Prediction of Acute Mountain Sickness by Monitoring Arterial Oxygen Saturation During Ascent

Abstract

Acute mountain sickness (AMS) is a common problem while ascending at high altitude. AMS may progress rapidly to fatal results if the acclimatization process fails or symptoms are neglected and the ascent continues. Extensively reduced arterial oxygen saturation at rest (R-Spo₂) has been proposed as an indicator of inadequate acclimatization and impending AMS. We hypothesized that climbers less likely to develop AMS on further ascent would have higher Spo₂ immediately after exercise (Ex-Spo₂) at high altitudes than their counterparts and that these postexercise measurements would provide additional value for resting measurements to plan safe ascent. The study was conducted during eight expeditions with 83 ascents. We measured R-Spo₂ and Ex-Spo₂ after moderate daily exercise [50 m walking, target heart rate (HR) 150 bpm] at altitudes of 2400 to 5300 m during ascent. The Lake Louise Questionnaire was used in the diagnosis of AMS. Ex-Spo₂ was lower at all altitudes among those climbers suffering from AMS during the expeditions than among those climbers who did not get AMS at any altitude during the expeditions. Reduced R-Spo₂ and Ex-Spo₂ measured at altitudes of 3500 and 4300 m seem to predict impending AMS at altitudes of 4300 m (p < 0.05 and p < 0.01) and 5300 m (both p < 0.01). Elevated resting HR did not predict impending AMS at these altitudes. Better aerobic capacity, younger age, and higher body mass index (BMI) were also associated with AMS (all p < 0.01). In conclusion, those climbers who successfully maintain their oxygen saturation at rest, especially during exercise, most likely do not develop AMS. The results suggest that daily evaluation of Spo₂ during ascent both at rest and during exercise can help to identify a population that does well at altitude.

Vagal activity and oxygen saturation response to hypoxia: Effects of aerobic fitness and rating of hypoxia tolerance

“…Susceptibility to AMS was, in addition to a reduction in SpO 2 , also associated with better aerobic capacity, younger age, and higher body mass index in mountain climbers (Karinen et al, 2010). However, we did not find a significant difference in VO 2 max between HCG and HDG in contrast to Karinen et al (2010). A discrepancy in results may be explained by the difference in study design.…”

“…Based on the previous literature (Burtscher et al, 2004;Rathat et al, 1992) and our findings, we feel that a controlled exposure to simulated altitude equal to ~6200 m for 10 minutes in unacclimatized persons before the travelling to high altitude may serve as the screening measurement to assess an individual's hypoxia tolerance. Susceptibility to AMS was, in addition to a reduction in SpO 2 , also associated with better aerobic capacity, younger age, and higher body mass index in mountain climbers (Karinen et al, 2010). However, we did not find a significant difference in VO 2 max between HCG and HDG in contrast to Karinen et al (2010).…”

“…It has previously been shown that both reduced SpO 2 (Burtscher et al, 2004;Karinen et al, 2010) and a stimulated sympathetic system (Mazzeo et al, 1995) during hypoxia contributes to AMS susceptibility. Our findings demonstrate a significantly greater desaturation level in subjects who rated their 10 minute hypoxia experience as mild or moderately uncomfortable, because of the presence of nausea or vomiting, headache, and weakness, while subjects free of perceived hypoxia-induced side effects demonstrated a significantly lower desaturation together with a lower relative increase in sympathetic activity.…”

“…A discrepancy in results may be explained by the difference in study design. In our study, volunteers were exposed to normobaric hypoxia for 10 minutes during rest, whereas Karinen et al (2010) assessed SpO 2 response in climbers during mountain expeditions.…”

“…Importantly, the SpO 2 response to hypoxia at rest (Burtscher, Flatz, & Faulhaber, 2004) and the combination of rest and exercise (Karinen, Peltonen, Kähönen, & Tikkanen, 2010;Rathat, Richalet, Herry, & Larmignat, 1992) has been suggested by some authors to be a promising marker of susceptibility to acute mountain sickness (AMS) development, while others have reported opposite findings (Wille et al, 2012;O'Connor, Dubowitz, & Bickler, 2004). For example, subjects that manifested AMS symptoms exhibited both a greater decline in SpO 2 in hypoxia and a higher maximal oxygen uptake (VO 2 max) compared with subjects who were free from AMS symptoms (Karinen et al, 2010). Previous research also reported that VO 2 max may have a negative influence on the SpO 2 response to simulated altitude (2500-4600 m) at rest (Woorons et al, 2007) but particularly during moderate exercise intensity.…”