Carboxyhemoglobin (CO-Hb)

What sample is needed 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 for more than 4 months in a well-capped bottle.
3. Blood in EDTA anticoagulant is stable at room temperature for over a week.

What are the precautions for Carboxyhemoglobin?

1. Don’t use oxalate for the blood sample.
2. Collect the blood sample before starting oxygen therapy.
3. O2 saturation and oximetry are inaccurate in CO poisoning because they measure all forms of O2, including O2-saturated hemoglobin and CO-Hb.

What are the 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.

How will you define Carboxyhemoglobin?

1. Carbon monoxide (CO) is colorless, odorless, and tasteless, undetectable unless mixed with a visible or odorous pollutant.
2. The incomplete combustion of fuels such as gasoline produces carboxyhemoglobin (CO-Hb).
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 that produces hypoxic injury due to O₂ deprivation.
5. Cherry-red skin is a good clue for Carbon monoxide poisoning.

What is the mechanism of Carboxyhemoglobin (CO-Hb) poisoning?

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 (200 times more affinity than oxygen).
3. CO-Hb produces a cherry-red or violet color on the skin.

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

10. CO poisoning is directly toxic to the intracellular oxidative mechanism and produces more nitric oxide (NO).
11. When CO poisoning occurs, request a Hb analysis for CO-Hb.
12. CO is readily cleared by breathing normal air.
13. Fetal Hb has more affinity for CO, and if these fetuses are exposed to CO, they are more at risk.

What are the sources of carbon monoxide (CO)?

1. Newborns, where the fetal Hb breakdown yields endogenous CO.
2. Tobacco smoke.
3. Automobile exhaust fumes.
4. Natural gas heaters are used in areas with limited ventilation.
5. Industrial pollution includes:
   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 heme, and the CO-Hb level is ≥1% (0.2% to 0.8%).
   2. It is increased in hemolytic anemia and in smokers.
   3. Bleeding in the intestine.
   4. In smokers, it may vary from 4% to 20%.
   5. In the case of smokers exposed to CO, they may have CO-Hb of around 10%.
   6. CO is also produced in the liver by metabolizing dichloromethane (methyl chloride), which is found in paints and varnishes.
9. People  who are prone to poisoning:
   1. In defective furnaces.
   2. A worker, such as a coal miner.
   3. The firefighter.
   4. Smokers of cigarettes, cigars, or pipes in a closed space.
   5. Accidental poisoning was most often seen in house fires, engine exhaust (such as a car left running in a 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 CO elimination is approximately 4 hours for a person breathing atmospheric air.
    1. But for smokers, this level may remain high.

What are the signs and symptoms of Carbon monoxide (CO) poisoning?

1. The brain and the heart are more susceptible to the effects of CO.
2. Chronic exposure to CO may lead to polycythemia.
3. CO-Hb produces a 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. A carboxyhemoglobin content of 30% to 40% is associated with severe symptoms.
   2. A 50% association is noted with coma.
   3. Cigarette smoking may produce levels as high as 10% to 15%.
6. There is 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.

What are the effects of Carbon monoxide % levels on the body?

What are the various levels of Carboxyhemoglobin (CO-Hb) % and clinical effects on the body?

What symptoms are correlated with % of carbon monoxide (CO) poisoning?

How will you do a 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.

What is the normal level of carboxyhemoglobin (CO-Hb)?

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

Source 3

Saturation of hemoglobin by carbon monoxide (CO)

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

Source 2

What are the clinical values and their effects due to Carboxyhemoglobin?

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%

What is the cause of the increased level of CO?

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

What are the Lab findings in CO poisoning?

1. Whole blood, with heparin or EDTA as the 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. Arterial 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.

How will you treat CO poisoning?

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).

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