The pathophysiology of high altitude pulmonary edema

High-Altitude Pulmonary Edema in Ohio at an Elevation of 339 Meters

Background

HAPE (High-Altitude Pulmonary Edema) is a life-threatening form of high-altitude illness caused by noncardiogenic pulmonary edema. It has been most commonly reported in individuals who live at lower elevations and travel to elevations above 2500 m, typically in those who do so without any acclimatization. It can also occur in residents of high altitudes who descend to lower altitudes and then return to their native altitude without acclimatization. HAPE is more common in individuals with a history of prior HAPE, very rapid rates of ascent, upper respiratory illness, extreme exertion and cold environmental temperatures, Down’s Syndrome, obesity and congenital pulmonary anomalies.

Case Presentation

Our case discusses a patient presenting to an emergency department in Ohio with severe respiratory distress, hypoxia and a radiograph that showed pulmonary edema without cardiomegaly. Additional history revealed the patient had recently returned from Breckenridge, Colorado (an elevation of approximately 2926 m). The diagnosis of HAPE was recognized and he was appropriately treated. He was educated and will not be returning to high altitude without acclimatization in the future.

Conclusion

Upon literature review, there has never been a prior documented case of a patient in Ohio with HAPE. Providers must consider altitude illness when evaluating travelers from high altitude destinations, even when traveling to a very low altitude like Ohio, as symptoms may be unresolved by descent alone. This case emphasizes the importance of obtaining relevant historical data including a travel history. It also emphasizes the importance of avoiding early closure of the diagnostic process by only considering common conditions. Finally, the case emphasizes the potential danger of anchoring bias to previously encountered conditions.

Susceptibility to high-altitude pulmonary edema is associated with increased pulmonary arterial stiffness during exercise

High-altitude pulmonary edema (HAPE), a reversible form of capillary leak, is a common consequence of rapid ascension to high altitude and a major cause of death related to high-altitude exposure. Individuals with a prior history of HAPE are more susceptible to future episodes, but the underlying risk factors remain uncertain. Previous studies have shown that HAPE-susceptible subjects have an exaggerated pulmonary vasoreactivity to acute hypoxia, but incomplete data are available regarding their vascular response to exercise. To examine this, seven HAPE-susceptible subjects and nine control subjects (HAPE-resistant) were studied at rest and during incremental exercise at sea level and at 3,810 m altitude. Studies were conducted in both normoxic (inspired Po₂ = 148 Torr) and hypoxic (inspired Po₂ = 91 Torr) conditions at each location. Here, we report an expanded analysis of previously published data, including a distensible vessel model that showed that HAPE-susceptible subjects had significantly reduced small distal artery distensibility at sea level compared with HAPE-resistant control subjects [0.011 ± 0.001 vs. 0.021 ± 0.002 mmHg^-1; P < 0.001). Moreover, HAPE-susceptible subjects demonstrated constant distensibility over all conditions, suggesting that distal arteries are maximally distended at rest. Consistent with having increased distal artery stiffness, HAPE-susceptible subjects had greater increases in pulmonary artery pulse pressure with exercise, which suggests increased proximal artery stiffness. In summary, HAPE-susceptible subjects have exercise-induced increases in proximal artery stiffness and baseline increases in distal artery stiffness, suggesting increased pulsatile load on the right ventricle.NEW & NOTEWORTHY In comparison to subjects who appear resistant to high-altitude pulmonary edema, those previously symptomatic show greater increases in large and small artery stiffness in response to exercise. These differences in arterial stiffness may be a risk factor for the development of high-altitude pulmonary edema or evidence that consequences of high-altitude pulmonary edema are long-lasting after return to sea level.

Pharmacotherapy for Altitude-Related Illness

Altitude-related illness is a frequent cause of morbidity and occasional mortality among recreational sports travelers in the United States and throughout the world. High-altitude illness describes the cerebral and pulmonary syndromes (acute mountain sickness, high-altitude cerebral edema, and high-altitude pulmonary edema) that can occur in unacclimatized persons ascending too rapidly to high altitude. The pathogenesis of these syndromes is primarily hypobaric hypoxia that causes compensatory changes in the brain and lungs, resulting in hyperperfusion of microvascular beds, increased capillary pressure, and a microvascular leak with resulting edema and a characteristic constellation of symptoms. Prevention and treatment involve education about rate of ascent; diet; alcohol intake; physical activity; oxygen; hyperbaric chambers; and pharmacotherapy, including acetazolamide, dexamethasone, nifedipine, and salmeterol in selected circumstances.

High-altitude pulmonary edema at moderate altitude (< 2,400 m; 7,870 feet): a series of 52 patients

STUDY OBJECTIVES

To describe a group of patients who acquired pulmonary edema at a moderate altitude of 1,400 to 2,400 m.

DESIGN

Observational, retrospective chart review (1992-2000) of a series of 52 consecutive patients admitted for high-altitude pulmonary edema (HAPE) that occurred at 1,400 to 2,400 m.

SETTING

Emergency department of a community hospital in the French Alps (altitude, 500 m).

PATIENTS

Vacationing skiers who met criteria for altitude-related pulmonary edema, and in whom other causes (infectious, cardiogenic, neurogenic, and toxic) were excluded.

MEASUREMENTS AND RESULTS

All patients presented with signs of pulmonary edema. Diagnoses of infectious, cardiogenic, neurogenic, or toxic edema were ruled out in each patient. All patients were hypoxemic and had radiographic signs of pulmonary edema. Virtually all patients (96%) had dyspnea, and most (77%) had moist rales. All patients were treated with supplemental oxygen (3 to 12 L/min), bed rest, moderate fluid restriction, and continuous positive airway pressure. All recovered fully and were discharged after 4 +/- 2 days (mean +/- SD).

CONCLUSION

This study suggests that HAPE at moderate altitudes is more frequent than usually reported. Patients are likely to be young, vacationing men, with no history of prior disease. The disease has a favorable prognosis, and requires simple treatment and a short hospital stay.

A tragic report of probable high-altitude pulmonary edema in the Himalayas: preventive implications

High-altitude pulmonary edema (HAPE) is a well-recognized disease entity in trekkers to the Nepal Himalayas. We present the case of a patient who had clinical features consistent with HAPE but did not descend the mountain on time, which contributed to his death. The important factors of the diagnosis, the descent, and the follow-up in Kathmandu are examined.