Refer to: Hultgren HN: High altitude medical problems (Medi- Medical Progress cal Progress). West J Med 131:8-23, Jul 1979 High Altitude Medical Problems HERBERT N. HULTGREN, MD, Palo Alto, California Increased travel to high altitude areas by mountaineers and nonclimbing tour- ists has emphasized the clinical problems associated with rapid ascent. Acute mountain sickness affects most sojourners at elevations above 10,000 feet. Symptoms are usually worse on the second or third day after arrival. Gradual ascent, spending one to three days at an intermediate altitude, and the use of acetazolamide (Diamox) will prevent or ameliorate symptoms in most instances. Serious and potentially fatal problems, such as high altitude pulmonary edema or cerebral edema, occur in approximately 0.5 percent to 1.0 percent of visitors to elevations above 10,000 feet-especially with heavy physical exertion on arrival, such as climbing or skiing. Early recognition, high flow oxygen therapy and prompt descent are crucially important in management. Our knowledge of the causes of these and other high altitude problems, such as retinal hemor- rhage, systemic edema and pulmonary hypertension, is still incomplete. Even less is known of the effect of high altitudes on medical conditions common at sea level or on the action of commonly used drugs. EXPOSURE TO HIGH ALTITUDE of people of all hiked up to Pheriche (14,000 feet) en route to the ages and degrees of health has enormously in- Everest base camp. In the Mount Kenya area 3,- creased in the last ten years. Modern travel facili- 500 climbers and trekkers climb above 13,000 ties and the advent of mountain tours and trek- feet each year. Skiers in the Rocky Mountains are king safaris now permit access to high mountain not immune to high altitude illness; many ski re- regions previously visited only rarely by hardy sorts are located at 8,000 feet or higher, with ski climbers. In 1976 there were 671 climbers on runs starting at 11,000 and 12,000 feet. Such re- Mount McKinley (20,320 feet) and each year sorts can be easily reached in one day from any more than 5,000 people climb Mount Rainier part of the United States. High altitude pulmonary (14,408 feet). In the Himalayas during one four- edema has been observed in hikers and skiers in week period in 1975 there was 522 trekkers who the Sierra Nevadas, and helicopters now carry skiers to 12,500 feet from the eastern side of the Dr. Hultgren is Chief, Cardiology Service, Veterans Administra- tion Medical Center, Palo Alto, California; Professor of Medicine, Sierras. In South America large permanent popu- Stanford University School of Medicine, and Chairman, Medical Committee, American Alpine Club, New York City. lations live and work at altitudes as high as 16,- This work was supported by research funds from the Veterans Administration Medical Center, Palo Alto, California. 500 feet. Physicians should be aware of common Reprint requests to: Herbert N. Hultgren, MD, Veterans Ad- medical problems of acute and chronic high alti- ministration Medical Center, 3801 Miranda Avenue, Palo Alto, CA 94304. tude exposure. For these reasons this review of 8 JULY 1979 * 131 * 1 HIGH ALTITUDE MEDICAL PROBLEMS 10r ABBREVIATIONS USED IN TEXT a AMS=acute mountain sickness HAPE=high altitude pulmonary edema z 90F- 0 current concepts of high altitude illness has been D 80 prepared. : cn Definition of High Altitude Z 70 0crui For the purpose of this review high altitude will w o Rest 0L refer to elevations of 8,000 to 15,000 feet above 60_ * Exercise 300 kg-m/min. sea level. It is rare for symptoms of altitude ill- * 900 kg-m/min. ness to occur below 8,000 feet and few mountain ft tours or permanent human habitations extend Sea level 5,400 10,150 14,900 19,000 above 15,000 feet. ALTITUDE (Ft.) Figure 1.-Arterial oxygen saturation in normal man at Role of Hypoxia sea level and various altitudes at rest and during It is apparent that the most moderate exercise. (Reprinted with permission from important effect Banchero et of high altitude exposure is hypoxia. At 12,000 al.1) feet the normal resting arterial oxygen saturation AMS is the most common high altitude illness. is 85 percent. At 15,000 feet the saturation falls Excellent descriptions of AMS have been pub- to 78 percent. At 19,000 feet the arterial satura- lished by Acosta5 and Barcroft.6 Acosta's descrip- tion is 69 percent. During exercise at sea level tion is one of the earliest published records of arterial oxygen saturation does not fall. However, AMS (1589). Barcroft's report describes symp- during exercise at high altitude oxygen saturation toms affecting passengers on a train trip from falls due to limitations in maximal pulmonary Lima to Cerro de Pasco, Peru (14,200 feet). The diffusing capacity (Figure 1). At 15,000 feet the most common initial symptom consists of head- saturation may fall to 69 percent and at 19,000 ache, which may vary in severity from a mild feet heavy exercise may decrease arterial satura- feeling of lightheadedness or dizziness to severe, tion to levels as low as 40 percent to 50 per- prolonged, incapacitating pain. Lassitude, ano- cent.'-3 This is one factor that limits climbing rexia, drowsiness, a general feeling of malaise, performance at very high altitudes. In addition, weakness and dyspnea on exertion are common. during sleep at high altitude the drop in arterial During ascent, somnolence, chilliness with pallor saturation is considerably more than the slight of the face, and cyanosis of the lips and nailbeds decrease observed at sea level. Persons at 17,200 are frequently noted. Nausea and vomiting may feet with an arterial oxygen saturation of 74 occur, especially in children. percent when awake have a mean saturation of After arrival, a feeling of warmth and flushing 64 percent during sleep. With irregular respiration of the face may be noted for the first 24 to 48 during sleep, saturations below 40 percent have hours. The above symptoms may persist for sev- been observed.4 eral days, although in most instances they disap- While arterial carbon dioxide tension (Pco2) pear within 24 to 48 hours. Sleep, especially for falls during high altitude exposure it is unlikely the first few nights, is difficult, with frequent that hypocapnia is responsible for symptoms of periods of wakefulness and often strange dreams. altitude exposure. Even slight physical effort may produce trouble- some dyspnea, often requiring considerable rest Acute Mountain Sickness until the respiratory distress has ceased. Weakness Rapid exposure to high altitude of unacclima- and palpitation on effort may be noted; tachy- tized persons commonly results in a group of cardia may be present. A common complaint is symptoms generally known as acute mountain dull pain and discomfort in the the muscles of the sickness (AMS). Severe symptoms rarely occur posterolateral chest wall. Cheyne-Stokes respira- below 8,000 feet and in most persons some symp- tion may be experienced above 8,000 feet and it toms will be present from 10,000 to 12,000 feet. occurs in nearly all persons at altitudes above THE WESTERN JOURNAL OF MEDICINE 9 HIGH ALTITUDE MEDICAL PROBLEMS 13,000 feet. It appears most frequently during in the relief of symptoms but in facilitating restful the night and is a major factor in preventing sleep. Lightweight oxygen tankws are now available sound, restful sleep. If present during the day, that provide 247 liters of oxygen with a variable it does not appear to be related to activity or flow regulator with a carrying weight of only meals. It is rarely continuous, but appears and 6h pounds (Erie Manufacturing Co., 4000 S. disappears, lasting for minutes to hours. 13th St., Milwaukee, Wisconsin 53221). Neurologic and cerebral symptoms may be Prevention experienced, including a reduced capacity for The most effective method of preventing AMs sustained mental work, memory defects, auditory is by acclimatization. This can be achieved by a. and visual disturbances, vertigo and tinnitus. Ir- sojourn at an intermediate altitude (6,000 to ritability may be noted. Appetite may remain 8,000 feet) for two to four days before going to poor; a weight loss of from 5 to 10 pounds may a higher altitude. Another effective measure is occur in adults. In some persons symptoms may gradual ascent by climbing 1,000 feet per day persist throughout their stay at high altitudes and interrupted by an occasional day of rest. In trek- may result in their inability to work efficiently king parties to the Everest base camp AMS was or, in some cases, may necessitate a return to seen far more frequently in those who flew from sea level. Katmandu to Lukla (9,240 feet) than in those Headache is the most severe and disabling who walked this distance over 13 days.' For those symptom of AMS. It has been suggested that head- persons susceptible to AMS the administration of ache is due to cerebral edema; however, cerebral acetaxolamide (Diamox) may be helpful.74- Ace- edema in other clinical conditions is not regu- tazolamide may be given in a dose of 250 mg once larly assocated with headache. A more plausible or twice a day beginning on the day of ascent cause is spasm or dilatation of cerebral blood and continued for two to five days after arrival. vessels related to hypocapnia (which causes cere- Side effects such as tingling of the lips and finger bral vasoconstriction) or hypoxia (which causes tips, alteration in the taste of beer and myopia cerebral vasodilatation). usually occur only if acetazolamide administra- AMS may not be evident during the first 24 tion is continued for more than five days.7'8 Field hours of altitude exposure and the symptoms are studies of troops have shown that AMS at 14,200 usually most severe on the second and third day.