Updated: 6/11/2019

Carbon Monoxide Poisoning

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Questions
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Evidence
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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 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
        • persistent altered mental status despite 100% oxygen administration
        • pregnant women
        • children
        • methylene chloride as cause of CO poisoning
Complications
  • Myocarditis
  • Acute respiratory distress syndrome
 

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Questions (5)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
Calculator

(M2.PL.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? Review Topic

QID: 104772
1

100% oxygen

4%

(1/26)

2

CT

0%

(0/26)

3

Hydroxocobalamin

92%

(24/26)

4

Ibuprofen and acetaminophen

0%

(0/26)

5

MRI

0%

(0/26)

M2

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(M2.PL.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? Review Topic

QID: 109311
1

Methylene blue

0%

(0/25)

2

Hyperbaric oxygen

28%

(7/25)

3

Intravenous epinephrine

4%

(1/25)

4

Sodium thiosulfate and sodium nitrite

4%

(1/25)

5

100% oxygen, hydroxycobalamin, and sodium thiosulfate

64%

(16/25)

M2

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PREFERRED RESPONSE 5

(M2.PL.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? Review Topic

QID: 104317
1

Increased anions from toxic ingestion

8%

(6/80)

2

Decreased minute ventilation

6%

(5/80)

3

Decreased oxygen delivery to tissues

69%

(55/80)

4

Increased metabolic rate

2%

(2/80)

5

Decreased ability for the tissues to use oxygen

14%

(11/80)

M2

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PREFERRED RESPONSE 3
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