What Is a High Altitude-Related Disorder?
Altitude-related disorders refer to conditions that occur when a person travels to a high-altitude region, such as mountains, which results in hypoxia. It usually happens at altitudes higher than 8000 feet. Everyone traveling to an increased height is at risk irrespective of age, physical fitness, medical history, or previous altitude experience.
The high-altitude environment refers to an altitude over 1500 m (4800 feet). Moderate elevations range from 2,000 to 3,500 m (6,400 to 11,200 feet). In high altitudes, though the arterial oxygen saturation is balanced, due to the decrease in the level of PaO2 (partial pressure of oxygen), mild tissue hypoxia and altitude disorders occur.
The arterial oxygen saturation level is not maintained in the very high altitude range of 3500 to 5600 m (11,200 to 18,000 feet). Extreme hypoxemia (low-level oxygen) happens in this range of altitude even during sleep, during exercise, or with illness.
Extreme altitude range refers to 5,600 m or above. Failure to long-term acclimatization happens at these elevations. Individuals must slowly ascend to intermediate altitudes to reach extreme heights.
What Are the Types of Altitude Disorder?
Altitude disorder refers to a group of conditions due to hypoxia, namely acute mountain sickness (AMS), high altitude cerebral edema (HACE), and high altitude pulmonary edema (HAPE). Acute mountain sickness and high cerebral edema are related to brain pathophysiological conditions, whereas high altitude pulmonary edema (HAPE) is related to the lung.
There are three levels of altitude disorder:
Acute Mountain Sickness (AMS): It is the most familiar and mildest form that occurs within 6 to 12 hours of gaining altitude. The symptoms are:
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Headache.
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Dizziness.
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Muscle aches.
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Nausea.
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Anorexia.
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Difficulty sleeping.
High-Altitude Cerebral Edema (HACE): It is a manifestation of brain pathophysiology and happens when fluid retention occurs in the brain. It is one of the most severe and life-threatening conditions which even causes death. In some people, acute mountain sickness may progress to high altitude cerebral edema (HACE). Onset may start with worsening symptoms of acute mountain sickness and progresses to ataxia (impaired balance) and even to death.
High-Altitude Pulmonary Edema (HAPE): It is a build-up of fluid in the lungs that may be more dangerous and life-threatening and the most common cause of death from altitude sickness. This is non-cardiogenic pulmonary edema characterized by increased pulmonary capillary pressure and hypertension.
What Are the Causes of Altitude Disorder?
The pressure of the air that surrounds us is called barometric or atmospheric pressure. This atmospheric pressure decreases with higher altitudes, and significantly less oxygen is available. Our body needs time to adapt to the change in pressure.
The causes are as follows:
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Rapid ascent to high altitude.
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Higher altitude.
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Decreased hypoxic ventilatory response.
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Restricted pulmonary circulation due to vascular abnormalities in pulmonary arteries.
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Congenital absence of pulmonary artery.
What Are the Signs and Symptoms of High Altitude Disorder?
The symptoms of acute mountain sickness are as follows::
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Headache.
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Dizziness.
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Muscle aches.
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Nausea.
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Vomiting.
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Anorexia.
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Difficulty sleeping.
Signs and symptoms of high altitude cerebral edema (HACE):
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Altered mental status or ataxia with acute mountain sickness.
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Altered mental status without acute mountain sickness.
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Malaise.
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Headache.
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Lassitude (lack of energy).
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Difficulty in being oriented.
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Occasional focal deficits.
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Confusion.
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Drowsiness.
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Stupor.
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Coma.
Symptoms of high altitude pulmonary edema:
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Dry cough changes to a productive cough.
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Weakness.
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Dyspnea at rest.
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Chest tightness.
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Congestion.
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Central cyanosis.
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Crackles or wheezing.
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Tachycardia (increased heart rate).
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Tachypnea (increased breath or respiratory rate).
What Is the Pathogenesis of Altitude Illness?
High-Altitude Pulmonary Edema:
HAPE is a non-cardiogenic form of pulmonary edema caused due to changes in the alveolar-capillary membrane. The various mechanisms involved are: constriction of pulmonary arteries leads to increased pulmonary arterial pressure resulting in circulatory shear forces and fluid retention due to increased antidiuretic hormones. The inciting factor is excessive hypoxia.
Acute Mountain Sickness and High Altitude Cerebral Edema:
Hypoxia produces neuro-hormonal (nitric oxide, reactive cytokines, free radicals) and hemodynamic responses, leading to cerebral vasodilation and cerebral microvascular beds over perfusion. This build-up increases capillary pressure and capillary leakage leading to subsequent edema. Hypoxia induces free radical formation causing failure of the Na+/K+ ATPase (sodium, potassium, adenosine triphosphatase) pump resulting in calcium entering the cell and causing subsequent edema.
How to Prevent Altitude-Related Disorder?
General:
The accent rate and the previous history of altitude illness determine a person's susceptibility to altitude illness. Slow ascent to altitude is the cornerstone of prevention. Avoid rapid ascents to an altitude higher than 3,000 m and spend two or three nights at 2500 to 3,000 m before starting up with a further ascent. The altitude at which a person sleeps is also an important factor. The sudden ascent of 600 m should be prevented. Consumption of alcohol, physical exhaustion, and hypnotics should be avoided in order to prevent altitude illness.
Acetazolamide:
Acetazolamide, as given prophylactically, reduces the incidence of AMS. This carbonic anhydrase inhibitor causes metabolic acidosis. This drug increases minute ventilation and maintains oxygenation during sleep. Rapid ascent to altitudes more significant than 3000 m (one day or less), rapid gain in sleeping altitude (higher than 900 m), or a history of AMS are the indications of this drug. This drug decreases AMS incidence rapidly ascending altitudes greater than 4000. Acetazolamide, 125 to 250 mg twice a day, taken before ascent for 1 to 3 days. Side effects include hypersensitivity, polyuria, peripheral paresthesia, and bone marrow suppression.
Dexamethasone:
The use of Dexamethasone is controversial. However, it is indicated in the case of rescue cases involved in sudden rapid ascents.
What Are the Other Effects of Altitude on Chronic Illness?
Pulmonary Disease:
Patients with pulmonary disease can travel to moderate altitudes (3,000 m). However, pulmonary hypertension, sleep-related breathing disorders associated with lung disease, and hypoxemia are expected to worsen at higher altitudes. Therefore, patients with chronic obstructive pulmonary disease characterized by severe hypoxemia and those with pulmonary hypertension are advised not to travel to high altitudes.
Sickle Cell Disease:
Patients with sickle-cell disease, sickle cell hemoglobin C disease, and sickle cell-thalassemia characterized by vaso-occlusive conditions are at greater risk. Most of these people are unaware of their medical condition. People experience crises even at an altitude of about 1500 m. Use of supplemental oxygen and avoidance of altitude is recommended if altitude travel is unavoidable. Even if no prior episodes have occurred, supplemental oxygen is considered with known hemoglobinopathy.
Pregnancy:
Women with low-risk pregnancies have no difficulties traveling to altitudes of about 4,000 m.
Women with late-term and high-risk pregnancies should not travel to altitudes higher than 2,500 m. Conversely, the risk to the fetus should be insignificant during short-term exposure to moderate altitudes.
Conclusion:
Due to severe medical problems and unique susceptibilities, a few patients will be unable to travel to high altitudes. Therefore, continued research into altitude-related illness is needed to reveal the underlying pathophysiology and travel to high altitudes, including safe air travel.
