As recreational travel and activities at high elevations become more common, medical providers are seeing an increase in patients experiencing high-altitude illness or who are seeking advice before traveling to a high altitude (defined as an elevation greater than 4,921 ft [1,500 m]).1 More than 40 million tourists visit recreation areas above 7,800 ft (2,377 m) in the American West each year and many travel to Asia, Africa, and South America to elevations greater than 13,000 ft (3,962 m). More than 700,000 people live above 8,200 ft (2,499 m) in the state of Colorado.1
This shift in travel has created a need for primary care providers to know how to counsel patients who travel to high altitudes. Common medical conditions that should be considered when patients are planning high-altitude travel include pulmonary, cardiac, diabetes, and pregnancy.
Providers should be prepared to address two areas of concern when advising these patients:
- Will altitude have negative effects on the underlying medical condition?
- Will the medical condition increase the patient's risk of developing altitude illness?
ELEVATION AND ALTITUDE ILLNESS
Patients with chronic diseases who travel to high altitudes may be affected by decreased air pressure, increased ultraviolet radiation, low humidity, and cold. Hypoxia is the primary stressor. For example, at 10,000 ft (3,048 m), the inspired PaO2 is 69% of sea-level value.2 The severity of hypoxic stress depends on the elevation, rate of ascent, and duration at altitude. Latitude also is a factor because the barometric pressure changes with distance from the equator. The effect of hypoxia is greater at polar regions and is compounded by extreme cold.
High-altitude illnesses fall into three categories: acute mountain sickness, high-altitude cerebral edema, and high-altitude pulmonary edema.3
General recommendations for patients traveling to high altitudes include:
- Recognize the early symptoms of altitude illness and be willing to act.
- If experiencing symptoms, even minor, do not ascend to sleep at a higher level.
- Descend if symptoms worsen while resting at the same altitude (Table 1).4
Additional recommendations for clinical criteria, prevention, and treatment of altitude illness are in Table 2.
Patients with respiratory problems and decreased lung function (for example, from chronic obstructive pulmonary disease [COPD], pulmonary hypertension, asthma, or obstructive sleep apnea [OSA]) can face major challenges, including the potential for severe hypoxemia, when traveling to high altitudes. Although patients with lung disease may not do well in a hypoxemic environment, the healthcare provider's recommendations will vary depending on the type and severity of the patient's disease.
Patients with certain underlying medical conditions such as pulmonary circulation abnormalities and pulmonary hypertension are predisposed to high-altitude pulmonary edema and are at greater risk for altitude illness.
Pulse oximetry is a valuable diagnostic tool for evaluating patients at high altitude, as well as monitoring mountaineers traveling on expeditions. However, the device's accuracy declines when arterial oxygen saturation falls below 80%.5 Other factors affecting the accuracy of pulse oximetry readings are exposure to very cold environments, excess ambient light, shivering, cold extremities, hypovolemia, ill-fitting probes, and dark nail polish. Patients should try to minimize these factors when possible to improve measurement accuracy.
Because travel with supplemental oxygen is logistically challenging, patients may be advised to use a pulse oximeter to monitor their oxygen saturation upon arrival to a high altitude or to visit a clinic if they perceive a change in their condition. The newer portable handheld oximetry devices are recommended for greater accuracy.
Patients with COPD should be evaluated before travel because increased ventilatory requirements, inefficiency of gas exchange, and pulmonary hypertension may all develop at high altitude.
Determining which patients might require supplemental oxygen is important. Patients with predicted PaO2 less than 50 to 55 mm Hg based on a nomogram, or decreased FEV1 of 1.5 L should be cautioned about travel.6 SpO2 can be used as an indicator of who might need oxygen at altitude, or who should at least monitor their SpO2 at altitude. Neither SpO2 nor FEV1 take into account carbon dioxide retention, a sign of severe ventilatory impairment. Some studies suggest that patients who are chronically mildly hypoxemic may tolerate high altitudes better because they already are somewhat acclimatized to suboptimal oxygenation.7
Developing concrete recommendations from evidence-based medicine is challenging because of the lack of research on patients with COPD at high altitude. Tell patients on supplemental oxygen to increase the rate of flow at higher altitudes to maintain SpO2 at or above 90%. Patients can use their pulse oximeter to assess their need for oxygen and monitor their oxygen therapy. National guidelines recommend that patients with FEV1 less than 1 L should avoid travel without supplemental oxygen.8
Patients with asthma generally do better at high altitude. High-altitude treatment has been used in Europe for patients with asthma for over a century. Success of this treatment has long been attributed to the absence of house dust mite allergens at altitudes above 5,249 ft (1,600 m).9 As a result of low relative humidity and temperatures, the mountain climate is not only free of house dust mites, but also is relatively free of other airborne allergens including fungal spores and mold. Due to many months of snow cover, the pollen season is short and critical levels of pollen concentration usually are only reached a few days per year. In contrast to urban areas, the pollution levels are much lower in most alpine areas, resulting in a reduction in airway inflammation and reactivity in patients with asthma. Advantages also include enabling full lung expansion by increasing airflow and reducing respiratory resistance due to the lower air density.
In contrast, hypoxia, and hypocapnia, along with colder air temperatures and lower humidity can elicit airway reactivity. Cross-country skiers, mountaineers, and other patients who have high ventilatory demands can have a greater number of asthma exacerbations or exercise-induced bronchoconstriction.7
Patients with moderate persistent or severe asthma should avoid traveling to high-altitude areas.7 Patients who use rescue inhalers frequently (more than three times a week) before a trip to high altitude and who expect to be more physically active while at high altitude are at increased risk for exacerbations.7 Along with their albuterol rescue inhaler, patients should pack a course of corticosteroids in case of an exacerbation, with instructions on how to use them.
Patients with OSA have daytime sleepiness, cognitive impairment, and increased risk of cardiovascular disease, all of which can significantly impair quality of life. Nightly use of continuous positive airway pressure (CPAP) is the most effective therapy. Latshang and colleagues performed sleep studies in Switzerland on subjects who normally lived at an altitude below 2,625 ft (800 m) to examine changes in OSA at higher elevations (5,348 ft [1,630 m] and 8,497 ft [2,590 m]).10 Better control of OSA was achieved with a combination of the respiratory stimulant acetazolamide and auto-CPAP therapy, compared with auto-CPAP alone. Although newer CPAP devices are smaller and battery-operated, extended treks at remote mountain locations may not allow for recharging. Acetazolamide is helpful for patients with OSA who cannot use their CPAP devices in remote locations.11
The hypoxemia of high altitude triggers a number of pulmonary and cardiovascular adjustments that maintain myocardial blood flow and oxygen delivery to vital organs. Elements relevant to patients with cardiovascular disease are increased catecholamine release, increased myocardial work, and increased pulmonary artery pressure. This raises the question of whether patients with cardiovascular problems can safely venture to high altitudes.
Coronary artery disease (CAD)
Few studies have examined the effect of high altitude (particularly altitudes above 11,483 ft [3,500 m]) on patients with a history of CAD.12 Normally, coronary arteries dilate in response to hypoxemia or exercise; because coronary vasodilation is impaired in patients with CAD, high altitudes are risky. The main factor in myocardial ischemia in patients with CAD is increased myocardial oxygen demand due to increases in heart rate, myocardial contractility, and ventricular afterload. Patients are at increased risk for angina in the initial few days at high altitude, due to increased cardiac work from elevated heart rate and higher BP. However, patients who are stable at sea level generally return to preascent levels of angina threshold after 5 days of acclimatization.13 Oxygen delivery increases with ventilatory acclimatization. For this reason, patients with CAD should avoid strenuous activity until they acclimatize, particularly in cold winter temperatures. Increased sympathetic activity due to cold temperatures can aggravate ischemia.7
Contraindications for travel to high altitude include unstable CAD or a history of ischemia at low-to-moderate workloads. Unstable angina, recent myocardial infarction, or recent revascularization (within 6 months) also are considered contraindications.11 Patients with a previous myocardial infarction or history of revascularization more than 6 months ago and who do not demonstrate ischemia on stress testing have traveled to altitudes greater than 13,780 ft (4,200 m) without untoward events.12 Patients with complicated CAD should have a cardiology consultation before travel.
Patients with hypertension on ascent to high altitude exhibit slight increases in systolic BP, depending on hypoxic stress, cold, diet, exercise, and genetics. Marked variability in BP response among patients with hypertension is noted during short stays at high altitude. Patients with hypertension on ascent to high altitude exhibit modest increases in systolic BP, depending on hypoxic stress, cold, diet, exercise, and genetics. The lack of predictable response can make it difficult to advise these patients. Patients with very labile or poorly controlled hypertension should closely monitor their BP upon ascent and have a plan for urgent medical evaluation at local clinics if needed. These patients should carry small home monitors or visit clinics to check their BP, if possible. There is no evidence that hypertension increases the risk of acute mountain sickness. Limited research exists on managing these patients and determining whether changes in medical treatment are advised.
Until additional research suggests otherwise, patients should follow sea-level recommendations for medication adjustments and seek immediate medical evaluation for hypertensive urgency or emergency if they meet the following criteria:
- Systolic BP greater than 180 mm Hg or diastolic BP greater than 120 mm Hg with accompanying symptoms, such as chest pain, vision changes, shortness of breath, or altered mental status.
- Systolic BP greater than 220 mm Hg or diastolic BP greater than 140 mm Hg with no accompanying symptoms.14
No universal guidelines exist and there are few studies on patients with poorly controlled hypertension traveling to altitudes greater than 11,483 ft (3,500 m).7
Patients with well-controlled type 1 diabetes should acclimatize well to high altitude without adverse reactions. However, symptoms of altitude illness can be difficult to distinguish from those of hypoglycemia. Although these patients are not at increased risk for altitude illness, maintaining good glycemic control can pose challenges. For this reason, frequent glucose monitoring is recommended to ensure proper glycemic control. Patients should use the newer glucose dehydrogenase-based glucometers because temperature, humidity, and elevation affect the accuracy of older glucometers. The newer glucose dehydrogenase-based glucometers perform better than glucose oxidase systems because oxygen is not a factor in the reaction pathway.7
A patient's insulin requirements may change at high altitude. Literature reveals conflicting evidence for both an increase and decrease in insulin requirements. Patients may need to make adjustments based on glucose readings and in response to altitude, anorexia, exercise, illness, nausea, ketone bodies, or time zone changes.15
Patients with insulin pumps may need to decrease the basal insulin rate or switch to subcutaneous injections until they can verify insulin pump function.7 Insulin pumps may form bubbles that expand at high altitude due to decreases in ambient pressure. This can cause excess insulin administration, so patients with insulin pumps may need to decrease the basal insulin rate or switch to subcutaneous injections.7 Studies have shown that patients with type 2 diabetes can safely take part in high-altitude trekking after adequate preparation. Patients with either type of diabetes need to consider a number of factors before travel, including:
- current health status and medications
- risk assessment for travel with diabetic complications or comorbid conditions15
- possibility of altitude illness causing diabetic ketoacidosis (DKA)16
- diabetes self-management, including a glucagon kit or other means of correcting hypoglycemia.
In addition, acetazolamide, although helpful to speed acclimatization in many patients, may not be appropriate for those with diabetes and may precipitate ketoacidosis. Dexamethasone may worsen DKA and is generally not advised. Descent may be the safest alternative for a patient with DKA caused by acute mountain sickness.16
Warn patients about the increased risk of retinal hemorrhages and the need to avoid anticoagulants. Patients with severe retinopathy should avoid high-altitude travel, and all patients with diabetes should have a retinal screening if they plan to travel to an altitude greater than 13,123 ft (4,000 m).7 Aacetaminophen and nonsteroidal anti-inflammatory drugs are equally effective for acute mountain sickness symptoms, including headache.17,18 Patients with diabetes should refrain from strenuous exercise at high altitudes unless they are experienced with exercise at low altitude.7
Pregnant women will likely want to know if high-altitude travel poses a risk for them or their fetuses. Most of the research on pregnancy at high altitude is focused on residents, who have acclimatized to hypoxia, and little research exists on pregnant visitors. Travel to sleeping elevations of 9,843 ft (3,000 m) or less is considered safe and generally well tolerated during uncomplicated pregnancies.7 Low risk should be confirmed by prenatal checkup and ultrasound.
Contraindications for high-altitude travel in pregnant women include hypertension, preeclampsia, chronic lung disease, cardiac disease, impaired placental function, anemia, smoking, or intrauterine growth restriction. Risks are greater in pregnancies beyond 20 weeks.19 Brief sojourns at high altitude have not been shown to cause harm to the fetus.
Tell patients to ascend slowly and acclimatize slowly to avoid altitude illness. Patients should stay well hydrated, exercise less vigorously than at home, and minimize their level of high-altitude exposure. Pregnant women should avoid travel to remote areas far from medical centers.7 Women who are skiing, cycling, climbing, or doing other strenuous activities should take extra precautions to reduce the risk of trauma.7
Acetazolamide is not recommended during pregnancy as prophylaxis or treatment but may be considered in nonpregnant travelers. Pregnant patients should be advised to limit exercise before acclimatization to avoid acute mountain sickness. Acclimatization takes 2 to 3 days at altitudes above 8,202 ft (2,500 m).19
As more people travel to high altitude for work, vacation, and adventure, more patients will be asking providers for advice on the safety of such travel. Patients with chronic medical conditions and those who are pregnant must carefully plan ahead and consider the degree of elevation, speed of ascent, and physical demands. Most people with underlying medical conditions should not travel to elevations above 10,000 ft. Those who do should consult with a medical provider, preferably one with knowledge in high-altitude medicine. Most patients with chronic diseases can safely travel to elevations of up to 9,842 ft (3,000 m).
Because of limited research, no definitive guidelines exist for patients with chronic diseases who are traveling to high altitudes. However, recent journal articles have addressed many of these conditions and their interaction with high altitude. Advise patients to take a cautious approach, considering destination altitude, rate of ascent, and effects of hypoxia on the pathophysiology of the underlying disease. Patients experiencing severe acute mountain sickness, high-altitude cerebral edema, or high-altitude pulmonary edema should proceed to a medical center for evaluation as quickly as possible.
Preventive strategies for altitude illness include slow, graded ascent with time for acclimatization, recognizing early symptoms of altitude illness, and not ascending to a higher elevation if symptoms develop. If symptoms worsen, patients should descend to a lower altitude. Other general advice for acclimatization includes limiting or avoiding alcohol, staying well-hydrated, and restricting exercise to mild or moderate levels for a day or two.
With proper planning and precautions, many patients with preexisting medical conditions can safely participate in high-altitude adventures. The ultimate goal is to provide every patient with the best clinical advice for safe travels in the realm of thin air.
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Keywords:Copyright © 2017 American Academy of Physician Assistants
high altitude illness; travel; cerebral edema; pulmonary edema; hypoxia; acute mountain sickness