Importance of Carboxyhemoglobin in Madison CO Poisoning

The Madison, WI wedding reception that was evacuated due to carbon monoxide resulted in more than two dozen people taken to the hospital. A Metro bus provided a medical staging area for the many guests that were feeling sick. One person fainted due to a generator powering the band that released the toxic gas. It would be important to take the levels of carboxyhemoglobin in the patients.

Carboxyhemoglobin (COHb) occurs when carbon monoxide binds to hemoglobin upon contact in the red blood cells. Even small amounts of carbon monoxide can raise the carboxyhemoglobin level, because carbon monoxide binds to hemoglobin with about 200 times greater affinity than oxygen.

Hyperbaric oxygen treatment is more effective in reducing the half life of COHb than normal oxygen. This line of treatment is recommended for people with high levels of COHb or more severe poisoning, according to an article comparing less severe and more severe carbon monoxide poisoning. A survey indicated that nearly all treatment centers would provide hyperbaric oxygen to people with a COHb level higher than 40 percent.

Fainting can occur with COHb levels of one to three percent. Low carbon monoxide levels can cause chest pain, lack of blood flow and oxygen to the heart muscle, abnormal heart rhythm, congestive heart failure, and death.

Carboxyhemoglobin levels of two to five percent impair visual thresholds, driving skills, and auditory discrimination. Carboxyhemoglobin levels of as low as 4.4 percent reduce work capacity.

Impairments developed with low levels of carbon monoxide include cognitive impairments, such as impaired memory, slow mental processing speed, and executive dysfunction.

Measurement of carboxyhemoglobin levels can determine the severity of carbon monoxide poisoning. COHb levels of less than 10 percent signifies less severe poisoning in one study, but this measure can vary from study to study. Generally, levels less than 15 percent constitutes less severe poisoning.

The study found that CO-related cognitive sequelae, depression, and anxiety are common and may be independent of severity.

As time passes, carboxyhemoglobin levels can decrease. When doing clinical assessment, it is important to consider the length of time that has passed since the poisoning. A study comparing hyperbaric to normobaric oxygen included people with elevated carboxyhemoglobin levels or if they were obviously exposed to CO with it being the only explanation. Some patients with levels lower than ten percent were included because of the time that had passed and that their symptoms could only be explained by CO poisoning.

Carboxyhemoglobin has a half life of four to six hours. It may be considerably shorter than that in children and much shorter when people are given oxygen.

COHb also increases the chances for blood clots. Hyperbaric oxygen is the most effective solution to lowering these levels in the blood and reduce the risk factor for delayed symptoms.