Pulse oximetry during severe physical exercise at high altitude

Introduction: During sojourns at high altitude pulse oximetry is widely used to facilitate the diagnosis of high altitude illness at an early state and to assess the individual acclimatization status. With regard to the second topic there is good evidence that measurements during physical exercise have a higher significance compared to measurements at rest. However, physical exercise, especially moving hands may influence the measurements. This raises the question whether body movement compromises the use of pulse oximetry during physical exercise. Objective: To investigate the amount of incorrect measurements during severe physical exercise with extreme manual activity at high altitude. Methods: The used device (PalmSat 2500®; Nonin) records the measured values for Sp02 and pulse every 4 seconds. To minimize interference with the ice axes we placed the flex finger sensor not on the index but on the forth finger. The hands were covered with gloves. The study was performed during an extreme ice-climb to the summit of Les Courtes (3856 m; NE-gully: 800 m; 50°) in two experienced ice-climbers (both 32 yrs., 72/74 kg, non-smoking man). The recorded data were transferred to Excel and evaluated. The PalmSat 2500 assigns the figure "500" to each incorrect (missing or suspect) measurement. This ensures a value every 4 seconds. We calculated the ratio of these "500"-values compared to the total number for the extreme situation during the ice-climb as well as for the whole tour. Results: During the whole tour and during the ice-climb we recorded 2252 data points for Sp[O.sub.2]. In total we had 24.8% (1333/5368) of incorrect measurements and 34.5 (778/2252) for the ice climb. If we exclude the ice-climb the rate of incorrect measurement is 17.8 (555/3116) and if we further exclude the 6 min for preparation immediately before the ice-climb the rate of incorrect measurements is 16.8 (510/3028). Conclusions: Even under these extreme conditions pulse oximetry provides meaningful results. For practical use 2/3 of usable results is sufficient. In situations where considerable hand-movements are unavoidable the use of ear-sensors might reduce the rate of incorrect measurements. Key words: acute mountain sickness, pulse oximetry, oxygen saturation, moving artifact