High Altitude Pulmonary Edema

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Introduction   

High altitude pulmonary edema (HAPE) is a severe and extreme form of altitude sickness that occurs in otherwise healthy adults. This condition typically occurs at altitudes of greater than 2,500 meters (8,200 feet) and is characterized by fluid buildup in the lungs secondary to hypoxia. HAPE can be fatal if not treated.  

This condition typically occurs in individuals who live at lower altitudes and then travel to high altitudes. There are some predisposing risk factors that make a person more vulnerable to HAPE. Knowledge of the condition, its risk factors, presentation, and treatment is particularly useful for nurses and healthcare professionals working in or near high altitude areas as they are more likely to encounter this condition in their client population.  

This course aims to provide a foundation of knowledge for clinicians who are likely to encounter high altitude pulmonary edema and need to be familiar with its unique characteristics.  

Epidemiology 

Mountainous regions in the United States are popular destinations for tourism and recreation for around 40 million people annually. There are also 140 million people reported nationally as permanent residents above 2500 meters. Given that information, the occurrence of HAPE is generally very low, though it varies by region and is difficult to track consistently (10).  

In Colorado, it is estimated that only about 1 out of every 10,000 skiers will experience the condition (2). Mt Denali in Alaska, the tallest peak in the United States, has an incidence of HAPE in 1 of every 500 climbers. The European Alps have an incidence rate of around 0.2% of climbers (1), whereas the Himalayas in Asia may be as high as 4% (9). In general, the incidence above 2,200 meters is less than 1 in every 100 climbers (2).  

HAPE can occur at altitudes as low as 2000 meters, however the incidence and severity of illness increase with the altitude. At 4500 meters, the incidence is 0.6%-6% of individuals. At 5500, the incidence increases to 2%-15%. The rate of ascent also plays a role and those with faster ascent times have a higher risk of disease (6).  

In addition to high altitude and rapid ascent, individual risk factors include male sex, use of sleep medications, high sodium diet, and previous incidence of HAPE. A person who has experienced HAPE before has a recurrence rate of up to 60%. A medical history of cardiovascular conditions like hypertension, increased pulmonary vascular resistance, or a patent foramen ovale all increase the risk of HAPE. Environmental risk factors include cold temperatures and physically taxing routes (6).  

Though rare, the condition is serious and has a mortality rate of up to 50%. Even with proper treatment, the mortality rate can still be as high as 11%. Comorbid conditions include motion sickness in 50% of cases and cerebral edema in 14% of cases (6).  

Pathophysiology 

In order to understand HAPE, there must first be an understanding of the difference in oxygenation at various altitudes. At sea level, the concentration of oxygen in 1 liter of air is 21%. While the actual concentration is the same at 4000 meters, there is decreased barometric pressure due to the high altitude, which allows the oxygen molecules to spread out, meaning there is only about 63% of the usual oxygen available for each breath taken at high altitude. In order to maintain adequate oxygenation of organs and tissues, there are many physiologic adaptations that must take place at high altitudes (6).  

Studies show that genetics play a role in the ways people of various mountainous regions have adapted to the hypoxia of high altitude, usually with some combination of adjusted respiratory rate, increased oxygen carrying capacity of hemoglobin, and increased hemoglobin concentration. For people travelling to high altitude for short periods of time, the immediate response of the body is to increase the respiratory rate to obtain more oxygen from the thin air; this is known as the hypoxic ventilatory response (HVR). This causes respiratory alkalosis and shifts the oxygen-dissociation curve to the left, increasing hemoglobin’s binding capacity for oxygen. Within a couple of days, the body begins to stabilize this effect and allow for more adequate delivery of oxygen to the tissues. Still, it can take as much as 1-2 weeks for the body to increase the concentration of hemoglobin and improve oxygen transport that way (6).  

In some cases, the HVR may be blunted, either from factors like sedative medications or a genetic predisposition, and further hypoxia occurs. While many other organs respond to hypoxia with vasodilation in order to enhance oxygenation, the lungs actually respond with pulmonary vasoconstriction to shunt blood away from poorly oxygenated areas of the lung towards healthy alveoli. This compensatory response works well for focal conditions like pneumonia, but is ineffective in the generalized hypoxia of high altitude. As widespread pulmonary vasoconstriction occurs, increased perfusion and hydrostatic pressure on the alveoli damages the blood-gas barrier, increasing vascular permeability and allowing fluid and protein leakage and buildup in the alveoli; known as pulmonary edema (6, 10).  

From there, the fluid buildup further impedes oxygen delivery and worsening hypoxia. This triggers further pulmonary vasoconstriction, worsening pulmonary hypertension, and increased capillary pressure in a dangerous positive feedback loop. Without intervention, the condition will continue to worsen and can be fatal (6, 10).  

Clinical Presentation 

Given the fluid buildup in the lungs and progressively worsening hypoxemia, it is no surprise that the majority of symptoms of HAPE are respiratory in nature. Common presentation includes cough, shortness of breath, tachypnea, tachycardia, and cyanosis. Cough may begin as dry and progress to pink and frothy as pulmonary edema and alveolar damage progresses. Activity intolerance and extreme fatigue are also hallmark symptoms of HAPE. There may also be lower extremity swelling, syncope, and hemoptysis (3, 6, 10).  

On exam, pulse oximetry may be as much as 10% less than expected for altitude, crackles or wheezing may be present on auscultation, and jugular vein distention may be present. Chest x-ray will often reveal diffuse “fluffy” or “patchy” infiltrates. Despite low SPO2 and poor chest x-ray, clients usually do not appear as ill as would be expected. Electrocardiogram may be consistent with right sided heart failure and show right ventricular hypertrophy, right bundle branch block, or tall p-waves. Echocardiogram may show a dilated right side of the heart and increased pulmonary artery pressure (6, 10).  

Treatment 

The first line treatment for HAPE includes supplemental oxygen and descending to a lower altitude by up to 1000 meters as soon as possible. Symptom resolution should be notable as affected individuals descend. Clients with rapidly progressing symptoms while mountain climbing may need evacuation by emergency personnel, especially since continued exertion will only worsen symptoms. Portable hyperbaric chambers may be used to increase the barometric pressure around a client and improve oxygenation while awaiting descent and transport to a healthcare facility. Keeping clients warm is also important as hypothermia will worsen progression of illness (3, 6, 10).  

Supplemental oxygen via high flow nasal cannula should improve SPO2 and symptoms fairly quickly. Medications like nifedipine and phosphodiesterase inhibitors can reduce pulmonary vasoconstriction and alleviate symptoms if needed. 

Outcomes and Complications 

Timely identification of symptoms and treatment with descent and supplemental oxygen is the best way to achieve positive outcomes. The condition is most often fatal for individuals who are unable to descend quickly enough or access lifesaving treatments such as oxygen and portal hyperbaric chambers. The condition can become fatal within just a few hours, resulting in a 50% mortality rate. Failure to be treated in a timely manner is often due to logistical problems with descending treacherous conditions or receiving medical care while on a strenuous hiking or climbing expedition (5).   

Prolonged exposure to high altitude and hypoxia may result in vascular remodeling and long-term pulmonary hypertension. People who live at high altitudes are more likely to experience this permanent effect than people visiting or climbing recreationally (6).  

Prevention is the best way to avoid poor outcomes. Fast ascent is one of the main risk factors, so not increasing elevation by more than 500 meters per day and including a rest day with no ascent at all every 3-4 days is recommended by the Wilderness Medical Society (WMS) (8). Additionally, avoiding strenuous hiking or ascent to high elevations for individuals taking sedative medications or with existing pulmonary vascular disorders is recommended.  

Role of the Nurse 

The nurse may play a vital role in cases of HAPE in a variety of unique ways. One of the first, and possibly most important, is prevention education. Nurses working in mountainous, high-altitude areas can provide community and public health education about the risks of HAPE, safe climbing protocols, signs and symptoms of the illness, and the importance of early identification and descent. By adequately preparing tourists, expeditioners, climbing groups, and others, cases of HAPE may be reduced or avoided (7).  

Community and individual assessment of locals living and working at high altitude may also help the nurse identify those at risk of slower, more permanent pulmonary vascular changes and hypertension. Identification of a similar, but chronic and less imminently lethal condition, high altitude pulmonary hypertension (HAPH) is important for clients remaining in high altitude locations long term (7).  

Nurses may also play a role in identifying and managing HAPE when it occurs. Being on the medical staff at ski resorts, mountain lodges, or even members of climbing expedition medical teams would allow nurses to monitor clients and pick up early signs of illness, assess the progression of illness, and implement treatment modalities such as supplemental oxygen administration (4).  

And finally, nurses working in the hospital setting may encounter clients who have fully descended and are seeking care for respiratory symptoms. HAPE can often be mistaken for other common respiratory conditions such as pneumonia, asthma, bronchitis, pulmonary embolism, and others. Knowledge of the unique characteristics of HAPE, including risk factors, should have nurses working in high altitude areas on high alert for the condition (4).  

Among identification of signs and symptoms of HAPE, nurses may be tasked with administering supplemental oxygen, assisting with portal hyperbaric chambers, administering medications like nifedipine, and monitoring clinical condition and SPO2 (4).  

Conclusion

HAPE is a serious, though rare, condition that occurs when the body has a poor adjustment to high altitude. While this condition is not likely to be encountered by nurses in many settings, those working in or near high altitude locations are much more likely to see it and must be prepared. Swift identification and treatment initiation of this condition can significantly improve outcomes and knowledgeable nurses are on the front lines to ensure care goes as smoothly as possible.  

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