In climbers who had previously developed HAPE, re-attack rate was up to 60% with ascent to 4,559 metres (14,957 ft) in a 36-hour time period, though this risk was significantly reduced with slower ascent rates. It is believed that up to 50% of people suffer from subclinical HAPE with mild edema to the lungs but no clinical impairment. History
HAPE was recognized by physicians dating back to the 19th century but was originally attributed to “high altitude pneumonia”. The first documented case of pulmonary edema, confirmed by autopsy, was probably that of Dr Jacottet who died in 1891 in the Observatoire Vallot below the summit of Mont Blanc. After participating in a rescue on the mountain, the doctor refused to return. Instead, he spent further two nights at an altitude of 4,300 metres (14,100 ft) with obvious AMS symptoms and died on the second night. This condition was subsequently noticed in otherwise healthy climbers who would die shortly after arriving at high altitudes. It was not until 1960 that Charles Houston, an internal medicine physician in Aspen, published a case report of 4 individuals participating in high elevation activities that he had diagnosed with “edema of the lungs”. He described chest X-rays with edema and non-specific changes on EKG. Even though these cases had been termed high altitude pneumonia in the past, Houston indicated that these cases were “acute pulmonary edema without heart disease”. Research
To help understand factors that make some individuals susceptible to HAPE, the International HAPE Database was set up in 2004.
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.