+Expected SpO2 and PaO2 levels at<unk> <unk>  SpO2 PaO2 (mm Hg) about 90% 55–75 75–85% 40–60 58–75% 28–40 The diagnosis of<unk>  is entirely based on symptoms and many of the symptoms overlap with other diagnoses. Before<unk>  was understood it was commonly confused with pneumonia which resulted in inappropriate treatment.<unk>  generally develops in the first 2 to 4 days of hiking at<unk> s >2,500 meters (8,200 ft), and symptoms seem to worsen most commonly on the second night. Initial symptoms are vague and include shortness of breath, decreased exercise ability, increased recovery time, fatigue, and weakness, especially with walking uphill. People then develop a dry, persistent cough, and often cyanosis of the lips. Another cardinal feature of<unk>  is the rapid progression to dyspnea at rest. The development of pink, frothy, or frankly bloody sputum are late features of<unk> . In some cases, people will develop concomitant neurological features such as poor coordination, altered consciousness, or cerebral<unk>  (High-altitude cerebral<unk> . On physical exam, increased breathing rates, increased heart rates, and a low-grade fever 38.5o (101.3o F) are common. Listening to the lungs may reveal crackles in one or both lungs, often starting in the right middle lobe. 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<unk>  is that pulse oximetry saturation levels (SpO2) are often decreased from what would be expected for the<unk> . 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<unk> . Severity The severity of<unk>  is graded. The grades of mild, moderate, or severe<unk>  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<unk>  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<unk>  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<unk>  when they are available. Differential diagnosis Differential diagnosis: * Pneumonia * Bronchitis * Mucous plugging *<unk>  embolism * Acute coronary syndrome * Acute decompensated heart failure * Asthma * Reactive airway disease * Exercise-associated hyponatremia * Pneumothorax
High-altitude pulmonary edema
High-altitude cerebral edema
Decompression sickness
Chronic mountain sickness
Monofixation syndrome
Athletic heart syndrome
Pulmonary-renal syndrome
Cardiorenal syndrome