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High Yield Topics

High-Altitude Illness

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Ovid: 5-Minute Sports Medicine Consult, The


High-Altitude Illness
Arthur Islas
Basics
  • Altitude illness is a spectrum of symptoms ranging from nausea and headache to pulmonary edema, cerebral edema, and potentially death, due to change in altitude:
    • High altitude: 1,500–3,500 m
    • Very high altitude: 3,500–5,500 m
    • Extreme altitude: Above 5,500 m
  • Altitude illness can be seen at any of these levels, precipitated not only by the altitude achieved, but by a rapid change in altitude. Generally, prevention consists of slow ascent to altitude. Treatment may include medications such as acetazolamide, and always consists of descent to a lower altitude.
  • Sports issues to consider:
    • Train low: Lower-altitude training is optimally below 1,500 m; allows for achievement of high VO2 max, absolute workload, heart rate, and blood lactate concentration.
    • Live (sleep) high: Optimally at an altitude of 2,500–3,000 m will maximize the acclimatization response. The acclimatization response is in part due to increased erythropoietin production, which may require increased iron stores or supplementation:
      • Sea level performance can be enhanced by the physiological effects of acclimatization to altitude. The acclimatization process causes an increase in red cell mass (due to increased erythropoietin production) and accordingly increases the oxygen-carrying capacity of blood, resulting in increases in aerobic power and exercise performance at sea level.
      • There is a further increase in capillary density and ratio of mitochondrial volume to contractile protein.
      • Tissue myoglobin concentration and 2,3-diphosphoglyceric acid increase, which results in increased oxygen uptake of exercising muscle
  • Competition at altitude:
    • VO2 max will decrease at altitude.
    • Acclimatizing at altitude adequately for 1–2 wks can maximize aerobic performance.
    • Improved performance at high altitude is dependent on the athlete's acclimatization, altitude of residence, and the type of athletic event participated in.
    • Athletes in highly anaerobic events such as power lifting or throwing events do not benefit from acclimatization and require only event time arrival.
Description
  • Clinical spectrum of signs and symptoms resulting from ascent to high altitudes are due to hypobaric hypoxia.
  • Hypobaric hypoxia is the physiologic basis for the major altitude illnesses; acute mountain sickness (AMS), high-altitude pulmonary edema (HAPE), and high-altitude cerebral edema (HACE).
  • These high-altitude illnesses frequently overlap in presentation.
  • AMS and HACE are considered as a continuum from mild AMS to HACE.
  • Each syndrome can present independently and progress rapidly, with or without the initial warning of milder symptoms.
  • Untreated HAPE or HACE may end in death.
Epidemiology
  • As many as 38% of unacclimatized individuals may experience symptoms of AMS.
  • The largest study on children and high altitude showed no difference in incidence when compared to adults, though a much smaller study showed that children 6–48 mos had a higher incidence of AMS.
  • Incidence and severity increase with higher altitude and speed of ascent.
Risk Factors
  • Rapid ascent
  • Sleeping at altitude (typically >3,000 ft/night (>1,000 m/night))
  • Inadequate acclimatization
  • Strenuous exertion upon arrival to high altitude
  • Previous history and/or individual susceptibility to altitude illness
  • Low altitude of residence
  • Obesity
  • Chronic illness such as moderate to severe chronic obstructive pulmonary disease, sickle cell disease, uncompensated congestive heart failure, or pulmonary hypertension
  • Well-controlled hypertension and asthma are not considered risk factors.
  • Physically fit individuals have shown a predilection toward altitude illness because of a tendency to exert themselves more upon arrival at altitude and a faster rate of ascent. Physical fitness can be advantageous in performing at altitude when altitude illness is not present, but does not prevent altitude illness.
General Prevention
  • Graded ascent is the best way to prevent high altitude illnesses.
  • Avoid sleeping at altitudes >3,000 m.
  • Spend 2–3 nights at 2,500–3,000 m before going higher.
  • Spend an extra night of acclimatization for every 600–900 m above 3,000 m planned.
  • Avoid 600-m increases in sleeping altitudes above the 2,500-m mark.
Etiology
  • Hypobaric hypoxia:
    • Describes the decrease in the barometric pressure as altitude is gained. This decrease in atmospheric pressure also decreases the partial pressure of oxygen, though the percentage of oxygen in the atmosphere remains stable. This decrease in the partial pressure of oxygen is what precipitates the hypoxia at altitudes, as there is not as much pressure in the atmosphere to drive oxygen into the alveoli and consequently the bloodstream.
    • As altitude is gained and the partial pressure of oxygen is decreased, some very unique physiological responses occur. The carotid body senses the decrease in the partial pressure of oxygen and compensates for this by signalling the respiratory centers in the medulla to increase ventilation. This hypoxic ventilatory response (HVR) is commonly seen, but the extent of the response is genetically determined. This increase in ventilation causes hypocapnia and an alkalosis, which is compensated for by an increase in the excretion of bicarbonate by the kidneys.
    • The HVR also causes hyperpnea resulting in respiratory alkalosis. The central respiratory center responds with periods of apnea, called Cheyne-Stokes breathing, and is one of the factors causing disturbed sleep.
  • HACE:
    • Vasogenic cerebral edema, caused by a myriad of responses to hypobaric hypoxia, including endothelial activation and sympathetic activity.
  • HAPE:
    • A response to hypoxia through multiple mechanisms, which may include microemboli, sympathetic discharge, pulmonary and peripheral vasoconstriction, which all in turn cause increased capillary pressure, which leads to capillary leakage and then to pulmonary edema.
Diagnosis
  • AMS: Any symptom of AMS at altitude should be considered due to altitude until proven otherwise:
    • Headache
    • Insomnia
    • Nausea
    • Anorexia
    • Lassitude
    • Fatigue
    • Weakness
    • Malaise
    • Dizziness
    • Lightheadedness
    • Memory impairment
    • Concentration difficulties
  • HAPE: Half of HAPE victims experience symptoms of AMS in addition to severe dyspnea on exertion progressing to dyspnea at rest:
    • Nonproductive and persistent cough
    • Chest tightness
    • Fatigue
    • Weakness
  • HACE: Ataxia and confusion are widely accepted as the symptoms that signal the progression from AMS to HACE:
    • Headache
    • Lethargy
    • Incoordination
    • Vomiting
    • Disorientation
    • Irrational behavior
    • Visual or auditory hallucinations
    • Seizures
    • Semicoma
    • Unconsciousness (coma may ensue in as little as 24 hr after the onset of ataxia)
History
  • Altitude syndromes:
    • The more rapid the ascent and the higher the altitude attained, the more prevalent and severe the altitude illnesses in those susceptible.
  • AMS:
    • Ascent to high altitude with onset of symptoms in 12–24 hr (symptoms can start as soon as 2 hr after arrival but rarely after 36 hr)
  • HAPE:
    • Symptoms usually begin 2–4 days after arrival to high altitude and classically the 2nd night sleeping at high altitude.
    • Characterized by insidious onset with decreased exercise performance and recovery time, cough, dyspnea on exertion, and progressive worsening of symptoms, especially at night. Pink frothy sputum is usually a late finding.
    • May have a sudden onset, especially in sedentary individuals at altitude
  • HACE:
    • Previous symptoms of AMS, with progressive worsening of neurologic symptoms, including

      P.307



      ataxia, extreme lassitude, mental status changes, and coma

    • Is commonly associated with HAPE
    • Progression from mild AMS to HACE at altitude may be as fast as 12 hr but usually requires 1–3 days
    • HACE usually occurs above 3,000 m but has occurred as low as 2,100 m.
Physical Exam
  • AMS:
    • Specific physical findings are missing in mild AMS.
    • Tachycardia or bradycardia is possible.
    • BP can be normal.
    • Localized rales can be present but are not diagnostic.
    • Tortuous and dilated retinal veins and retinal hemorrhages may be present but are not diagnostic.
  • HAPE:
    • Cyanosis is common.
    • Crackles in right middle lobe are classic but can be anywhere in the lung field.
    • Tachycardia
    • Tachypnea
    • Low-grade fever
    • Orthopnea
  • HACE:
    • Inability to perform activities such as dressing or eating
    • Truncal ataxia demonstrated by poor heel-toe walking.
    • Mental status changes
    • Occasionally focal neurologic deficits
    • Fundoscopic examination can demonstrate papilledema and retinal hemorrhages (not diagnostic).
Diagnostic Tests & Interpretation
Imaging
  • HAPE:
    • Chest x-rays demonstrate fluffy and patchy infil-trates in the periphery of the lung fields with a pre-dilection for the right middle lobe; normal heart size.
  • HACE:
    • Brain MRI is not necessary for diagnosis, but T2 images show an increased signal in the white matter, especially at the splenium of the corpus callosum.
Differential Diagnosis
  • AMS:
    • Dehydration
    • Exhaustion
    • Viral syndrome
    • Gastroenteritis
    • Hangover
    • Hypothermia
    • Carbon monoxide intoxication
    • Hyponatremia
  • HAPE:
    • Pneumonia
    • Asthma
    • Mucus plugging
    • Pulmonary embolus
    • Congestive heart failure
    • Myocardial infarction
    • Uncomplicated HAPE usually does not present with high fever >101°F, chills, or mucopurulent sputum.
  • HACE:
    • Same as those for AMS as above
    • Cerebrovascular accident
    • Intoxication
    • Brain tumors
    • CNS infection
    • Acute psychosis
Treatment
  • Altitude illnesses in general: Descent to a lower altitude is the mainstay of treatment.
  • Mild AMS:
    • No further ascent until symptoms resolve; consider descent of at least 500 m.
    • Limit physical exertion and maximize hydration.
    • Symptomatic medications: NSAIDs, aspirin, acetaminophen for headache and antiemetics for nausea/vomiting
    • Acetazolamide 125–250 mg PO b.i.d. to help speed the acclimatization process
  • Moderate-to-severe AMS or continued mild symptoms:
    • In addition to treatment of mild AMS, consider low-flow oxygen at 2–4 L/min.
    • Acetazolamide 125–250 mg b.i.d. with or without dexamethasone 4 mg PO, IM or IV q6h
    • After stopping dexamethasone, ensure the patient remains symptom-free for 24–48 hr before re-ascending, as rebound symptoms of AMS can occur after discontinuation of steroid.
    • Consider use of Gamow bag if O2 is not available or if symptoms are severe or not improving or if immediate descent is not possible. A Gamow bag is a fabric pressure (hyperbaric) bag that the patient is placed in that can be manually inflated. When inflated to 2 psi, the internal environment of the bag simulates a descent of 1,000–3,000 m, depending on starting altitude.
  • HAPE:
    • Assisted descent immediately
    • Minimize exertion; keep patient warm.
    • Early recognition of HAPE symptoms is essential to initiate immediate descent and oxygen.
    • Concomitant use of high-flow oxygen at 4–6 L/min is essential, if available.
    • Consider nifedipine 10 mg PO every 4 hr by titration to response or 10 mg PO once followed by 30 mg extended-release q12–24h.
    • Inhaled beta agonist
    • Consider sildenafil 50 mg PO q8h
    • Gamow bag: Hyperbaric therapy for 4–6 hr can be used if immediate descent is impossible and oxygen is unavailable or symptoms not improving; symptomatic medications as for AMS can be used.
    • Observe for symptoms of HACE.
  • HACE:
    • Immediate descent is mandatory.
    • Oxygen at 2–10 L/min
    • Dexamethasone 4 mg PO, IM or IV every 6 hr
    • Gamow bag can be used if descent is delayed or if athlete is unable to descend.
    • Observe for symptoms of HAPE.
    • After descent, hospitalization is recommended.
Complementary and Alternative Medicine
Ginkgo biloba and antioxidants have both been looked at as possible alternative treatments and/or preventative measures for AMS. Results for both have been mixed, and both deserve further study.
Ongoing Care
  • General preventative measures:
    • Avoid heavy exertion for 2–3 days upon arrival to high altitude.
    • Maintain adequate hydration.
    • Eat frequent, small, high-carbohydrate meals.
    • Avoid alcohol.
    • Avoid sedatives/hypnotics.
    • Avoid smoking.
    • Avoid daytime sleeping.
  • Acclimatization:
    • Planned acclimatization is the physiologic method of progressively increasing sleeping altitude.
    • Proper acclimatization can prevent serious altitude illness.
    • “Climb high and sleep low.” See the “General Prevention” section above for specific acclimatization guidelines.
    • If a rapid ascent to 3,000 m or more is unavoidable, or if there is a previous history of AMS or HAPE, acetazolamide can be used to help prevent or speed up the acclimatization process. Acetazolamide 125 mg PO b.i.d.–t.i.d. is most commonly supported for prevention means.
Additional Reading
1991 International Hypoxia Symposium held at Lake Louise in Alberta Canada.
International Society of Mountain Medicine Web site
Sutton JR, Coates G, Houston CS, eds. 1992. “The Lake Louise Consensus on the Definition and Quantification of Altitude Illness.” In Hypoxia and mountain medicine. Burlington, Vermont: Queen City Printers.
Hackett PH, Roach RC. High altitude cerebral edema. High Alt Med Biol. 2004;5:136–146.
Hackett PH, Roach RC. High altitude medicine. In: Auerbach PS, ed. Wilderness medicine 5th ed. St. Louis: Mosby, 2007.
Levine BD, Stray-Gundersen J. “Living high-training low”: effect of moderate-altitude acclimatization with low-altitude training on performance. J Appl Physiol. 1997;83:102–112.
Levine BD, Stray-Gundersen J. A practical approach to altitude training: where to live and train for optimal performance enhancement. Int J Sports Med. 1992;13(Suppl 1):S209–S212.
Schoene RB. Illnesses at high altitude. Chest. 2008;134:402–416.
Stray-Gundersen J, Chapman RF, Levine BD. Hi lo altitude training improves performance in elite runners. Med Sci Sports Exerc. 1998;30:s35.
Codes
ICD9
993.2 Other and unspecified effects of high altitude
Clinical Pearls
  • Proper acclimatization (a graded ascent) is the best method for preventing altitude-related illnesses.
  • Athletes who participate in highly aerobic sports/events at low altitudes will benefit most from the “train low, sleep high” method of training.
  • Athletes who participate in aerobic sports/activities above 2,000 m will benefit from a short period of acclimatization before participation (5–20 days).
  • For athletes performing above 4,000 m, acclimati-zation at an intermediate altitude is recommended.
  • When at altitude, think altitude.
  • Early diagnosis of altitude illnesses is key, as treatment is much more successful the earlier the illness is diagnosed.
  • Acetazolamide given at 125–250 mg PO b.i.d. is a safe and effective way to help the acclimatization process and to treat AMS.


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