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ESSENTIALS OF DIAGNOSIS

  • The severity of the high-altitude illness is affected by the rate and height of ascent and the individual’s susceptibility.

  • Prompt recognition and medical treatment of early symptoms of high-altitude illness may prevent progression.

  • Clinicians must assess other conditions that may coexist or mimic symptoms of high-altitude illness (eg, severe dehydration, hyponatremia, hypoglycemia, trauma, infection).

  • Immediate descent is the definitive treatment for high-altitude cerebral edema and high-altitude pulmonary edema.

General Considerations

As altitude increases, there is a decrease in both barometric pressure and oxygen partial pressure resulting in hypobaric hypoxia. High-altitude illnesses are due to hypobaric hypoxia at high altitudes (usually greater than 2000 meters or 6562 feet). High-altitude illness includes a spectrum of disorders categorized by end-organ effects (mostly cerebral and pulmonary) and exposure duration (acute and long-term). Acute high-altitude illnesses are acute hypoxia, acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). Long-term exposure to high altitude over months or years with inadequate acclimatization can result in subacute mountain sickness and chronic mountain sickness (Monge disease).

Acclimatization occurs as a physiologic response to the increasing altitude and increasing hypobaric hypoxia. Physiologic changes include increases in alveolar ventilation and oxygen extraction by the tissues and increased hemoglobin level and oxygen binding. High-altitude illness results when the hypoxic stress is greater than the individual’s ability to acclimatize. This is a result of fluid shifts from intravascular to extravascular spaces, especially in the brain and lungs. Risk factors for high-altitude illness include increased physical activity with insufficient acclimatization, inadequate education and preparation, individual susceptibility (preexisting medical conditions and medication use), and previous high-altitude illness. The key determinants of high-altitude illness risk and severity include both individual susceptibility factors and altitudinal factors, such as rate and height of ascent and total change in altitude over time. Presentations may be acute, subacute, or chronic disturbances that result from hypobaric hypoxia. Acclimatization to altitudes above 5500 meters (18,045 feet) is incomplete or physiologically impossible, although individual differences in tolerance to hypoxia exist.

Individual susceptibility factors include underlying conditions such as cardiac and pulmonary disease, patent foramen ovale, blood disorders (eg, anemia, sickle cell disease), pregnancy, neurologic conditions, smoking, recent surgery, diabetes, and many other chronic medical conditions. Those with symptomatic neurologic, cardiac, or pulmonary disease must avoid high altitudes.

Patient assessment for high-altitude illness must also include evaluation for other conditions (eg, severe dehydration, hyponatremia, hypoglycemia, infection, or trauma), which may coexist or may present in a similar manner.

1. HIGH-ALTITUDE–ASSOCIATED NEUROLOGIC CONDITIONS: AMS & HACE

There is a spectrum of neurologic conditions caused by high altitude, ranging from acute mountain sickness (AMS) to the more serious form, high-altitude cerebral edema (HACE) Clinicians may utilize various diagnostic tools to assess the level of cerebral impairment due to high altitude (visual analog scale [VAS] score, Acute Mountain Sickness-Cerebral [AMS-C] score, clinical functional score ...

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