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Introduction ⬇

Carboxyhemoglobin is formed when Hb is exposed to carbon monoxide (CO). The affinity of Hb for CO is 240 times greater than for oxygen. CO poisoning causes anoxia because the carboxyhemoglobin formed does not permit Hb to combine with oxygen.

This test is done to detect CO poisoning. Because carboxyhemoglobin is not capable of transporting oxygen, hypoxia results, causing headache, nausea, vomiting, vertigo, collapse, or convulsions. Death may result from anoxia and irreversible tissue changes. Carboxyhemoglobin produces a cherry red or violet color of the blood and skin, but this may not be present in chronic exposure. The most common causes of CO toxicity are automobile exhaust fumes, coal gas, water gas, and smoke inhalation from fires. Smoking is a minor cause.

Normal Findings ⬆ ⬇

Nonsmokers: <2.0% of total Hb or <0.02 fraction of Hb saturation

Heavy smokers: 6.0%–8.0% or 0.06–0.08 fraction of Hb saturation

Light smokers: 4.0%–5.0% or 0.04–0.05 fraction of Hb saturation

Newborns: 10%–12% or 0.10–0.12 fraction of Hb saturation

Clinical Alert

  1. With values of 10%–20% (0.10–0.20), the patient may be with no symptoms.

  2. With 20%–30% (0.20–0.30), headache, nausea, vomiting, and loss of judgment occur.

  3. With 30%–40% (0.30–0.40), tachycardia, hyperpnea, hypotension, and confusion occur.

  4. With 50%–60% (0.50–0.60), there is loss of consciousness.

  5. Values of >60% (>0.60) cause convulsions, respiratory arrest, and death.

Procedure ⬆ ⬇

  1. Obtain 5 mL of a venous blood sample using a green-topped tube (with EDTA). Label the specimen with the patient’s name, date and time of collection, and test(s) ordered.

  2. Keep the sample tightly capped and transport to the laboratory immediately in a biohazard bag.

Clinical Implications ⬆ ⬇

  1. Carboxyhemoglobin is increased in:

    1. CO poisoning from many sources, including smoking, exhaust fumes, fires

    2. Hemolytic disease

    3. Blood in intestines

    4. Newborns because of Hb F breakdown that yields endogenous CO

  2. A direct correlation has been found between CO and symptoms of heart disease, angina, and MI.

Interventions ⬆

Pretest Patient Care

  1. Advise patient of purpose of test.

  2. Draw blood sample before oxygen therapy has started.

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Explain the causes of headache, dizziness, vomiting, convulsions, or coma.

  2. Treatment consists of removal of the patient from the source of CO.

  3. Initiate oxygen therapy either by supplemental oxygen at atmospheric pressure or by hyperbaric oxygen.

  4. Possible treatments include administering high concentrations of O2 under hyperbaric conditions as ordered.

  5. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.