Effects of High Altitude on Pre-existing Conditions

People with pre-existing conditions should carefully evaluate risks.  Depending upon where they are traveling, medical care may be 24-48 hours away, and this delay in treatment could increase risk of death in some conditions.

Cardiovascular disease
Evidence indicates that traveling to high altitude alone does not increase the risk of heart attack. Most people with well controlled hypertension or managed chronic heart disease can travel safely to high altitude. However, acute hypoxia does increase cardiac workload, therefore people with acquired or congenital cardiovascular disease, should be medically evaluated prior to ascent. Patients with angina who are symptomatic at sea level should be cautioned that their symptoms may worsen at altitude. Medication regimens should be adjusted to reflect altered cardiac workload and drug clearance. Likewise, patients should be instructed to avoid substances that decrease ventilation or cardiac output.

Pregnancy
There is little information that identifies high altitude as a risk to pregnancy, but it is generally recommended that pregnant women avoid elevations above 12,000 feet.  There are many considerations related to pregnancy. 

The first trimester is the time when most spontaneous abortions occur. Incidence of premature delivery increase during the third trimester. A pregnant woman needs to consider her physical condition as well as the medical facilities that will be available. Travel in isolated areas, may limit access to life saving medical care for mother and neonate. It may be safer to ascend in Colorado, for example, where there are modern hospitals available than in Nepal, where access to advanced perinatal care may be unavailable.  

Diabetes
Stable diabetics can travel to higher elevations if they carefully monitor their condition and very carefully plan to manage their diabetes. Travelers should be aware that metabolic activity is often increased and caloric intake is often reduced during extended high altitude travel. Both fat and non-fat body mass is often lost during extended high altitude exposure. Euglycemic control can be very challenging. Severe ketoacidosis can occur at high altitude for reasons that are not clear, and there have been reports of people dying from ketoacidosis at high altitude. 

Exercise increases uptake of glucose and decreases the dose for exogenous insulin required. However, type I diabetics may be at risk for stress-induced hyperglycemia due to elevated catecholamine levels normally associated with acute hypobaric hypoxemia. Prudent diabetic trekkers and climbers will pack plenty of fluids, glucose supplements, medications, testing supplies and perhaps partner with someone who can do on-trail testing and treatment in the event of insulin overdose or ketoacidosis. Patient education should include the fact that insulin must not be allowed to freeze. 

Hematological problems
People with sickle cell trait should avoid high altitude. Even moderate altitude can trigger a sickle cell crisis.  A number of instances of sickling at altitude indicate an increased risk of splenic infarct.

Anemia can predispose to severe hypoxia at high altitude. Conversely, polycythemia effectively improves the oxygen carrying capacity but it can increase the risk of blood clots and embolism.

Neurological disorders
High elevations appear to lower the threshold for seizures in those with epilepsy and has triggered seizures in people with undiagnosed seizure disorders.  Within a few hours, people with brain tumors may develop severe neurologic symptoms at high elevations.  These symptoms persist even after descent.  This suggests that anyone suffering persistent neurological symptoms after descent and treatment should have a brain scan to rule out a tumor.  For reasons that aren't clear, a few people have suffered subarachnoid hemorrhages at higher elevations.

Pulmonary disorders
People with a significant degree of chronic obstructive pulmonary disease (COPD) or pulmonary hypertension will not do well at high elevations.  Asthmatics usually do well at higher elevations, possibly because of a reduction in  allergens, but should keep medications close at hand.

Vision problems
Some people who have had incisional radial keratotomy (a procedure performed from the late 1970’s to the early 1990’s) may develop acute farsightedness from higher elevations.

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