Low-level carbon-monoxide poisoning: inability of neuropsychological testing to identify patients who benefit from hyperbaric oxygen therapy.

Introduction: Although major sequelae of carbon-monoxide (CO) poisoning and its treatment with hyperbaric oxygen (HBO) are well-documented, a syndrome of low-level CO poisoning has received relatively little attention. Subtle symptoms of poor concentration, language difficulty, problems with calculations, and memory loss were noted after an acute exposure of 131 dormitory residents to low levels of CO. The CO Neuropsychological Screening Battery (CONSB), a series of tests reported by others as useful to identify victims of CO poisoning, was performed on a subset of 46 victims. It was hypothesized that their test scores would improve after treatment with HBO.

Methods: Testing was performed both before and after HBO on 35 CO-exposed victims. A control group of 20 students residing on the same college campus, but not involved with the CO incident, also were tested on two separate occasions to assess the ability of the test to identify selectively victims of low-level CO poisoning, as well as to evaluate its validity when administered serially.

Results: Both CO-exposed and control subjects demonstrated significant performance improvement when completing the testing for the second time. In addition, the baseline test scores were not significantly different for either the CO-exposed or the control groups. Nonetheless, all CO-exposed victims reported immediate subjective improvement of their symptoms after HBO therapy.

Conclusion: These observations and a review of the literature suggest that there might exist a syndrome of subtle neurological disturbances in victims of low-level CO poisoning. Whether this is permanent or might regress spontaneously over time is unknown. As a diagnostic adjunct, the CONSB does not appear to be as useful in low-level CO poisoning.