high altitude pulmonary edema HAPE

The video clip shows a B-line pattern that is reported to be diffusely distributed throughout all lung fields. Pulmonary edema is the most likely diagnosis, in this case related to high altitude (choice C is correct). Pulmonary edema caused by heart failure would have an identical appearance on ultrasound. B-lines indicate an alveolar interstitial pattern and are nonspecific as to the cause creating this pattern. They may be seen with pulmonary edema, interstitial lung disease, and infection.

The treatment of high-altitude pulmonary edema (HAPE) includes rest, administration of oxygen, and descent to a lower altitude. It carries a 20% mortality and is an emergency. It is usually seen starting at approximately 2,438 m (8,000 feet) but can be seen at any altitude >1,524 m (>5,000 feet). If diagnosed early, recovery is rapid with a descent of only 500 to 1,000 m (3,000 feet). A portable hyperbaric chamber or supplemental oxygen administration immediately increases oxygen saturation and reduces pulmonary artery pressure, heart rate, respiratory rate, and symptoms. In situations where descent is difficult, these treatments can be lifesaving.

At high altitude, systolic pulmonary artery pressure increases less in participants who received dexamethasone (16 mm Hg) and tadalafil (13 mm Hg) than in those who received placebo. Prevention of HAPE is achieved most effectively by gradual ascent, allowing time for proper acclimatization. Certain prophylactic medications may further reduce the risk of ascending to high altitude in individuals with a history of HAPE. Prophylaxis with nifedipine or tadalafil has been studied, but is not frequently used.

The diagnosis of pneumothorax is excluded by the presence of B-lines or sliding lung (choice A is incorrect). A-lines and absence of sliding lung would be found if there were air in the pleural space, such as in a pneumothorax (video). Pulmonary contusion and aspiration pneumonia would both show a consolidation pattern (video) or a scattered B-line morphology intermixed with A lines (choices B and D are incorrect).

This patient would be considered high risk for acute mountain sickness (AMS) because of his intent to perform a rapid ascent. Therefore, pharmacologic prophylaxis is recommended. Although acetazolamide would typically be first line therapy for this indication, in the case in which an individual has documented to have prior anaphylaxis with use of sulfonamides (a class of medication that has been reported to have cross-reactivity with acetazolamide), even if the association is seemingly weak, a conservative course is recommended. This is due to the fact that the aceazolamide would likely be started in unfamilar locale without robust medical services available. To that end, dexamethasone is recommended as a second line prophylactic therapy at a dose of either 2 mg every 6 hours or 4 mg every 12 hours (choice D is correct).

Several studies have been published that refuted the cross-reactivity for the sulfonamides, and at least one study of testing for acetazolamide sensitivity in patients before travel has been reported. However, lack of readily accessible medical support at remote high-altitude locations if true anaphylaxis would occur suggests taking a careful approach for prescribing prophylactic medication for AMS in the situation where a severe sensitivity to sulfonamides is known (choice C is incorrect).

Travel to elevations greater than 8,200 feet (2,500 m) is associated with risk of developing one or more forms of acute altitude illness such as AMS, high altitude cerebral edema (HACE), and high altitude pulmonary edema (HAPE). Because many people travel to destinations that are situated at high terrestrial elevations, clinicians are often faced with questions from patients about the best means to prevent these disorders. The Wilderness Medical Society (WMS) convened an expert panel and published evidence-based guidelines with an update for prevention and treatment of acute altitude illness. In the guidelines, patients are classified into low, moderate, or high-risk groups for developing illness and specific recommendations are provided for prophylaxis of clinical symptoms.

The guidelines emphasize the importance of a gradual ascent as a primary strategy for AMS prevention. Several studies have shown that repeated exposure to hypobaric or normobaric hypoxia in the time preceding a high altitude excursion (referred to as "preacclimatization") or spending up to 6 to 7 days at a moderate altitude (approximately 2,200–3,000 m, or 7,218–9,843 ft) before proceeding to higher altitudes (referred to as "staged ascent") decreases the risk of AMS, improves ventilation and oxygenation, and blunts the pulmonary artery pressure response after subsequent ascent to higher altitudes.

Risk for development of AMS is classified into three categories:

Low risk includes those individuals with no prior history of altitude illness who plan to ascend to altitudes of less than 2,800 m (9,186 ft), and those taking more than 2 days to arrive at 2,500 to 3,000 m (8,200-9,843 ft) with subsequent increases in sleeping elevation less than 500 m (1,600 ft) per day plus an extra day for acclimatization every 1,000 m (3,280 ft).

Moderate risk includes travelers with a prior history of AMS and ascending to 2,500 to 2,800 m (8,202–9,186 ft), no history of AMS and ascending to a height greater than 2,800 m (9,186 ft) in one day, or any individual ascending more than 500 m (1,600 ft) per day at altitudes above 3,000 m (9,842 ft) but with an extra day for acclimatization every 1,000 m (3,280 ft).

High risk is present when an individual with a history of AMS ascends to an altitude of more than 2,800 m (9,186 ft) in one day, all individuals with a history of HACE, all individuals ascending to an altitude of 3,500 m (11,483 ft) in one day, all individuals ascending at a rate of more than 500 m (1,600 ft) per day above 3,000 m (9,842 ft) without extra days for acclimatization, or very rapid ascends such as scaling Mount Kilimanjaro in less than 7 days.

Although ibuprofen has been shown to be more effective than placebo in affecting acute mountain sickness prophylaxis using 600 mg three times daily, no trials were performed comparing it to acetazolamide and no other trials have specifically shown improved prevention efficacy (choice A is incorrect). Another drug utilized to prevent acute mountain illness is ginkgo biloba. Although several trials have demonstrated a benefit of ginkgo in AMS prevention, several well-designed but negative trials make its use indeterminate and therefore potentially useful but unproven when compared to other choices (choice B is incorrect).

As an aside, travelers to remote areas where malaria is endemic also need to consider dose adjustment of antimalarial medications if taking dexamethasone.