High Altitude Medicine: Impacts for Anesthesia?

Abstract

Until recently altitudes above 4000 m were mostly visited by trained and experienced mountaineers, today these altitudes are open to anybody thanks to increased wealth, leisure time and mobility as well as to commercial trekking and mountaineering agencies. Therefore, practitioners are increasingly confronted with questions concerning high altitude tolerance. Often such questions are asked by individuals that have no prior mountaineering experience, have never been to high altitudes and may even be under treatment for chronic diseases. Therefore, knowledge about the physiology of acclimatization to high altitude, about high altitude illnesses as well as high altitude tolerance of patients with cardio-pulmonary disease is particularly important for those doctors who are asked for advice by people who intend to go to high altitude as well as for those doctors who accompany trekkings or expeditions. This mini-symposium demonstrates that we have quite a good knowledge, based on scientific data, about the physiology of acclimatization to hypoxia, while our understanding of the pathophysiology of high altitude illnesses is still rather speculative, although considerable progress has been achieved recently regarding the pathogenesis of high altitude pulmonary edema. Unfortunately, there are almost no controlled studies that investigate possibilities of assessment of tolerance to high altitude in healthy individuals or patients. Is research in high altitude medicine of any relevance for anesthesiology or intensive care medicine? At first glance there appears to be a big contrast : In anesthesia and intensive care medicine one tries with all means of the art to avoid blood gases, to which mountaineers or trekkers expose themselves voluntarily. A mountaineer who ascends rapidly to the Margherita Hut (4559 m) will have an arterial PO2 of about 40 mmHg and an arterial oxygen saturation between 70 and 80 % on the day of arrival. Except for a reduced performance, this level of hypoxemia does not have negative effects regarding well-being and health in those 50 % of the mountaineers who can tolerate such a rapid exposure without developing acute mountain sickness or high altitude pulmonary edema [1]. Equally impressive is the potential of adaptation of healthy humans to hypoxia. A pilot candidate of the Air Force who has to participate in an educational „demonstration on the effects of lack of oxygen” during which he is exposed rapidly to a simulated altitude of 8800 m will pass out within 10-15 minutes, if the doctor running the experiment does not give him the oxygen mask in time [2]. On the contrary, a mountaineer who ascends slowly over 6-8 weeks to the same altitude on Mount Everest is able to perform about 100 Watt at this altitude and will tolerate the following arterial blood gases : PO2 = 28 mmHg, PCO2 = 10 mmHg and SaO2 = 50 %, pH = 7,52 (at rest 7,56) [3]. Even during such maximal exercise in extreme hypoxia, one does not find arrhythmias or sign or ischemia in the ECG [4], while subtle cerebral dysfunctions occur (in most cases transiently) in some individuals [5]. The discrepancy between high altitude medicine and anesthesia will disappear when looking at it from a different point of view. The blood gas values reported from high altitude show which degree of hypoxemia can be tolerated without apparent damage by healthy individuals during acute and chronic exposure to hypoxia. Perhaps, one should keep in mind these blood gas values of healthy individuals at altitudes of 4500 m when balancing over the narrow ridge between oxygen toxicity and hypoxemia in anesthesiology and intensive care medicine.