Carbon Monoxide



Carboxyhemoglobin, CO, COHb, COH.


To identify the amount of carbon monoxide in the blood related to poisoning, toxicity from smoke inhalation, or exhaust from cars.

Patient Preparation

There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings

Method: Spectrophotometry, co-oximetry.

% Saturation of Hemoglobin
NonsmokersUp to 2%
SmokersUp to 10%
CO levels in smokers may reach levels greater than 20%. Variation is due in part to factors such as cigarette brand, number of cigarettes smoked per day, and the time interval during which multiple cigarettes are smoked. Research as to whether electronic cigarettes (vaping) produce clinically significant levels of CO are conflicting; further study is needed.

Critical Findings and Potential Interventions

CO % of Total HemoglobinSymptoms
10%–30%Disturbance of judgment, headache, dizziness
30%–40%Dizziness, muscle weakness, vision problems, confusion, increased heart rate, increased breathing rate
50%–60%Loss of consciousness, coma
Greater than 60%Death

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.

Women and children may suffer more severe symptoms of carbon monoxide poisoning at lower levels of carbon monoxide than do men because women and children usually have lower RBC counts.

A possible intervention in moderate CO poisoning is the administration of supplemental oxygen given at atmospheric pressure. In severe CO poisoning, hyperbaric oxygen treatments may be used.

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