Prospective study of accidental carbon monoxide poisoning in 38 Swiss soldiers.

BACKGROUND

Carbon monoxide (CO) poisoning is associated with a wide range of non-specific symptoms, whose time course and prognostic significance are ill defined.

METHODS

We observed a large CO poisoning in a homogenous cohort of 38 male recruits and compared their symptoms with those of 46 unexposed controls from the same military unit. Incident and prevalent symptoms were assessed by sequential questionnaires.

FINDINGS: Carboxyhaemoglobin (COHb) concentration extrapolated to the time of rescue was 30.4 +/- 6.1%. Six recruits were initially unconscious, and five others were unable to get out of their sleeping bags without help. Dizziness was the most common symptom within the first two weeks and was reported in 92% of cases and 13% of controls, followed by headache (87% and 39%) and weakness (76% and 26%). Most symptoms were already present in the first hour, but vomiting, chest pain, and hearing disorders typically had a delayed onset. Headaches, cognitive impairment, and impaired vision were the slowest to resolve. After an initial maximum of 5.6 +/- 2.9 symptoms (p <0.0001 for the comparison with controls), cases reported 5.2 +/- 2.5 symptoms at two days, 1.9 +/- 2.3 symptoms at two weeks, and 1.3 +/-1.6 symptoms at one year (p <0.0001 for decrease over time). Initial palpitations (p = 0.002) and visual changes (p = 0.0003) were independent predictors of a higher symptom score at one year.

INTERPRETATION: In acute CO poisoning there are immediate and delayed symptoms suggesting different pathogenic mechanisms. Visual changes and palpitations are independent predictors of residual symptoms at one year.