High-altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy people at altitudes typically above 2,500 meters (8,200 ft). However, cases have also been reported between 1,500–2,500 metres or 4,900–8,200 feet in more vulnerable subjects. Classically, HAPE occurs in persons normally living at low altitude who travel to an altitude above 2,500 meters (8,200 feet). Re-entry HAPE is also an entity that has been described in persons who normally live at high altitude but who develop pulmonary edema after returning from a stay at low altitude. It is severe presentation of altitude sickness. There are many factors that can make a person more susceptible to developing HAPE, including genetic factors, but detailed understanding is lacking and currently under investigation. HAPE remains the major cause of death related to high-altitude exposure, with a high mortality rate in the absence of adequate emergency treatment. Signs and symptoms
Physiological and symptomatic changes often vary according to the altitude involved.The Lake Louise Consensus Definition for high-altitude pulmonary edema has set widely used criteria for defining HAPE symptoms.In the presence of a recent gain in altitude, the presence of the following:
Symptoms: at least two of:

Shortness of breath at rest
Cough
Weakness or decreased exercise performance
Chest tightness or congestionSigns: at least two of:

Crackles or wheezing (while breathing) in at least one lung field
Central blue skin color
Tachypnea (rapid breathing)
Tachycardia (rapid heart rate)Acute mountain sickness and high altitude cerebral edema may also be present in conjunction with HAPE, however these symptoms may be subtle or not present at all.
Imaging studies such as X-ray and CT imaging of the chest may reveal thoracic infiltrates that can be seen as opaque patches. One distinct feature of HAPE is that pulse oximetry saturation levels (SpO2) are often decreased from what would be expected for the altitude. People typically do not appear as ill as SpO2 and chest X-ray films would suggest. Giving extra oxygen rapidly improves symptoms and SpO2 values; in the setting of infiltrative changes on chest X-ray, this is nearly pathognomonic for HAPE. Severity
The severity of HAPE is graded. The grades of mild, moderate, or severe HAPE are assigned based upon symptoms, clinical signs, and chest x-ray results for individuals. The symptoms that are taken in to account while evaluation the severity of HAPE are difficulty breathing while exerting or while at rest, the presence of a cough and the quality of that cough, and the level of fatigue of the patient. On physical exam of a suspected HAPE patient the exam findings used to grade the severity are the heart rate, respiratory rate, signs of cyanosis, and severity of lung sounds. Both symptoms and signs on physical exam can be used to evaluate a patient in the field. Chest X-rays are also used to evaluate the severity of HAPE when they are available. Differential diagnosis
Differential diagnosis:
Pneumonia
Bronchitis
Mucous plugging
Pulmonary embolism
Acute coronary syndrome
Acute decompensated heart failure
Asthma
Reactive airway disease
Exercise-associated hyponatremia
Pneumothorax

Prevention
The primary recommendation for the prevention of HAPE is gradual ascent.