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Carboxyhemoglobin (CO-Hb), Carbon Monoxide (CO) Poisoning

August 20, 2023Chemical pathologyLab Tests

Table of Contents

Toggle
  • Carboxyhemoglobin (CO-Hb)
      • Sample for Carboxyhemoglobin (CO-Hb)
      • Precautions for Carboxyhemoglobin
        • Purpose of the test (Indications) for Carboxyhemoglobin (CO-Hb)
      • Pathophysiology of Carboxyhemoglobin (CO-Hb)
        • Definition of Carboxyhemoglobin:
      • Carboxyhemoglobin (CO-Hb) Poisoning mechanism:
      • Sources of carbon monoxide (CO) are:
      • Signs and symptoms of Carbon monoxide (CO) poisoning:
        • Symptoms are correlated with % of carbon monoxide (CO) poisoning:
      • Measurement (Lab diagnosis) of CO poisoning:
      • The normal level of carboxyhemoglobin
        • Source 3
        • Source 2
        • Source 4
      • Increased level of CO:
      • Lab findings in CO- poisoning:
      • Treatment:
      • Questions and answers:

Carboxyhemoglobin (CO-Hb)

Sample for Carboxyhemoglobin (CO-Hb)

  1. Collect the venous blood immediately when CO poisoning is suspected.
    1. Heparinized arterial or venous blood for spectrophotometric methodology.
    2. Because CO is rapidly cleared from the hemoglobin when the patient is exposed to fresh air.
  2. Whole blood in heparin is stable >4 months infilled well-caped bottle.
  3. Blood in EDTA anticoagulant is stable at room temperature for over a week.

Precautions for Carboxyhemoglobin

  1. Don’t use oxalate for the blood sample.
  2. Collect the blood sample before oxygen therapy is started.
  3. O2 saturation and oximetry are inaccurate in the CO-poisoning because it measures all forms of O2 – saturated hemoglobin and CO-Hb.

Purpose of the test (Indications) for Carboxyhemoglobin (CO-Hb)

  1. This test is done to detect carbon monoxide poisoning.
  2. It is prescribed for patients who are exposed to smoke inhalation, exhaust fumes, and fires.

Pathophysiology of Carboxyhemoglobin (CO-Hb)

Definition of Carboxyhemoglobin:

  1. Carbon monoxide (CO) is colorless, odorless, and tasteless, undetectable unless mixed with a visible or odorous pollutant.
  2. Carboxyhemoglobin (CO-Hb) is produced by the incomplete combustion of fuels such as gasoline.
  3. Carbon monoxide (CO) binds more tightly with hemoglobin than O2. It displaces the O2 and causes hypoxia.
  4. Carbon monoxide (CO) is a chemical agent which produces hypoxic injury due to O2 deprivation.
  5. There is Cherry red skin is a good clue for Carbon monoxide poisoning.

Carboxyhemoglobin (CO-Hb) Poisoning mechanism:

  1. Carbon monoxide (CO) is produced in the environment where there is partial combustion of Carbon-containing fossil fuels.
    1. Complete oxidation leads to the production of CO2.
  2. Carbon monoxide (CO) combines with hemoglobin with 200 times more affinity than oxygen.
    1. CO + Hb = CO-Hb
  3. CO-Hb produces a cherry-red or violet color on the skin.
Carbon monoxide (CO) poisoning

Carbon monoxide (CO) poisoning

  1. So in the presence of CO, few sites are available for O2 to combine with Hb.
  2. Less O2 is available for tissue respiration leads to Hypoxemia because CO-Hb cannot transport O2.
  3. CO has a high affinity for hemoglobin, almost 210 times that of oxygen.
  4. CO will combine with the hemoglobin and form carboxyhemoglobin (CO-Hb).
  5. Normally carboxyhemoglobin (CO-Hb) is a small fraction of the total hemoglobin <0.5%.
  6. CO-Hb at a higher level leads to toxic symptoms.
Carboxyhemoglobin (CO-Hb): CO-Hb sites for O2 leading to hypoxemia

Carboxyhemoglobin (CO-Hb): CO-Hb sites for O2 leading to hypoxemia

  1. CO poisoning is directly toxic to the intracellular oxidative mechanism and produces more nitric oxide (NO).
  2. When CO poisoning takes place, ask for Hb analysis for CO-Hb.
  3. CO is readily cleared by breathing normal air.
  4. Fetal Hb has more affinity for CO, and if these fetuses are exposed to CO, they are more at risk.

Sources of carbon monoxide (CO) are:

  1. Newborn where the fetal Hb breakdown yields endogenous CO.
  2. Tobacco smoke.
  3. Automobile exhaust fumes.
  4. Natural gas heaters where there is less ventilation.
  5. Industrial pollution like:
    1. Coal gas.
    2. Charcoal burning.
    3. Tobacco smoke.
  6. Defective gas stoves.
  7. Petroleum and natural gas fuel fumes.
  8. Endogenous production of the CO:
    1. It is produced from the heme, and the CO-Hb level is ≥1% ( 0.2% to 0.8%).
    2. It is increased in hemolytic anemia and smokers.
    3. Bleeding in the intestine.
    4. In smokers, it may vary from 4% to 20%.
      1. In the case of smokers exposed to CO may have CO-Hb of around 10%.
    5. CO is also produced in the liver by metabolizing dichloromethane (methyl chloride), which is found in paints and varnish.
  9. People  who are prone to get CO-poisoning:
    1. In defective furnaces.
    2. A worker such as a coal miner.
    3. The firefighter.
    4. Smokers of cigarettes, cigars, or pipes in the closed space.
    5. Accidental poisoning was most often seen in house fires, engine exhaust (car left starting in the closed garage), indoor heaters, and stoves.
    6. Unventilated spaces where charcoal and gas are burning are the source of poisoning during winter power outages.
  10. Intentional CO poisoning is common in suicide cases.
  11. The half-life of elimination of CO is about 4 hours for a person breathing atmospheric air.
    1. But for smokers, this level may remain high.

Signs and symptoms of Carbon monoxide (CO) poisoning:

  1. The brain and the heart are more prone to be affected by CO.
  2. Chronic exposure to CO may lead to polycythemia.
  3. CO-Hb produces cherry-red color on the blood and skin.
  4. There is a direct relationship between CO and heart disease, angina, and myocardial infarction symptoms.
  5. This CO poisoning occurs from house fires, gas heaters, stoves, and engine exhausts.
    1. 30% to 40% of carboxyhemoglobin contents are associated with severe symptoms.
    2. >50% is associated with coma.
    3. Cigarette smoking may produce levels as high as 10% to 15%.
  6. There are nausea and weakness.
  7. There is a headache, dizziness, and vomiting.
  8. Tinnitus is ringing in the ears.
  9. It upsets the stomach.
  10. The patient may have chest pain.
  11. The patient will be confused.
  12. Drunk or sleeping people may die due to CO poisoning.

Carbon monoxide % level effects on the body:

Carbon monoxide (CO) level Clinical presentation of the patient
  • 0.4% to 2%
  • Normal (nonsmoker person)
  • 2% to 6%
  • Normal smoker
  • 10% to 20%
  1. Headache
  2. Dyspnea on exertion
  3. Mild symptoms
  • 20% to 50%
  1. Severe symptoms
  2. Lethargy
  3. Headache
  4. Loss of consciousness
  • >50%
  1. The patient will go into a coma
  2. Ultimately there is death

Various levels of Carboxyhemoglobin (CO-Hb) % and clinical effects on the body:

Carboxyhemoglobin (CO-Hb)-Saturated Hb % Signs and Symptoms
  • 10
  • Slight dyspnoea
  • 20
  • A headache
  • 30
  • Irritable, impaired judgment, Loss of memory
  • 40
  1. Confusion
  2. Decreased vision
  3. Weakness
  • 50
  1. Fainting
  2. Ataxia
  3. Collapse
  • 60
  • Coma
  • > 60    (>70%)
  • Death

Symptoms are correlated with % of carbon monoxide (CO) poisoning:

Carbon-monoxide % Clinical presentation
  • 0% to 2%
  • Patients are asymptomatic
  • 2% to 5%
  1. It is seen in moderate smokers
  2. Patients are usually symptomatic
  3. There may be effects on the orientation
  • 5% to 10%
  1. It is seen in heavy smokers
  2. There is slight dyspnoea on mild exertion
  • 10% to 20%
  1. There is a mild headache
  2. There is moderate dyspnoea on moderate exertion
  • 20% to 30%
  1. There is a marked headache
  2. The Patient is irritable
  3. There is easy fatigability
  4. There is disturbing memory
  5. There is an impairment in the judgment and vision
  • 30% to 40%
  1. There is a severe headache
  2. The patient is confused and dizzy
  3. The patient has weakness and nausea
  4. There is decreased vision
  • 40% to 50%
  1. There is a severe headache
  2. The patient is confused and fainted
  3. The patient may have hyperventilation
  4. Ultimately patient may collapse
  5. There is ataxia
  • 50% to 60%
  1. The patient will go into a coma
  2. The patient will have intermittent convulsions
  • >60%
  1. There is hypotension
  2. Respiratory failure
  3. Death will occur if the exposure to CO is continued
  • 80%
  1. It is a rapidly fatal state
  2. End is death
  3. Death may occur even at a low level of 20%

Measurement (Lab diagnosis) of CO poisoning:

  1. For CO estimation, we can use venous or arterial blood.
  2. CO-oximeter measures CO.
  3. A blood gas analyzer measures oxyhemoglobin by calculation.
  4. Lactate can be measured.
  5. Calculation of the anion gap.
  6. Check myocardial markers.

The normal level of carboxyhemoglobin

Source 1

  • CO-Hb = <0.5% of total hemoglobin.
  • Newborn = up to 5 % saturation of total Hb.
  • Nonsmoker = <3 % saturation of total Hb.
    • Smoker Light = 2% to 5 % saturation of total Hb.
    • Smoker heavy = 5% to 10 % saturation of total Hb.
  • Critical value = >20 % saturation of total Hb.
  • Lethal value   =  >50 % saturation of Hb.

Source 2

Clinical condition % saturation of Hb
  • Nonsmokers
  • 0.5 to 1.5
Smokers
  • 1 to 2 packs /day
  • 4 to 5
  • >2 packs/day  (heavy smoker)
  • 8 to 9
Toxic level
  • Toxic level
  • >20
  • Lethal level
  • >50

Source 3

Saturation of hemoglobin by carbon monoxide (CO)

  • Nonsmoker = <3%
  • Smoker = ≤ 12%
  • Newborn = ≥ 12%

Source 2

Clinical values and their effects:

CO-Hb % Clinical signs and symptoms
  • 20% to 30%
  1. Dizziness
  2. Headache
  3. Disturbance in judgment
  • 30% to 40%
  1. Tachycardia
  2. Hyperpnea
  3. Hypotension
  4. Confusion
  • 50%  to 60%
  • Coma
  • >60%
  • Death

Source 4

  • Nonsmoker = <2% of total Hb.
  • Light smoker = 4 to 5% of total Hb.
  • Heavy smoker = 6 to 8% of total Hb.
  • Newborn = 10 to 12% of the total Hb.

Another source

  • Smoker = 2.1% to 4.2%
  • Nonsmoker = <2.3%

Increased level of CO:

  • This is 50% to 60% seen in CO poisoning.

Lab findings in CO- poisoning:

  1. Whole blood with heparin or EDTA as an anticoagulant is used.
    1. The specimen should be mixed thoroughly before performing the test.
  2. Blood pH is decreased, leading to metabolic acidosis due to tissue hypoxia.
  3. Arteria Oxygen (pO2) is normal. Oxygen (O) is markedly decreased.
  4. Arterial pCO2 may be normal or slightly decreased.
  5. Confirm the carbon monoxide (CO) in the exhaled breath.

Treatment:

  1. CO- toxicity needs a high concentration of O2 to replace the CO-Hb.
  2. In the case of severe CO, toxicity may be treated with hyperbaric oxygen (100% O2 gas).

Questions and answers:

Question 1: What is the fatal level of CO-Hb?
Show answer
>60% level of CO-Hb leads to death.
Question 2: What is the affinity of the hemoglobin with Carbon monoxide (CO)?
Show answer
Carbon monoxide (CO) has 200 times more affinity to bind with the hemoglobin than Oxygen.

Possible References Used
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