Carbon monoxide exposure on Denali: comparing the 2004 and 2005 climbing seasons

This study assessed a potential relationship between elevated carboxyhemoglobin (COHb) levels and the presence of acute mountain sickness (AMS) at 4300 m on Denali and evaluated the relationship between COHb levels, AMS, and climber characteristics and behaviors. Building on our research done in 2004, in this article we report further data gathered during the 2005 climbing season and evaluate the combined results.

Participants were screened for AMS using the Lake Louise Self-Report Questionnaire and answered questions focusing on AMS symptoms, AMS prevention, and previous history of altitude illness. Carboxyhemoglobin levels were measured by serum co-oximetry. Additional questions assessed stove practices, climbing practices, and climber behaviors. Nonparametric statistical analyses were performed to examine potential relationships between COHb levels, AMS symptoms, and climber behaviors across the 2 years and with years combined.

Overall, 317 climbers participated in the 2-year study. As in 2004, the combined data demonstrated no relationship between positive carbon monoxide (CO) exposure and positive criteria for AMS (P = .276). Climbers in 2005 were 1.92 times more likely to meet positive criteria for AMS, compared to climbers in 2004 (P = .028). On the contrary, climbers in 2004 were 3.93 times more likely to be CO exposed than climbers in 2005 (P = .003). Overall, climbers descending the mountain were more likely to be positive for CO exposure (5.56 times more likely than ascending climbers, P = .002) and to have higher overall mean COHb levels (2.26% descending vs 0.93% ascending, P = .006). The previous association between increased stove use and climbers who met positive criteria for AMS was not observed in the 2005 or in the combined data (P = .715). A relationship was observed between increased hours of operating stoves and increased COHb levels (P = .002). Female climbers were 2.041 times more likely to meet criteria for AMS (P = .043).

No relationship between AMS symptoms and CO exposure was observed. As found in our initial study, descending climbers had higher overall COHb levels and an increased risk of CO exposure (COHb of >3% in nonsmokers and >10% in smokers). Also, increased hours of stove operation was linked to climbers who had elevated COHb levels.