High Altitude Pulmonary Edema
Encyclopedia
High altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema
(fluid accumulation in the lungs) that occurs in otherwise healthy mountaineers at altitudes typically above 2500 metres (8,202.1 ft).
Some cases, however, have been reported also at lower altitudes (between 1500–2500 m or 4,921.3–8,202.1 ft in highly vulnerable subjects), although what makes some people susceptible to HAPE is not currently known. HAPE remains the major cause of death related to high-altitude exposure with a high mortality in absence of adequate emergency treatment.
The Lake Louise Consensus Definition for High Altitude Pulmonary Edema has set widely-used criteria for defining HAPE symptoms:
Symptoms: at least two of:
Signs: at least two of:
Intermediate Altitudes (1500-2500 m or 4900-8200 feet)
Clinical symptoms are unlikely.
Blood oxygen levels remain >90%.
High Altitude (2500-3500 m or 8200-11500 feet)
Clinical symptoms are common and may develop after 2-3 days. Blood oxygen levels may drop below 90% or lower during exercise. Prior acclimatisation will decrease the severity of the symptoms.
Extreme Altitude (>5800 m or 19000 feet)
Blood oxygen levels are <90%, even at rest. Progressive deterioration may occur despite acclimatisation.
which is caused by the lower air pressure at high altitudes.
The mechanisms by which this shortage of oxygen causes HAPE are poorly understood, but two processes are believed to be important:
Although higher pulmonary arterial pressures are associated with the development of HAPE, the presence of pulmonary hypertension
may not in itself be sufficient to explain the development of edema
: severe pulmonary hypertension can exist in the absence of clinical HAPE in subjects at high altitude.
has exposed sea-level-resident volunteers rapidly and directly to high altitude; during 30 years of research involving about 300 volunteers (and over 100 staff members), only three have been evacuated with suspected HAPE.
. and nifedipine
Phosphodiesterase inhibitors such as tadalafil
are also effective but may worsen the headache of mountain sickness.
Pulmonary edema
Pulmonary edema , or oedema , is fluid accumulation in the air spaces and parenchyma of the lungs. It leads to impaired gas exchange and may cause respiratory failure...
(fluid accumulation in the lungs) that occurs in otherwise healthy mountaineers at altitudes typically above 2500 metres (8,202.1 ft).
Some cases, however, have been reported also at lower altitudes (between 1500–2500 m or 4,921.3–8,202.1 ft in highly vulnerable subjects), although what makes some people susceptible to HAPE is not currently known. HAPE remains the major cause of death related to high-altitude exposure with a high mortality in absence of adequate emergency treatment.
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:
Symptoms: at least two of:
- Difficulty in breathing (dyspneaDyspneaDyspnea , shortness of breath , or air hunger, is the subjective symptom of breathlessness.It is a normal symptom of heavy exertion but becomes pathological if it occurs in unexpected situations...
) at rest - Cough
- Weakness or decreased exercise performance
- Chest tightness or congestion
Signs: at least two of:
- Crackles or wheezing (while breathing) in at least one lung field
- Central cyanosisCyanosisCyanosis is the appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen. The onset of cyanosis is 2.5 g/dL of deoxyhemoglobin. The bluish color is more readily apparent in those with high hemoglobin counts than it is...
(blue skin color) - TachypneaTachypneaTachypnea means rapid breathing. Any rate between 12-20 breaths per minute is normal. Tachypnea is a respiration rate greater than 20 breaths per minute. - Distinction from other breathing terms :...
(rapid shallow breathing) - TachycardiaTachycardiaTachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...
(rapid heartrate)
Intermediate Altitudes (1500-2500 m or 4900-8200 feet)
Clinical symptoms are unlikely.
Blood oxygen levels remain >90%.
High Altitude (2500-3500 m or 8200-11500 feet)
Clinical symptoms are common and may develop after 2-3 days. Blood oxygen levels may drop below 90% or lower during exercise. Prior acclimatisation will decrease the severity of the symptoms.
Extreme Altitude (>5800 m or 19000 feet)
Blood oxygen levels are <90%, even at rest. Progressive deterioration may occur despite acclimatisation.
Causes
The initial cause of HAPE is a shortage of oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
which is caused by the lower air pressure at high altitudes.
The mechanisms by which this shortage of oxygen causes HAPE are poorly understood, but two processes are believed to be important:
- Increased pulmonary arterial and capillary pressures (pulmonary hypertensionPulmonary hypertensionIn medicine, pulmonary hypertension is an increase in blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries, together known as the lung vasculature, leading to shortness of breath, dizziness, fainting, and other symptoms, all of which are exacerbated by exertion...
) secondary to hypoxic pulmonary vasoconstrictionHypoxic Pulmonary VasoconstrictionHypoxic pulmonary vasoconstriction is a paradoxical, physiological phenomenon in which pulmonary arteries constrict in the presence of hypoxia without hypercapnia , redirecting blood flow to alveoli with a higher oxygen content.The process might at first seem illogical, as low oxygen levels should...
. - An idiopathicIdiopathicIdiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ἴδιος, idios + πάθος, pathos , it means approximately "a disease of its own kind". It is technically a term from nosology, the classification of disease...
non-inflammatory increase in the permeabilityVascular permeabilityVascular permeability, often in the form of capillary permeability, characterizes the capacity of a blood vessel wall to allow for the flow of small molecules or even whole cells in and out of the vessel. Blood vessel walls are lined by a single layer of endothelial cells...
of the vascular endotheliumEndotheliumThe endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...
.
Although higher pulmonary arterial pressures are associated with the development of HAPE, the presence of pulmonary hypertension
Pulmonary hypertension
In medicine, pulmonary hypertension is an increase in blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries, together known as the lung vasculature, leading to shortness of breath, dizziness, fainting, and other symptoms, all of which are exacerbated by exertion...
may not in itself be sufficient to explain the development of edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
: severe pulmonary hypertension can exist in the absence of clinical HAPE in subjects at high altitude.
Incidence
The incidence of clinical HAPE in unacclimatized travelers exposed to high altitude (~4000 m or 13,123.4 ft) appears to be less than 1%. The U.S. Army Pike's Peak Research LaboratoryUnited States Army Pike’s Peak Research Laboratory
The United States Army Pikes Peak Research Laboratory, or simply the “Pikes Peak Lab”, is a modern medical research laboratory for the assessment of the impact of high altitude on human physiological and medical parameters of military interest. It is a satellite facility of the U.S. Army Research...
has exposed sea-level-resident volunteers rapidly and directly to high altitude; during 30 years of research involving about 300 volunteers (and over 100 staff members), only three have been evacuated with suspected HAPE.
Predisposing factors
Individual susceptibility to HAPE is difficult to predict. The most reliable risk factor is previous susceptibility to HAPE, and there is likely to be a genetic basis to this condition, perhaps involving the gene for angiotensin converting enzyme (ACE). Recently, scientists have found the similarities between low amounts of 2,3-BPG (also known as 2,3-DPG) with the occurrence of HAPE at high altitudes.Research
In order to help understand the factors that make some individuals susceptible to HAPE, the International HAPE Database was set up in 2004. Individuals who have previously suffered from HAPE can register with this confidential database in order to help researchers study the condition.Treatment
The standard and most important treatment is to descend to lower altitude as quickly as possible, preferably by at least 1000 metres. Oxygen should also be given if possible. Symptoms tend to quickly improve with descent, but less severe symptoms may continue for several days. The standard drug treatments for which there is strong clinical evidence are dexamethasoneDexamethasone
Dexamethasone is a potent synthetic member of the glucocorticoid class of steroid drugs. It acts as an anti-inflammatory and immunosuppressant...
. and nifedipine
Nifedipine
Nifedipine is a dihydropyridine calcium channel blocker...
Phosphodiesterase inhibitors such as tadalafil
Tadalafil
Tadalafil is a PDE5 inhibitor, currently marketed in pill form for treating erectile dysfunction under the name Cialis; and under the name Adcirca for the treatment of pulmonary arterial hypertension...
are also effective but may worsen the headache of mountain sickness.
See also
- AcetazolamideAcetazolamideAcetazolamide, sold under the trade name Diamox, is a carbonic anhydrase inhibitor that is used to treat glaucoma, epileptic seizures, Idiopathic intracranial hypertension , altitude sickness, cystinuria, and dural ectasia...
, a drug which speeds up acclimatizationAcclimatizationAcclimatisation or acclimation is the process of an individual organism adjusting to a gradual change in its environment, allowing it to maintain performance across a range of environmental conditions...
to high altitudes. - Pulmonary EdemaPulmonary edemaPulmonary edema , or oedema , is fluid accumulation in the air spaces and parenchyma of the lungs. It leads to impaired gas exchange and may cause respiratory failure...
- Altitude sicknessAltitude sicknessAltitude sickness—also known as acute mountain sickness , altitude illness, hypobaropathy, or soroche—is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude...
- High altitude cerebral edemaHigh altitude cerebral edemaHigh altitude cerebral edema is a severe form of altitude sickness. HACE is the result of swelling of brain tissue from fluid leakage and almost always begins as acute mountain sickness...
(HACE) - High altitude flatus expulsionHigh altitude flatus expulsionHigh altitude flatus expulsion is a gastrointestinal syndrome which involves the spontaneous passage of increased quantities of rectal gases at high altitudes. First described by Joseph Hamel in c...
(HAFE) - Pulse oximeterPulse oximeterA pulse oximeter is a medical device that indirectly monitors the oxygen saturation of a patient's blood and changes in blood volume in the skin, producing a photoplethysmograph. It is often attached to a medical monitor so staff can see a patient's oxygenation at all times...
, the instrument to measure oxygen level in blood. - Wilderness medicineWilderness medicineWilderness medicine is defined by difficult patient access, limited equipment, and environmental extremes. Today, wilderness or expedition medicine is practiced by Wilderness First Responders, Wilderness EMTs, Remote/Offshore/Wilderness Paramedics and Physicians on expeditions, in outdoor...
- Wilderness Medical SocietyWilderness Medical SocietyThe Wilderness Medical Society was created on the 15th of February 1983 by three doctors from California--Dr Paul Auerbach, Dr Ed Geehr, and Dr Ken Kizer. It provides advice and guidance to medical personnel working in wilderness or backcountry environments...