoglobin
      • decreases half-life of CO in most patients from 4-5 hours to 1 hour
      • decreases half-life of CO from methylene chloride from 13 hours to 6 hours
  • Second-line
    • hyperbaric oxygen 
      • indication
        • neurological deficits
        • pregnant women
        • children
        • elderly
        • significantly elevated COHb levels
        • methylene chloride as cause of CO poisoning
Complications
  • Myocarditis
  • Acute respiratory distress syndrome

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Questions (6)
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(M2.PL.17.4799) A 36-year-old male with fluctuating levels of consciousness is brought to the emergency department by ambulance due to a fire in his home. He currently opens his eyes to voice, localizes painful stimuli, responds when asked questions, but is disoriented and cannot obey commands. The patient’s temperature is 99°F (37.2°C), blood pressure is 86/52 mmHg, pulse is 88/min, and respirations are 14/min with an oxygen saturation of 97% O2 on room air. Physical exam shows evidence of soot around the patient’s nose and mouth, but no burns, airway obstruction, nor accessory muscle use. A blood lactate is 14 mmol/L. The patient is started on intravenous fluids.

What is the next best step in management?

QID: 109311
1

Methylene blue

0%

(0/31)

2

Hyperbaric oxygen

29%

(9/31)

3

Intravenous epinephrine

13%

(4/31)

4

Sodium thiosulfate and sodium nitrite

3%

(1/31)

5

100% oxygen and hydroxycobalamin

55%

(17/31)

M 7 D

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(M2.PL.14.132) A 42-year-old man with no significant medical history presents to the emergency department with complaints of headache, nausea, and dizziness. He states that he was at home working on his car when he started to feel dizzy and experienced a headache. This progressed to him feeling nauseous. The patient states he went inside and drank some water and felt better; however, when he started working on his car again his symptoms returned. Upon presentation, he states his symptoms have mostly improved except for a persistent headache. His temperature is 98.1°F (36.7°C), blood pressure is 125/84 mmHg, pulse is 87/min, respirations are 18/min, and oxygen saturation is 98% on room air. Neurologic exam is unremarkable. Which of the following is the best next step in management?

QID: 104772
1

100% oxygen

20%

(7/35)

2

CT

3%

(1/35)

3

Hydroxocobalamin

69%

(24/35)

4

Ibuprofen and acetaminophen

6%

(2/35)

5

MRI

0%

(0/35)

M 6 E

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(M2.PL.14.43) A 30-year-old man is brought to the emergency room by ambulance after being found unconscious in his car parked in his garage with the engine running. His wife arrives and reveals that his past medical history is significant for severe depression treated with fluoxetine. He is now disoriented to person, place, and time. His temperature is 37.8 deg C (100.0 deg F), blood pressure is 100/50 mmHg, heart rate is 100/min, respiratory rate is 10/min, and SaO2 is 100%. On physical exam, there is no evidence of burn wounds. He has moist mucous membranes and no abnormalities on cardiac and pulmonary auscultation. His respirations are slow but spontaneous. His capillary refill time is 4 seconds. He is started on 100% supplemental oxygen by non-rebreather mask. His preliminary laboratory results are as follows:
Arterial blood pH 7.20, PaO2 102 mm Hg, PaCO2 23 mm Hg, HCO3 10 mm Hg, WBC count 9.2/µL, Hb 14 mg/dL, platelets 200,000/µL, sodium 137 mEq/L, potassium 5.0 mEq/L, chloride 96 mEq/L, BUN 28 mg/dL, creatinine 1.0 mg/dL, and glucose 120 mg/dL. Which of the following is the cause of this patient's acid-base abnormality?

QID: 104317
1

Increased anions from toxic ingestion

11%

(10/88)

2

Decreased minute ventilation

6%

(5/88)

3

Decreased oxygen delivery to tissues

66%

(58/88)

4

Increased metabolic rate

2%

(2/88)

5

Decreased ability for the tissues to use oxygen

14%

(12/88)

M 5 E

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