Altitude illness

As the name implies, altitude illness develops in association with exposure to high altitude. Individual responses to altitude vary, even from ascent to ascent. Altitude illness can affect anyone, even those in optimal health. Children under age 6 are more susceptible to altitude illness than older children and adults.


Causes/associated factors
The physiological cause of altitude illness isn't entirely clear. Here's what we do know. When altitude increases, barometric pressure progressively decreases. This decreases the amount of available oxygen in the air you breathe. Adjustment to changes in altitude can be affected by:
rate and length of time spent in ascent
highest altitude reached
individual susceptibility, such as a history of altitude illness or a chronic illness (for example, heart or lung disease or conditions associated with abnormal hemoglobin, a protein in the red blood cells that carries oxygen)

Types of altitude illness
There are three primary types of altitude illness.
Acute mountain sickness (AMS) is considered a synonym for general altitude illness. This common condition develops most often above 10,000 feet above sea level. AMS is uncommon below 8,000 feet, but symptoms can develop at levels as low as 6,900 feet in certain people.

High altitude pulmonary edema (HAPE) is an abnormal buildup of fluid in the lungs that can develop from rapid ascent to altitudes above 9,500 feet above sea level. This potentially fatal condition develops in 5 to 10 percent of people who have acute mountain sickness, primarily when they ascend to more than 14,500 feet. Children who have respiratory infections are more prone to this condition. Generally, men tend to develop HAPE more often than women.

High altitude cerebral edema (HACE) is the least common but most serious of the three. It's characterized by neurological changes caused by swelling of the brain, usually after two to three days of remaining at a high altitude. If it progresses, the swelling may cause permanent injury or death. HACE develops in about 1.5 percent of people who have acute mountain sickness.
Other high altitude syndromes include:

peripheral edema (swelling of the face, hands and feet)
pharyngitis (inflammation and soreness of the throat)
bronchitis (inflammation of the lining of the large air passages in the lungs, characterized by a dry, hacking cough that can progress to severe coughing spasms)
ultraviolet keratitis or snow blindness (Ultraviolet light penetrates the atmosphere in higher degrees at high altitudes. This UV radiation can burn the cornea of the eye.)
fainting
transient ischemic attack (TIA, often called a "mini-stroke") and stroke

Signs/symptoms
Symptoms can range from mild distress to extreme or potentially fatal complications, especially for people who have preexisting conditions.
Symptoms of acute mountain sickness may include:

headache of varied severity (may worsen when you strain or bend over)
low energy
poor appetite
nausea or vomiting
dizziness
weakness
sleeping disturbances
irritability
shortness of breath with physical exertion
sleep apnea (a group of serious sleeping disorders in which breathing stops repeatedly for a period of time during sleep)
Symptoms of high altitude pulmonary edema may include:

extreme shortness of breath with physical exertion
shortness of breath at rest
dry or frothy cough
wheezing
rapid pulse
rapid breathing or breathing irregularities
wet, crackling lung sounds
disorientation
Symptoms of high altitude cerebral edema may include:

dizziness
vomiting
irritability
worsening headache with no relief from analgesics
poor coordination
disorientation
confusion
hallucinations
extreme sleepiness with difficulty arousing
unconsciousness

Diagnosis
The doctor will review your medical history and symptoms and do a physical exam.
To check for heartbeat irregularities and ischemia (lack of blood and oxygen reaching the tissues), you may need an electrocardiogram (a recording of the electrical activity of the heart).

If the doctor suspects high altitude pulmonary edema, you'll need:

blood tests to determine your white blood cell count
blood gases to determine the acid/base status of your blood
a chest X-ray to evaluate the distribution of fluid buildup
If the doctor suspects high altitude cerebral edema, additional tests may be needed. For example, the doctor may recommend a CT scan (computed tomography, a computer-generated, cross-sectional picture of internal body parts) of the head.


Treatment
When symptoms are mild and uncomplicated, descending to a lower altitude is often all that's needed. You may receive oxygen to help relieve symptoms. It's also helpful to rest, avoid alcohol and drink plenty of fluids.
If you develop high altitude pulmonary or cerebral edema, moving to a lower altitude is essential. You may also need oxygen, bedrest or other support measures. If immediate descent isn't possible, portable hyperbaric chamber therapy may be an alternative. With this treatment, you're placed in an airtight enclosure strong enough to withstand high internal pressure. When the device is inflated to two pounds per square inch, hyperbaric chamber therapy is equal to a drop in altitude of 5,000 feet. Improvement is often rapid.

In severe cases, hospitalization may be needed. Oxygen may be given through nasal prongs or artificial ventilation. You may also need bedrest, diuretics (a medication that helps the body get rid of excessive fluid buildup in the tissues and lungs), steroids and postural drainage (positioning a person so that gravity encourages drainage of lung secretions).


Complications
Altitude illness may lead to high altitude retinal hemorrhages (bleeding in the retina, the light-sensitive tissue at the back of the eye that sends nerve impulses to the brain). This rarely causes symptoms. If you develop any visual changes, however, descending to a lower altitude would be best.
If left untreated, high altitude pulmonary edema can lead to cyanosis (a slightly bluish, grayish or dark purple cast to the skin caused by low levels of hemoglobin) and respiratory distress. High altitude cerebral edema can lead to motor and sensory deficits, seizures and coma. Due to respiratory or neurological deterioration, both conditions are potentially fatal.

Chronic mountain sickness may develop if you live at high altitudes for several years. This condition is characterized by an abnormal increase of red blood cells. Symptoms include cough, shortness of breath, headache and muscle weakness. Chronic mountain sickness affects men more often than women.


Pregnancy-specific information
Pregnant women who live at high altitudes have an increased risk of high blood pressure and babies with low birth weight and high bilirubin levels. (Bilirubin is a yellow pigment formed when red blood cells die and are recycled by the body. Jaundice, a condition that causes yellowing of the skin or whites of the eyes, may develop if too much bilirubin accumulates in the blood.)
During pregnancy, traveling to high altitudes may be unsafe. Although there's not much research in this area, the Centers for Disease Control and Prevention (CDC) recommends that pregnant women avoid traveling to altitudes higher than 13,123 feet. Late in the pregnancy or at any point during a high-risk pregnancy, the limit drops to 8,200 feet. Adjusting to the decreased oxygen supply might be too demanding for both you and your baby. If the trip is unavoidable, it's important to consult your doctor before you travel for recommendations on any special care or tests you may need while you're there.


Senior-specific information
The risk of developing chronic mountain sickness increases with age. Older adults are also more likely to have chronic health conditions that could be aggravated by higher altitudes, such as heart or lung disease. If you have any health conditions, consult your doctor before travelling to high altitudes.

Prevention
To prevent altitude sickness, increase your altitude slowly. Never go to higher altitudes if you develop symptoms of altitude illness.
It may also help to drink plenty of fluids, avoid overexertion, and eat a high-carbohydrate diet. If you'll be outside, be sure to wear eyewear with UV protection and use sunscreen. Covering your nose and mouth with a porous fabric that allows you to breathe but retains warmth and moisture (such as silk) may help prevent bronchitis (inflammation of the lining of the large air passages in the lungs) and pharyngitis (inflammation of the pharynx, the passageway for air from the nasal cavity to the larynx and food from the mouth to the esophagus).

If you'll be mountain climbing, begin slowly at an altitude below 9,000 feet above sea level. Adjust to the altitude with a day of rest after arriving. Limit climbing to 1,000-foot increases per day, especially if you're above 10,000 feet. Listen to your body signals -- slow down if you're winded or tired. Avoid alcohol, sleeping pills and narcotics, all of which may aggravate symptoms of altitude illness. If possible, sleep at a lower altitude (especially if you're climbing above 12,000 feet). At higher altitudes, your blood oxygen level may drop even more during sleep. Find out if supplemental oxygen will be available at your destination, or consider bringing your own oxygen supply.

If you have a history of altitude problems or plan a rapid ascent to more than 8,000 feet above sea level, make sure you're familiar with appropriate emergency procedures. You may also want to ask your doctor about preventive medication. For example:

Acetazolamide (Diamox, for example) can be helpful when taken 24 hours before ascent and continued for two to three days at the higher altitude. (This medication is not appropriate if you're allergic to sulfa drugs.)

Dexamethasone (Decadron, for example) may reduce the odds of developing acute mountain sickness or reduce its severity. Side effects may include restlessness and exaggerated depression. When you stop taking the drug, you may develop rebound altitude illness.

Nifedipine (Procardia, for example) decreases pressure in the arteries in your lungs. It's often recommended for those who are susceptible to high altitude pulmonary edema.

Ginkgo biloba (an herbal supplement) may help prevent AMS when taken before ascent. It appears to be most effective during moderate rates of ascent. More research is planned to compare the supplement's effectiveness to traditional treatments.

Salmeterol (a type of inhaler) may help prevent HAPE. More research is needed to confirm the findings, however.
During your trip, report symptoms of altitude illness to your doctor or a local medical center -- especially if they're severe.