From the Guidelines
Acute Mountain Sickness (AMS), High Altitude Cerebral Edema (HACE), and High Altitude Pulmonary Edema (HAPE) are distinct altitude-related illnesses that differ in severity, symptoms, and affected body systems, with AMS being the mildest form and HACE and HAPE involving life-threatening organ failure if not treated promptly. The key differences between these conditions lie in their pathophysiology and clinical presentation. AMS is characterized by headache, nausea, fatigue, dizziness, and sleep disturbances, typically occurring above 8,000 feet and resolving with acclimatization, rest, or descent 1. HACE is a severe progression of AMS, involving brain swelling, marked by confusion, ataxia, severe headache, and altered mental status, requiring immediate descent and treatment with dexamethasone (8mg initially, then 4mg every 6 hours) 1. HAPE affects the lungs, causing fluid accumulation that leads to shortness of breath, dry cough, chest tightness, extreme fatigue, and decreased exercise performance, with treatment including immediate descent, supplemental oxygen, and nifedipine (10mg initially, then 30mg extended-release every 12-24 hours) 1.
Key Characteristics of Each Condition
- AMS: Milder systemic response to hypoxia, characterized by headache, nausea, fatigue, and sleep disturbances.
- HACE: Severe progression of AMS, involving brain swelling, confusion, ataxia, and altered mental status.
- HAPE: Involves fluid accumulation in the lungs, leading to shortness of breath, dry cough, and chest tightness.
Prevention and Treatment
Prevention of these conditions involves gradual ascent to allow for acclimatization, with recommendations for maximum rate of ascent above 2,500 meters 1. Treatment for HAPE includes immediate descent, supplemental oxygen, and nifedipine, while HACE requires immediate descent and dexamethasone. For patients with pre-existing cardiovascular conditions, assessment of safety for high altitude exposure should depend on their functional capacity at sea level, with certain medications potentially interfering with physiological adaptation processes at high altitudes 1.
Clinical Considerations
Patients with heart failure are more susceptible to the physiological changes induced by high altitude exposure and should have their safety for high altitude travel assessed based on their functional capacity at sea level 1. Certain drugs prescribed for heart failure can interfere with physiological adaptation processes at high altitudes, and patients with conditions such as anaemia or muscle loss require special considerations when planning to travel to high altitude locations.
From the Research
Definition and Distinction of High Altitude-Related Illnesses
- Acute Mountain Sickness (AMS) is a common syndrome that occurs when the body cannot adapt to high altitudes, causing symptoms such as headache, nausea, and fatigue 2, 3.
- High Altitude Cerebral Edema (HACE) is a more severe and rare condition characterized by swelling of the brain, which can be life-threatening if not treated promptly 2, 4.
- High Altitude Pulmonary Edema (HAPE) is another severe condition that occurs when fluid builds up in the lungs, making it difficult to breathe 2, 5.
Pathophysiology and Risk Factors
- High altitude-related illnesses are caused by hypoxia and hypoxemia, which can lead to increased permeability of the blood-brain barrier and fluid buildup in the lungs and brain 3, 4.
- Individual susceptibility to high altitude-related illnesses is a significant risk factor, and people with preexisting medical conditions, such as heart and lung diseases, are more vulnerable 2, 6.
- Rapid ascent to high altitudes without sufficient acclimatization is a common feature of acute altitude illness 3, 5.
Diagnosis and Treatment
- Diagnosis of high altitude-related illnesses is based on clinical symptoms and physical examination, and treatment involves oxygen therapy, descent to lower altitudes, and supportive care 2, 5.
- In populated highland cities, descent is not always mandatory, and treatment can be provided with adequate medical resources 5, 6.
- Prevention of altitude-related illness is the best approach, and slow ascent, acclimatization, and medical advice can help reduce the risk of developing these conditions 2, 3.