Chronic Carbon Monoxide Poisoning usually involves lower levels of the gas in the air and lower blood CO (COHb) concentrations. Exposure usually continues for many days to months. The boundary limit between acute and chronic exposure is indistinct.
The word chronic should be reserved to describe the type of exposure, not the subsequent condition or effect! A damaging effect of CO poisoning, or in fact, any change which persists, should be referred to as a residual effect.
Chronic CO poisoning may not elicit the typical symptoms of (acute) CO poisoning such as headache, nausea, weakness, dizziness, etc. Mucous membranes of the body will almost never be cherry pink. Chronic CO poisoning is often misdiagnosed as chronic fatigue syndrome, a viral or bacterial pulmonary or gastrointestinal infection, a "run-down" condition, immune deficiency, etc. Patients may occasionally present with polycythemia, increased hematocrit, etc.
Chronic CO poisoning is, in fact, difficult to diagnose by those not skilled in its presentation. As stated above, it is often mistaken for chronic fatigue syndrome, viral or bacterial pulmonary or gastrointestinal infection, excessive heat, etc. Similar symptoms seen simultaneously in more than one person, and which disappear upon removal from an environment are tip-offs that CO is involved. COHb is usually not excessively elevated. More often than not, by the time air CO or blood CO levels are measured, the presence of CO in the environment has been corrected, making measurement impossible. Computed tomography (CT) and magnetic resonance imaging (MRI) generally show no lesion, even when psychological/psychiatric and neurologic evaluations may detect functional deficits.
Acute CO Poisoning - Exposure to CO occurs only once and lasts no longer than 24 hours