As a working definition, chronic CO poisoning involves an exposure to CO that occurs more than once and lasts longer than 24 hours. Accordingly, acute CO poisoning involves an exposure to CO that occurs only once and lasts no longer than 24 hours.
Exposure usually continues for many days, months, and even years.
The boundary limit between acute and chronic exposure is indistinct. The CO exposure need not produce altered consciousness at any time for this to occur. Clearly, prolonged exposure to this insideous poison, even at what were previously thought to be ultra-low levels, is capable of producing many and varied residual health effects. Furthermore the incidence of such unpleasant and often debilitating effects is far higher than was previously believed by the medical and public health community, and can continue for a very long period of time. It is not believed that this body of work answers all of the questions relevant to chonic CO poisoning, but rather will act to spur others to continue investigations of the problem which will provide a better understanding of what occurs and improve treatment for victims in the future.