Discussion

A depletion of cerebral oxygenation in high altitudes is well-known, with a potential adaptation in long-term residents of high-altitude areas. ^{Reference Ze, Liu and Yang Jin15–Reference Furian, Latshang and Aeschbacher17} However, to the authors’ knowledge, this was the first study assessing cerebral oxygenation (and confirming depleted values) at a high altitude in mountain rescuers after a steep active ascent towards a potential patient, and therefore serving as proof-of-concept. The measured rSO2 values roughly reflect known ranges from other high-altitude populations. ^{Reference Furian, Latshang and Aeschbacher17,Reference Hadolt and Litscher18} A high inter-variability of delta rSO2 could be observed when looking at the mountain rescuers’ values individually. This was not directly reflected by the degree of hypoxemia measured by SpO2 (%) which were at levels that are comparable to previous literature. ^{Reference Egger, Niederer and Tscherny13,Reference Wang, Tsai and Chen19,Reference Narahara, Kimura and Suto20} Many confounders that could not be assessed may have played a role. However, it must be remembered that the participants were all relatively young, very fit, and generally healthy. This, and the low degree of subjective and objective physical exhaustion in the study subjects, ^{Reference Egger, Niederer and Tscherny13} make the results even more interesting and lead to additional questions: (1) Are there factors influencing cerebral oxygenation that are independent of physical fitness and mountain experience? And (2) Is individual adaptation of cerebral oxygenation at high altitudes maybe the more promising method of assessing and determining task performance in mountainous settings? These questions are in line with previous findings. For instance, Hadolt, et al also found a more pronounced depletion in cerebral than in peripheral oxygenation in Himalayan trekkers, ^{Reference Hadolt and Litscher18} whereas Manferdelli, et al reported individuals being more prone to AMS when they showed low cerebral oxygenation values both at rest and during exercise. It was suggested that those individuals were unable to increase microvascular blood volume and therefore maintain oxygenation in hypoxic surroundings. ^{Reference Manferdelli, Marzorati, Easton and Porcelli21}

The theory of decreased cognitive function in hypobaric hypoxic conditions is well-established. ^{Reference Furian, Latshang and Aeschbacher17,Reference Wang, Sang and Cui22,Reference Kammerer, Faihs and Hulde23} High-altitude ascents undoubtedly pose a (patho-)physiological cerebrovascular challenge, ^{Reference Lafave, Zouboules and James24} and a reduction of cerebral oxygenation is thought to be the primary cause of AMS. ^{Reference Hadolt and Litscher18,Reference Kammerer, Faihs and Hulde23} It has previously been shown that the physical strain of an alpine ascent potentially leads to a reduction in performance quality performed of mountain rescuers, and that respective guidelines (for instance on cardiopulmonary resuscitation) are thus potentially not a good fit to alpine surroundings. ^{Reference Egger, Niederer and Tscherny13} Performing an active on-foot ascent to get to a patient or victim in alpine surroundings is regularly necessary, as the use of HEMS is not always possible. ^{Reference Egger, Niederer and Tscherny13} Also, individuals transported to high altitudes with a helicopter have previously shown unfavorable neurocognitive ^{Reference Davranche, Casini, Arnal, Rupp, Perrey and Verges25} and practical ^{Reference Wang, Tsai and Chen19} performance, probably due to changes in cerebrovascular reactivity. ^{Reference Liu, Zhang, Luo, Hu, Ma and Wu26} Vuyk, et al reported that Acetazolamide may dampen the exercise-induced depletory effect of high altitudes on cerebral oxygenation. ^{Reference Vuyk, Van Den Bos and Terhell27} Accordingly, Sildenafil is thought to improve rSO2 at altitude. ^{Reference Chan, Hoar and Pattinson28} Whether such pharmacological interventions could be an option to improve performance of mountain rescuers after they had to perform strenuous ascents remains unknown and could be the goal of future research.

Other supportive tools of MRS such as mechanical chest compression devices have already been tested in alpine settings ^{Reference Alexander, Katharina and Verena29} and may be worthwhile to use when optimal human performance cannot be guaranteed because rescuers are simply not oxygenated enough.

Due to rising numbers of complex medical cases in mountainous regions, ^{Reference Martínez-Caballero and Sierra Quintana10–Reference Ströhle, Vögele, Neuhauser, Rauch, Brugger and Paal12} the performance of rescue teams should indeed be moved more into the spotlight of research – cerebral oxygenation and its modulation could play a vital role.