High-Altitude Pulmonary Edema - Causes, Symptoms, and Treatment

Introduction:

High altitude pulmonary edema is a life-threatening non-cardiogenic pulmonary edema and the most common fatal manifestation of severe high-altitude illness. Anyone who travels to high altitudes, whether a hiker, soldier or mountain climber, is at risk of developing a high-altitude illness.

High altitude pulmonary edema is the abnormal accumulation of plasma and some red blood cells in the lung air sacs due to the breakdown in the pulmonary blood-gas barrier, triggered by hypobaric hypoxia (the condition where the partial pressure of oxygen is reduced). High altitude illness may result from short-term exposure to more than 2000 - 2500 m (6562 - 8202 feet). High altitude pulmonary edema generally occurs 2 to 4 days after rapid ascent to altitudes above 2500 m. Certain factors such as cold weather and physical exertion are the predisposing factors.

What Are the Symptoms of High-Altitude Pulmonary Edema?

• Dyspnea with exertion and rest is associated with weakness and cough.

• Extreme fatigue.

• Tachycardia (increased heart rate).

• Tachypnea (rapid breathing) even at rest.

• Productive cough with frothy pink sputum.

• Rales (clicking or rattling sound in the lungs).

• Central cyanosis (generalized bluish discoloration of the mucous membrane of nails, lips, and skin all over the body due to lack of oxygen).

• Disproportionately low oxygen saturation is relative to altitude.

• Crackles on auscultation.

• Prominent P2 and right ventricular heave on auscultation or palpation.

• The earliest indications are decreased exercise tolerance, slow recovery from exercise, and dry cough.

• Worsens at night, and tachycardia and tachypnea occur (at rest).

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• Chest tightness or congestion.

• Low-grade fever.

• Respiratory alkalosis (a condition in which the amount of carbon dioxide in the blood is very low).

• Leukocytosis (increased white blood cell count).

• In severe cases, this condition may lead to changes in mental status, hypotension, and death.

If left untreated, high-altitude pulmonary edema can be a life-threatening condition. Patients may clear fluid rapidly and do not develop long-term complications after recovery.

What Is the Pathophysiology of High-Altitude Pulmonary Edema?

Though all forms of high-altitude illness are caused by hypobaric hypoxia leading to hypoxemia, the pathophysiology is not well understood. It is a noncardiogenic form of pulmonary edema resulting from a leak in the alveolar-capillary membrane. The various mechanisms involved are:

• Pulmonary arterial vasoconstriction.

• Elevated pulmonary artery pressure leads to circulatory shear forces and consequent permeability leakage.

• Antidiuresis is mediated by increased antidiuretic hormones, which contribute to fluid retention.

• The inciting factor appears to be excess hypoxia.

The ventilatory response can be divided into four phases:

1. First, increased response due to ascending altitude.

2. Subsequent courses over hours and weeks.

3. Deacclimatization on the descent.

4. Long-term response of high-altitude people.

The barometric pressure decreases with distance above the earth’s surface. Climbers have lived for several days at altitudes that may cause unconsciousness within seconds without acclimatization. Therefore, portable spirometry may provide clinically relevant information for high-altitude travelers.

What Is the Etiology of High-Altitude Pulmonary Edema?

Young adults and previously acclimatized people reascending to a high altitude following a short stay at a low altitude are highly predisposed to high altitude pulmonary edema. Other predisposing factors include:

• Cold weather.

• Male sex.

• Use of sleep medications.

• Excessive salt ingestion.

• Physical exertion at high altitudes.

Preexisting conditions that lead to the development of high-altitude pulmonary edema include:

• Pulmonary hypertension.

• Patent foramen ovale (a hole in between the left and right atrium of the heart).

• Increased pulmonary vascular reactivity.

• Conditions that lead to increased pulmonary blood flow.

How to Diagnose High Altitude Pulmonary Edema?

Laboratory Findings:

• The arterial blood gas test confirms severe hypoxemia and respiratory alkalosis with the partial pressure of oxygen ranging from 30 to 40 millimeters of mercury.

• Other findings include elevated levels of interleukin-1 receptor antagonist (IL-1ra), interleukin-6 (IL-6), and c-reactive protein (CRP).

• The systemic increase in the levels of these inflammatory markers stimulates inflammation.

Chest X-rays:

• Chest radiography reveals bilateral patchy infiltrates throughout the lung with predominant changes in the right middle lobe.

Ultrasonography:

• Chest ultrasonography demonstrates a comet-tail technique, which has also been shown in cardiogenic pulmonary edema, effectively evaluating the degree of pulmonary edema in high-altitude pulmonary edema patients.

Electrocardiography (ECG):

• Electrocardiography reveals a right-sided heart strain pattern suggestive of pulmonary hypertension or ischemia.

What Are the Treatment Approaches for High Altitude Pulmonary Edema?

• An early diagnosis helps quick recovery even with a descending altitude of 50 to 1000 meters.

• The oxygen level is increased immediately by administering supplemental oxygen therapy or a portable hyperbaric chamber. It also reduces the heart rate, pulmonary artery pressure, and respiratory rate.

• Supplemental oxygen and descent are the definitive therapies for all forms of altitude illness. However, due to climate or environmental issues, descent may not always be possible.

• Both Tadalafil and Dexamethasone decrease pulmonary artery pressure and reduce the incidence of high altitude pulmonary edema in adults with a previous history. Dexamethasone prophylaxis may also reduce the risk of acute mountain sickness in adults.

• Using an expiratory positive airway pressure mask improves oxygenation and may be used as a temporary measure.

• Trekkers widely use portable hyperbaric oxygen chambers. Patients should be closely monitored for rebound symptoms after hyperbaric treatments.

What Are the Preventive Measures for High Altitude Pulmonary Edema?

Educating travelers with the following principles to prevent serious complications from altitude illness:

• Being aware and gaining knowledge on early symptoms of altitude illness.

• If symptoms present, avoid moving to higher altitudes as this can worsen the condition.

• If the symptoms worsen, descend immediately instead of staying at the same altitude.

• Antibiotic prophylaxis (treatment or drugs taken to prevent the disease or condition) is indicated in patients who have already been identified with this illness or who must ascend rapidly to a high altitude.

• Acetazolamide and Dexamethasone are effective prophylaxis against high-altitude illnesses. These should be administered 24 hours before ascent and continued for 48-72 hours at altitude.

• Acetazolamide is considered the drug of choice because of its low incidence of adverse effects. It also has positive effects on hypoxic pulmonary vasoconstriction (constriction of small pulmonary arteries due to hypoxia) and other forms of high-altitude illnesses.

Other preventive measures include:

• Eating a high-carbohydrate diet.

• Slow ascent.

• Avoid heavy exertion at high altitudes.

• Avoiding alcohol and sedatives.

• Avoiding abrupt ascent to sleeping elevations higher than 3000 meters.

Conclusion:

Though severe complications arise in relation to high-altitude pulmonary edema, the condition can be easily managed with various treatment approaches to prevent life-threatening situations. Immediate improvement of oxygenation either by supplemental oxygen, hyperbaric treatment, or rapid descent is the effective treatment of choice for high-altitude pulmonary edema.