11 DESCRIPTION
AMS symptoms are like those of an alcohol hangover; headache is the cardinal symptom, usually accompanied by ≥1 of the following: anorexia, dizziness, fatigue, nausea, or, occasionally, vomiting. Symptom onset is usually 2–12 hours after initial arrival at a high altitude or after ascent to a higher elevation and often during or after the first night. Preverbal children with AMS can develop loss of appetite, irritability, and pallor.
8.7 Hepatic Impairment
The traveler should carry over-the-counter analgesics for headache and have acetazolamide to speed acclimatization as necessary or to treat early AMS. Medium risk: Acetazolamide prophylaxis would be beneficial; consider its use. Have the traveler carry acetazolamide for prevention or treatment of AMS and consider prescribing dexamethasone for emergency use. High risk: Strongly encourage acetazolamide prophylaxis, and have the traveler carry dexamethasone for emergency use. Some common high-altitude destinations require rapid ascent by airplane to >11,150 ft (>3,400 m), placing travelers in a high-risk category for AMS.
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A common travel medicine question is whether to recommend acetazolamide for travelers when gradual or staged acclimatization is not feasible. With rates of altitude illness approaching 50% in these situations, a low threshold for chemoprophylaxis is advised. In some cases (e.g., Cusco and La Paz), travelers can descend to elevations lower than the airport to sleep for 1–2 nights and then begin their ascent, perhaps obviating the need for medication. Itineraries along some trekking routes in Nepal, particularly Everest base camp, push the limits of many people's ability to acclimatize. Even on standard acclimatization schedules, the prevalence of altitude illness can approach 30% at higher elevations. AMS generally resolves within 12–48 hours if travelers do not ascend farther.
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The condition is typically self-limited, developing and resolving over 1–3 days.
Mechanism of action
A traveler's sex plays a minimal role, if any, in determining predisposition. Children are as susceptible as adults; people aged >50 years have slightly less risk. Any unacclimatized traveler proceeding to a sleeping altitude of ≥2,450 m (≥8,000 ft)—and sometimes lower—is at risk for altitude illness. In addition, travelers who have successfully adjusted to an altitude are at risk when moving to higher sleeping altitudes, especially if the altitude gain is 600–900 m (>2,000–3,000 ft). How a traveler previously responded to high altitude is the most reliable guide for future trips but only if the altitude and rate of ascent are similar, and even then, this is not an infallible predictor.
Typical dosages
In addition to inherent susceptibilities, a traveler's risk for developing altitude illness is influenced by 2 other main factors: altitude of entry to high altitude and the subsequent rate of ascent (Table 3.5.1). Creating an itinerary to avoid any occurrence of altitude illness is difficult because of variations in individual susceptibility as well as in starting points and terrain. The goal for the traveler might not be to avoid all symptoms of altitude illness but to have no more than sildenafil 45 mg chewable tablets mild illness, thereby avoiding itinerary changes or the need for medical assistance or evacuation. *Assumes starting altitude <1,200 m (<4,000 ft) Abbreviations: HACE, high-altitude cerebral edema; HAPE, high-altitude pulmonary edema; AMS, acute mountain sickness. Recommendations for each category in Table 3.5.1 are as follows: Low risk: Acetazolamide prophylaxis is not indicated. Symptoms starting after 3 days of arrival at high altitude and without further ascent should not be attributed to AMS. AMS has no characteristic physical findings; pulse oximetry is usually within the normal range for the altitude or slightly lower than normal, while a high arterial oxygen saturation (SpO2) for the altitude seems to be protective of AMS.
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- The dosage can vary depending on the condition.
- It’s important to maintain open communication with your doctor.
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- Avoid driving if you experience dizziness or vision problems.
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- Do not share medication with others.
- Regular medical check-ups are recommended during use.
With pulse oximeters available for under $30, travelers may want to have a pulse oximeter with them to gauge their acclimatization progress.
6.2 Post-marketing Experience
Increased red cell production does not play a role in acute acclimatization, although a decrease in plasma volume over the first few days does increase hemoglobin concentration. Altitude illness can develop before the acute acclimatization process is complete, but not afterward. In addition to preventing altitude illness, acclimatization improves sleep, increases comfort and sense of well-being, and improves submaximal endurance; maximal exercise performance at high altitude will always be reduced compared to that at low altitude. Travelers can optimize acclimatization by adjusting their itineraries to avoid going "too high too fast" (Box 3.5.1). Gradually ascending to altitude or staging the ascent provides crucial time for the body to adjust.
Less common
For example, acclimatizing for a minimum of 2–3 nights at around 2,450 to approximately 2,750 m (8,000–9,000 ft) before proceeding to a higher altitude is markedly protective against acute mountain sickness (AMS). The Wilderness Medical Society recommends avoiding ascent to a sleeping altitude of 2,750 m (≥9,000 ft) in a single day; ascending at a rate of no greater than 500 m (1,650 ft) per night in sleeping altitude once above 3,000 m (9,800 ft); and allowing an extra night to acclimatize for every 1,000 m (3,300 ft) of sleeping altitude gain. These reasonable recommendations can still be too fast for some travelers and too slow for others. Susceptibility and resistance to altitude illness are, in part, genetically determined traits, but there are no simple screening tests to predict risk. Training and physical fitness do not affect risk. Figure 3.5.1 shows the expected range of SpO2 for a given altitude. The differential diagnosis of AMS is broad; common considerations include alcohol hangover, carbon monoxide poisoning, dehydration, drug intoxication, exhaustion, hyponatremia, and migraine.
5.7 Priapism
Whenever possible, adding extra days to the trek can make for a more enjoyable and safer trip. Altitude illness is divided into three syndromes: AMS; high-altitude cerebral edema (HACE); and high-altitude pulmonary edema (HAPE). Some healthcare professionals consider high-altitude headache a separate entity because isolated headache can occur without the combined symptoms that define AMS. AMS is the most common form of altitude illness, affecting, for example, 25% of all visitors sleeping at altitudes >2,450 m (>8,000 ft) in Colorado. Diagnosis of AMS is based on a history of recent ascent to high altitude and the presence of subjective symptoms. Unlike viral syndromes, there is no coryza, fever, chills, or myalgia. Travelers with AMS will improve rapidly with descent ≥300 m (≥1,000 ft), and this can be a useful indication for a diagnosis of AMS. Conversions: 1,500 m = ~4,900 ft; 2,500 m = ~8,200 ft; 3,500 m = ~11,500 ft; 4,500 m = ~14,750 ft; 5,500 m = ~18,000 ft AMS improves rapidly with a descent of 300 m (1,000 ft) or more, especially if exertion is minimal.
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.. Efficacy of tadalafil for the treatment of erectile dysfunction at 24 and 36 hours after dosing: a randomized controlled trial Colorado ski resorts such as Vail and Breckenridge, with lodgings at 2,480 and 2,925 m (8,150 and 9,600 ft), respectively Cusco, Peru (approximately 3,350 m; 11,000 ft) La Paz, Bolivia (approximately 3,650 m; 12,000 ft) Lhasa, Tibet Autonomous Region (approximately 3,700 m; 12,100 ft) Everest base camp, Nepal (approximately 5,400 m; 17,700 ft) Mount Kilimanjaro, Tanzania (approximately 5,900 m; 19,341 ft) High-altitude environments expose travelers to cold, low humidity, increased ultraviolet radiation, and decreased air pressure, all of which can cause health problems. The biggest concern, however, is hypoxia, due to the decreased partial pressure of oxygen (PO2). At around 3,050 m (approximately 10,000 ft), for example, the inspired PO2 is only 69% of that at sea level; acute exposure to this reduced PO2 can lower arterial oxygen saturation to 88–91%. The magnitude and consequences of hypoxic stress depend on the altitude, rate of ascent, and duration of exposure; host genetic factors may also contribute.
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Hypoxemia is greatest during sleep; day trips to high-altitude destinations with an evening return to a lower altitude are much less stressful on the body. Because of the key role of increased ventilation on ascent to high altitudes, travelers with compromised lung function must be cautious, and all travelers should avoid taking respiratory depressants. The human body can adjust to moderate hypoxia at altitudes up to approximately 5,200 m (≤17,000 ft) but requires time to do so. Some acclimatization to high altitude continues for weeks to months, but the acute process, which occurs over the first 3–5 days following ascent, is crucial for travelers. The acute phase is associated with a steady increase in ventilation, improved oxygenation, and changes in cerebral blood flow. If staying at the altitude of onset, supplemental oxygen at 1–2 L per minute will improve headache within about 30 minutes and resolve other AMS symptoms over hours, although it is rarely available. The popular small, handheld cans of compressed oxygen can provide brief relief but contain too little oxygen (5 L at most) for sustained improvement. Travelers with AMS but without HACE or HAPE (both described below) can remain safely at their current altitude and self-treat with non-opiate analgesics (e.g., ibuprofen 600 mg or acetaminophen 500 mg every 8 hours) and antiemetics (e.g., ondansetron 4 mg orally disintegrating tablets). Acetazolamide speeds acclimatization and resolves AMS but is more commonly used and better validated for use as prophylaxis. Dexamethasone is more effective than acetazolamide at rapidly relieving the symptoms of moderate to severe AMS. If symptoms worsen while the traveler is at the same altitude and despite treatment, descent is mandatory.
| Side Effect | Frequency | Severity | Description |
|---|---|---|---|
| Headache | Common | Mild | Throbbing headache |
| Flushing | Common | Mild | Skin redness, warmth |
| Nasal Congestion | Common | Mild | Stuffy nose |
| Visual Disturbances | Less common | Mild | Blurred vision, blue tint |
| Dizziness | Less common | Mild | Feeling lightheaded |
As an encephalopathy, HACE is considered "end-stage" AMS. Fortunately, HACE is rare, especially at elevations <4,300 m (<14,000 ft).
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