CARBOXYHEMOGLOBIN. HOW TO AVOID UNDERESTIMATING COHb LEVELs

    The COHb levels should also take into account the delay in sampling after removal from exposure. The half-life of COHb is 4 hours during air breathing (Douglas et al. 1912) and most patients will not have received supplemental oxygen between removal from exposure and blood sampling. A nomogram (see Figure), based on the admission COHb concentration and the time after removal from exposure, is used to obtain an approximate indication of the COHb value at exposure. By using this information, an underestimate of the level of exposure in individual patients can be avoided; and therefore where the patient has been transferred, for instance from a district general hospital to the Regional Burns Unit, with some inevitable delay in sampling, a meaningful value for COHb can be obtained. The value for COHb in the blood has also been found to be useful in identifying patients who are likely to to need intensive therapy. Thus COHb estimation may help to select high-risk patients for elective early transfer to intensive care units, although the numbers of patients studied so far are too small to allow definitive conclusions.

Source: C J Clark. Measurement of toxic combustion productsin fire survivors