Highlights & Basics
- High-altitude illness (HAI) encompasses acute mountain sickness, high-altitude pulmonary edema (HAPE), and high-altitude cerebral edema (HACE). These diseases typically occur in lowland residents following an ascent to high altitude.
- Although acute mountain sickness is normally a self-limiting disease, it is associated with the development of HACE.
- HAPE and cerebral edema are often fatal if left untreated.
- Descent is the most effective form of treatment for all three conditions.
- The diagnosis is usually clinical. However, the combination of a remote and hostile environment together with the potential for other medical conditions sometimes makes confirmation of the diagnosis difficult to achieve.
- New symptoms at altitude should be assumed to be those of a high-altitude illness until proven otherwise.
Quick Reference
History & Exam
Key Factors
headache
ataxia
change in mental state: for example, tired, irritable, confused, forgetful, irrational
abnormal tone, power, and reflexes
Other Factors
nausea, vomiting, and loss of appetite
fatigue and weakness
dizziness or lightheadedness
difficulty sleeping
visual disturbance
shortness of breath
cough with or without sputum
rales
peripheral edema
accentuated pulmonary second sound
pyrexia
elevated respiratory rate
elevated heart rate
low arterial oxygen saturation
cyanosis
urinary incontinence or retention
retinal hemorrhages and papilledema on fundoscopy
chest pain
cranial nerve palsies (III, IV, and VI)
visual and auditory hallucinations, seizures, tinnitus, vertigo, tremors, speech disturbance, and deafness
Diagnostics Tests
1st Tests to Order
clinical diagnosis
Other Tests to consider
arterial blood gases
chest radiography
ECG
chest ultrasound and echocardiography
WBC count
lumbar puncture
CT head
MRI head
Treatment Options
presumptive
high-altitude ascent planned
high-altitude ascent planned
with rapid ascent planned or known AMS susceptibility
with previous HAPE episode
acute
AMS
rest ± descent or simulated descent
analgesia
antiemetic
acetazolamide or hypnotic
acetazolamide or dexamethasone
descent or simulated descent
Definition
Classifications
Clinical entities
- A syndrome of nonspecific symptoms that occurs following arrival at altitudes above 2500 m (about 8200 feet). It is defined by the Lake Louise Consensus Group as the presence of headache, together with 1 or more of the following: gastrointestinal symptoms (anorexia, nausea, or vomiting), fatigue, dizziness, and lightheadedness.[2]
Vignette
Common Vignette 1
Common Vignette 2
Other Presentations
Epidemiology
Etiology
Pathophysiology
Diagnostic Approach
History
Examination
- Peripheral edema: this tends to occur in the periorbital area after sleep and around the ankles and wrists following exertion.[8]
- Rales: isolated occasional rales are sometimes audible on chest auscultation.[26]
- Pyrexia: a mild pyrexia may be present in AMS. A mean rise of 0.9°F (0.5°C) has been demonstrated in mild AMS (Lake Louise score = 3) and 2.2°F (1.2°C) in more severe cases (Lake Louise score >3).[49]
- A low arterial oxygen saturation (SaO2) and elevated heart rate: while a single resting SaO2 or heart rate recording may be of little use, a series of measurements showing a large difference between the patient and those who share the same ascent profile may help identify individuals who are acclimatizing poorly and are therefore prone to AMS.[50] [51] [52]
- Respiratory rate (RR): although HAPE can occasionally present without evidence of shortness of breath, an elevated resting respiratory rate is often a very useful early indication of the condition. In severe cases, the RR can exceed 40 breaths per minute at rest, making even the mildest exertion impossible.[53]
- Heart rate (HR): the resting HR is increased in those with HAPE. In severe cases, the resting HR can exceed 140 beats per minute; however, in most cases the HR is much lower, varying between 90 and 120 beats per minute.[53]
- Cyanosis: in the majority of cases there is clear evidence of cyanosis. This tends to affect extremities such as the fingers, toes, and facial features.[54]
- Pyrexia: low-grade pyrexia (100.4°F [38°C]) is a common feature of HAPE. This is usually higher than that seen in AMS.[49]
- Rales on auscultation: typically audible in both lung fields. These tend to be concentrated in mid and lower zones.
- Accentuated pulmonary second sound: on auscultation of the heart, an accentuated pulmonary second sound may be heard, indicating the presence of pulmonary hypertension.[55]
- Low arterial oxygen saturation (SaO2): SaO2 measurements are low in HAPE. At 4559 m (about 14,960 feet), HAPE patients have been shown to have a mean SaO2 of 48% compared with 78% in healthy individuals.[56] It is essential that SaO2 measurements of healthy, well-acclimatized individuals are used as a benchmark when interpreting these results. SaO2 measurements are often lower than expected in even the healthiest of individuals at altitude.
- Mental state assessment: in the early stages of HACE, signs can often be subtle and are therefore easily missed. At first HACE patients may appear tired, irritable, confused, forgetful, or prone to bouts of irrational behavior. Completing simple tasks may be problematic: tying shoe laces, using cutlery, or writing a diary may be a lengthy process. On questioning, sufferers may be unable to recall the time, day, date, or location. Conventional tests that assess basic arithmetic (subtracting 7 from 100) and memory (being given a name, age, and address and asked to recall at a later stage of the examination) are often useful in identifying the early stages of HACE.
- Neurologic assessment[4]
- Ataxia is common. This can be identified by observing the individual walk heel-to-toe for a short distance and complete a 180 degree turn. In severe cases, ataxia may prevent individuals from standing up or even sitting upright.
- Abnormalities in tone and power can also occur. There may be neck stiffness. Rarely, cranial nerve palsies are present and tend to involve those nerves controlling eye movement (III, IV, and VI).
- Reflexes are usually brisk and clonus is sometimes present. Extensor plantar reflexes are common.
- Evidence of urinary incontinence or retention is sometimes seen.
- Visual and auditory hallucinations, seizures, tinnitus, vertigo, tremors, speech disturbance, and deafness have been reported; however, these features are rare.[4]
- Fundoscopy: retinal hemorrhages and papilledema are common.[55]
Assessment of disease severity
- Headache: 0 = none, 1 = mild, 2 = moderate, 3 = severe and incapacitating
- Gastrointestinal symptoms: 0 = good appetite, 1 = poor appetite or nausea, 2 = moderate nausea or vomiting, 3 = severe, incapacitating nausea and vomiting
- Fatigue and/or weakness: 0 = none, 1 = mild, 2 = moderate, 3 = severe
- Dizziness or lightheadedness: 0 = none, 1 = mild, 2 = moderate, 3 = severe
- Amount of unexplained fussiness: 0 (no fussiness) to 6 (constant fussiness when awake)
- Intensity of fussiness: 0 (no fussiness) to 6 (severe fussiness when awake)
- Appetite: 0 = normal, 1 = slightly less than normal, 2 = much less than normal, 3 = vomiting or not eating
- Playfulness: 0 = normal, 1 = playing slightly less, 2 = playing much less than normal, 3 = not playing
- Ability to sleep: 0 = normal, 1 = slightly less or more than normal, 2 = much less or more than normal, 3 = not able to sleep.
- Grade1 (mild): minor symptoms with limitation of heavy effort only. Slight resting tachycardia and increased respiratory rate. No limitation of normal activities.
- Grade 2 (moderate): patient is ambulatory, but normal activities are reduced. Tachycardia and tachypnea are present. Weakness, dyspnea, and cough are evident to others. Rales may be present.
- Grade 3 (serious): symptoms are present at rest. The patient may be unable to walk and may prefer to rest. Simple tasks may be impossible. Senses may be dulled. Confusion and disorientation may be present. Tachycardia and tachypnea are present. Rales are easily heard.
- Grade 4 (severe): patient is obtunded or comatose and cannot respond logically to questions or commands. Patient is unable to sit or stand. Exhibits noisy breathing with sounds of fluid in the airways. There is marked tachycardia and tachypnea.
Investigations
- Typically reduced PaO2 and reduced or normal PaCO2
- May show respiratory alkalosis.
- Changes tend to begin in the right mid zone and eventually spread across to the left. The apices and costophrenic angles are usually spared. Although prominent pulmonary vasculature may be present, this is a common finding in anyone ascending to altitude.[58] Signs of cardiogenic pulmonary edema are usually absent. Complete resolution of pulmonary infiltrates occurs quickly following recovery.[59]Image
- Typically shows a sinus tachycardia and changes compatible with acute pulmonary hypertension. These include: right axis deviation and bundle branch block; peaked P waves in leads II, III, and aVF; and an increase in the depth of precordial S waves.[55]
- In HAPE, the presence of edema can result in the formation of "comet-tail artifacts" that are visible on ultrasound scanning. These, when assessed over 28 separate lung fields, can provide an objective assessment of pulmonary edema, and can be used to monitor the course of the disease.[57] [60] The presence of a patent foramen ovale (present in 25% of the general population) may be associated with an increasing susceptibility to HAPE.[61]
- The majority of laboratory investigations are normal in HAPE.
- In some cases a small rise in the white blood count occurs; this is due to a mild neutrophil leukocytosis.[55]
- In keeping with an increase in intracranial pressure, CT scanning can reveal compression of the ventricles and changes to the gyri and sulci present on the surface of the cerebral hemispheres.
- Performed following imaging
- An increase in intracranial pressure is often seen in HACE; in advanced cases of HACE, this can exceed normal values by up to 300 mm H2O[62]
- Cerebrospinal fluid (CSF) analysis may reveal the presence of red blood cells in severe cases, but in the vast majority of HACE patients CSF will be normal.[4]
Risk Factors
History & Exam
Tests
Differential Diagnosis
Asthma, acute exacerbation
Differentiating Signs/Symptoms
- Although the absence of common triggers such as house dust mites, pollution, and pollen may improve the symptoms of some sufferers, exercise, low humidity, and cold exposure may exacerbate the condition in others.[65]
- The presence of wheeze and diurnal variation of symptoms is rare in high-altitude pulmonary edema (HAPE).
Differentiating Tests
- Therapeutic trial with short acting beta-2 agonists should significantly improve symptoms.[25]
Community-acquired pneumonia
Differentiating Signs/Symptoms
- May be difficult to clinically differentiate.
- The presence of green or yellow sputum, rigors, and a high fever that do not resolve on descent are suggestive of pneumonia.
Differentiating Tests
- Elevated WBC and positive sputum cultures.
- CXR may demonstrate infiltration, consolidation, effusions, and cavitation.
Acute exacerbation of chronic heart failure (CHF)
Differentiating Signs/Symptoms
- While significant numbers of individuals with cardiac risk factors head to altitude, the vast majority do not.[66] It is therefore far more likely that those presenting with peripheral edema, cyanosis, tachypnea, cough, and blood-stained sputum are suffering from HAPE and should be treated accordingly.
- Pronounced right-sided heart failure (ascites, hepatomegaly, and an elevated jugular venous pressure) may help distinguish the condition from HAPE.
- Presence of a gallop rhythm or a heart murmur (will be absent in HAPE).
Differentiating Tests
- Cardiomegaly on CXR.
- ECG may demonstrate arrhythmia, ischemic ST- and T-wave changes.
- Echo shows abnormal systolic and diastolic function.
Differentiating Signs/Symptoms
- May be triggered by the demands of the high-altitude environment; therefore is often difficult to distinguish clinically from HAPE.
- Those with HAPE predominantly suffer from the effects of hypoxia; those with hyperventilation will be affected by hypocapnia, dizziness, paresthesia, and perceptual disturbances.
Differentiating Tests
- Diagnosis is clinical.
Myocardial infarction
Differentiating Signs/Symptoms
- Unlike the chest pain in HAPE, MI pain is often described as a crushing pain radiating into the neck, jaw, and arms. While this may be eased with oxygen and rest similar to HAPE, descent may have little effect upon such symptoms.
- The presence of acute mountain sickness symptoms and evidence of cough and abnormalities on chest auscultation makes a diagnosis of HAPE more likely.
Differentiating Tests
- ECG demonstrates arrhythmia or acute ischemic ST- and T-wave changes.
- Cardiac catheterization will demonstrate abnormal coronary flow.
Pulmonary embolism
Differentiating Signs/Symptoms
- In the absence of clinical signs of deep vein thrombosis (pain, swelling, and redness in an affected limb) distinguishing pulmonary embolism (PE) from HAPE is difficult in the field setting.
- In the absence of any improvement on descent or HAPE treatment, the diagnosis of HAPE will be unlikely.
Differentiating Tests
- Positive D-dimer.
- ECG changes suggestive (but not diagnostic) of PE include tachycardia, new right axis deviation, new right bundle branch block and the classical S wave in lead I, Q wave with T-wave inversion in lead III.
- Ventilation-perfusion scan demonstrates abnormality in perfusion.
- CT pulmonary angiography demonstrates the presence of thrombus in the pulmonary vessels.
Acute psychosis
Differentiating Signs/Symptoms
- Thought disorder, delusions, and sensory hallucinations are features consistent with a diagnosis of acute psychosis.
- Although high-altitude cerebral edema (HACE) tends to present with motor symptoms, visual disturbance, and changes in the level of consciousness, in some cases the condition can be confused with psychotic behavior (personality changes and episodes of bizarre behavior).
- Unlike HACE, symptoms may resolve spontaneously at altitude or persist for long periods without any evidence of physical deterioration typically seen in HACE.
- In acute psychosis treatment with dexamethasone and supplemental oxygen will be ineffective.
Differentiating Tests
- Diagnosis is clinical.
Carbon monoxide poisoning
Differentiating Signs/Symptoms
- Difficult to differentiate clinically.
- Carbon monoxide poisoning has been found to occur at altitude following prolonged exposure to gas stoves in confined areas such as snow holes or small tents.[67]
- Typically, individuals present with flu-like symptoms before eventually developing ataxia, confusion, and loss of consciousness.
Differentiating Tests
- Carboxyhemoglobin level is elevated.
Differentiating Signs/Symptoms
- Warm temperatures, prolonged periods of exertion, and limited access to clean water makes dehydration a common problem at altitude. Like acute mountain sickness, headache, nausea, dizziness, and tiredness may all occur. However, these symptoms tend to respond quickly to 1 to 2 liters of isotonic fluid. In addition, thirst, orthostatic hypotension, reduced urine output, and the presence of dry skin and mucous membranes may all help distinguish dehydration from high-altitude illness.
Differentiating Tests
- Diagnosis is clinical.
Diabetic ketoacidosis (DKA)
Differentiating Signs/Symptoms
- Known history of insulin-dependent diabetes. Recent infection or change in insulin therapy.
- The presence of polyuria, thirst, and acetone on the breath supports the diagnosis of DKA. May be precipitated by high altitude.[68]
Differentiating Tests
- Elevated glucose level.
- Ketonuria.
Differentiating Signs/Symptoms
- While exhaustion may follow a prolonged period of exertion at altitude, difficulties in sleeping, nausea, headache, and dizziness should be absent.
- Importantly, in exhausted individuals abnormal neurologic signs are absent and they should still be able to perform basic tasks such as eating, drinking, and going to the toilet.
Differentiating Tests
- Diagnosis is clinical.
Differentiating Signs/Symptoms
- Headache, nausea, and malaise of a hangover can mirror the symptoms of acute mountain sickness.
- A history of excess alcohol use, an absence of sleep disturbance, and improvement with fluids and simple analgesics supports hangover as a cause of symptoms.
Differentiating Tests
- Diagnosis is clinical.
Hypoglycemia
Differentiating Signs/Symptoms
- Neurologic changes seen following prolonged periods of hypoglycemia are easily confused with illness at high altitude.
- In the absence of blood glucose measurement, a history of palpitations, shakiness, and cold extremities may be associated with the early manifestations of a hypoglycemic attack.
- Clinical improvement following the administration of sugary foods makes acute mountain sickness unlikely.
Differentiating Tests
- Low glucose level.
Hyponatremia
Differentiating Signs/Symptoms
- Those with heat exhaustion respond to salt replacement and appropriate fluid resuscitation.
- In cases of hyponatremia caused by the intake of excessive amounts of water, fluid restriction is necessary.
Differentiating Tests
- Electrolytes abnormal, although diagnosis is clinical in field.
Hypothermia
Differentiating Signs/Symptoms
- Difficult to differentiate clinically.
- Core temperature low.
- Warming measures (hot water bottles, additional layers of dry clothing, and the consumption of warm drinks and food) will correct symptoms.
- Hypothermia can often occur in those with HAPE or HACE.
Differentiating Tests
- Diagnosis is clinical.
Ingestion of hallucinogenic agents
Differentiating Signs/Symptoms
- A wide range of hallucinogenic agents are now available in popular high-altitude destinations.
- While psychiatric symptoms predominate, changes in neurology can make it difficult to distinguish their use from HACE.
- Supplemental oxygen and other HACE treatments will have no effect.
- A thorough history from teammates and onlookers is essential.
Differentiating Tests
- Diagnosis is clinical.
Migraine
Differentiating Signs/Symptoms
- Ascent to high altitude is a recognized trigger for migraine.
- The presence of a prodrome and aura may help distinguish migraine from acute mountain sickness (AMS). Similarly, migraine headaches tend to be unilateral and pulsating and unlike AMS can be accompanied by nasal stuffiness, scalp tenderness, and changes in bowel and bladder habits.
- While migraines typically last for up to 72 hours, AMS symptoms may persist for longer and sometimes only resolve with descent.
- Unlike some migraines, AMS is not associated with menstruation and does not cause visual disturbances or unilateral motor weakness.
Differentiating Tests
- Diagnosis is clinical.
Seizures, generalized
Differentiating Signs/Symptoms
- In high-altitude cerebral edema, seizures tend to occur in the final stages of the condition and will have been preceded by other symptoms.
- At altitude, seizure activity in those with epilepsy varies between individuals. The combination of poor sleep, hypoxia, and hypocapnia has been postulated as a cause for increasing activity in some cases.[71]
- A thorough history is useful in these cases and may identify changes in the patient's medication compliance; or, in those presenting with unexpected seizures, there may be evidence of unexplained events several years before.[71]
Differentiating Tests
- MRI and EEG are confirmatory and will demonstrate epileptiform activity, and focal or localizing abnormality.
Stroke
Differentiating Signs/Symptoms
- Most commonly present with amaurosis fugax, dysphasia, and unilateral disturbances in sensory and motor function, in some cases changes in consciousness can occur that may be clinically difficult to differentiate from HACE.
- HACE is often preceded by symptoms of acute mountain sickness and improves with descent and appropriate treatment; symptoms of transient ischemic attack or stroke often persist.
Differentiating Tests
- CT head will demonstrate ischemia or hemorrhage.
Criteria
- Headache
- 0 = none
- 1 = mild
- 2 = moderate
- 3 = severe and incapacitating
- Gastrointestinal symptoms
- 0 = good appetite
- 1 = poor appetite or nausea
- 2 = moderate nausea or vomiting
- 3 = severe, incapacitating nausea and vomiting
- Fatigue and/or weakness
- 0 = none
- 1 = mild
- 2 = moderate
- 3 = severe
- Dizziness or lightheadedness
- 0 = none
- 1 = mild
- 2 = moderate
- 3 = severe
- Amount of unexplained fussiness: 0 (no fussiness) to 6 (constant fussiness when awake)
- Intensity of fussiness: 0 (no fussiness) to 6 (severe fussiness when awake)
- Appetite: 0 = normal, 1 = slightly less than normal, 2 = much less than normal, 3 = vomiting or not eating
- Playfulness: 0 = normal, 1 = playing slightly less, 2 = playing much less than normal, 3 = not playing
- Ability to sleep: 0 = normal, 1 = slightly less or more than normal, 2 = much less or more than normal, 3 = not able to sleep.
- Minor symptoms with limitation of heavy effort only. Slight resting tachycardia and increased respiratory rate. No limitation of normal activities.
- Patient is ambulatory, but normal activities are reduced. Tachycardia and tachypnea are present. Weakness, dyspnea, and cough are evident to others. Rales may be present.
- Symptoms are present at rest. The patient may be unable to walk and may prefer to rest. Simple tasks may be impossible. Senses may be dulled. Confusion and disorientation may be present. Tachycardia and tachypnea are present. Rales are easily heard.
- Patient is obtunded or comatose and cannot respond logically to questions or commands. Patient is unable to sit or stand. Exhibits noisy breathing with sounds of fluid in the airways. There is marked tachycardia and tachypnea.
Treatment Approach
Acute mountain sickness (AMS)
High-altitude pulmonary edema (HAPE)
High-altitude cerebral edema (HACE)
Treatment Options
high-altitude ascent planned
prophylactic nonpharmacologic measures
Comments
with rapid ascent planned or known AMS susceptibility
acetazolamide or dexamethasone
Primary Options
- acetazolamide
children: 2.5 mg/kg orally (immediate-release) every 12 hours, maximum 125 mg/dose; adults: 125 mg orally (immediate-release) twice daily, or 500 mg orally (extended-release) once or twice daily
- acetazolamide
Secondary Options
- dexamethasone
adults: 2 mg orally every 6 hours, or 4 mg every 6-12 hours
- dexamethasone
Comments
- Medications are usually started at least 1 day prior to ascent and continued until acclimatization is deemed to be complete. If dexamethasone is used for longer than 10 days, medication should be tapered over one week rather than stopped abruptly to avoid risk of adrenal suppression.[29]
- Dexamethasone should also not be used for prophylaxis in children due to the potential for side effects unique to this population and the availability of other safe alternatives: namely, graded ascent and acetazolamide.[29]
with previous HAPE episode
nifedipine
Primary Options
- nifedipine
children: consult specialist for guidance on dose; adults: 30 mg orally (extended-release) every 12 hours
- nifedipine
Comments
- Nifedipine has been shown to reduce the incidence of high-altitude pulmonary edema (HAPE) in individuals with a previous history of radiographically documented disease.[45] Extended-release preparations are preferred, and should be started 24 hours prior to ascent and continued until return to a low altitude.[7] [29]
AMS
rest ± descent or simulated descent
Comments
- In the event of acute mountain sickness (AMS), sufferers need to stop, rest, treat their symptoms, and descend if improvements do not occur (the STOP, REST, TREAT, DESCEND approach). In mild cases it may be enough to rest for a few days and treat symptoms with simple analgesia and antiemetics.
- Patients with AMS can resume their ascent once symptoms resolve, and it is advisable to use pharmacologic prophylaxis before continuing. Further ascent or re-ascent to a previously attained altitude must not be attempted in the presence of continuing symptoms.
- However, in those who fail to improve within 12-24 hours, descent is usually necessary and any further ascent should be made with the utmost caution. Often a descent of only a few hundred meters can improve symptoms.
- AMS can also be treated with supplemental oxygen (2-4 L/minute) and portable hyperbaric therapy. Unfortunately, their effects are short-lived and symptoms tend to return within a few hours of stopping treatment.[86]
analgesia
Primary Options
- acetaminophen
children: 10-15 mg/kg orally every 4-6 hours when required, maximum 75 mg/kg/day; adults: 325-1000 mg orally every 4-6 hours when required, maximum 4000 mg/day
- acetaminophen
Secondary Options
- ibuprofen
children ≥6 months of age: 5-10 mg/kg orally every 6-8 hours when required, maximum 40 mg/kg/day; adults: 400 mg orally every 4-6 hours when required, maximum 3200 mg/day
- ibuprofen
- aspirin
children: 10-15 mg/kg orally every 4-6 hours when required, maximum 60-80 mg/kg/day; adults: 325-650 mg orally every 4-6 hours when required, maximum 4000 mg/day
- aspirin
Comments
- Headache should be treated with analgesics. There is anecdotal evidence to suggest that a significant risk of gastrointestinal bleeding exists at altitude.[80] It is therefore recommended that aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen are used with caution at altitude.
- In a prospective randomized clinical trial with a field-based, double-blinded design, ibuprofen effectively reduced symptoms such as headaches and nausea.[87]
antiemetic
Primary Options
- prochlorperazine maleate
children: ≥2 years of age and 9-13 kg body weight: 2.5 mg orally every 12-24 hours when required, maximum 7.5 mg/day; children: ≥2 years of age and 14-17 kg body weight: 2.5 mg orally every 8-12 hours when required, maximum 10 mg/day; children: ≥2 years of age and 18-39 kg body weight: 2.5 mg orally every 8 hours or 5 mg every 12 hours when required, maximum 15 mg/day; children: ≥2 years of age and >39 kg body weight: 5 mg orally every 6-8 hours when required, maximum 20 mg/day; adults: 5-10 mg orally every 6-8 hours when required, maximum 40 mg/day
- prochlorperazine maleate
- promethazine
children ≥2 years of age: 0.25 to 1 mg/kg orally/intramuscularly/intravenously every 4-6 hours when required, maximum 25 mg/dose and 100 mg/day; adults: 12.5 to 25 mg orally/intramuscularly/intravenously, every 4-6 hours when required, maximum 100 mg/day
- promethazine
- ondansetron
children: consult specialist for guidance on dose; adults: 4-8 mg orally/intravenously every 8 hours when required, maximum 24 mg/day
- ondansetron
- metoclopramide
children: consult specialist for guidance on dose; adults: 5-10 mg orally/intramuscularly/intravenously every 6-8 hours when required, maximum 45 mg/day
- metoclopramide
Comments
- Antiemetics can be used to treat symptoms of nausea and vomiting.
- Metoclopramide was found to be effective at reducing symptoms, including headache and nausea, in a prospective, double-blinded, randomized, field-based clinical trial.[87]
acetazolamide or hypnotic
Primary Options
- acetazolamide
children: 2.5 mg/kg orally (immediate-release) every 12 hours, maximum 250 mg/dose; adults: 250 mg orally (immediate-release) every 12 hours
- acetazolamide
- temazepam
adults: 10 mg orally once daily at night
- temazepam
- zolpidem
adults: 5 mg orally (immediate-release) once daily at bedtime when required; 6.25 mg orally (extended-release) once daily at bedtime when required; higher doses may cause next-morning drowsiness and are not recommended, especially in women
- zolpidem
Comments
- Acetazolamide or a hypnotic may be used to treat sleep disturbances.
- Acetazolamide is often used to successfully treat episodes of periodic breathing that are commonly seen during sleep at altitude.[88]
acetazolamide or dexamethasone
Primary Options
- acetazolamide
children: 2.5 mg/kg orally (immediate-release) every 12 hours, maximum 250 mg/dose; adults: 250 mg orally (immediate-release) every 12 hours
- acetazolamide
- dexamethasone
children: 0.15 mg/kg orally every 6 hours, maximum 4 mg/dose; adults: 8 mg orally initially, followed by 4 mg every 6 hours
- dexamethasone
- dexamethasone sodium phosphate
children: 0.15 mg/kg intramuscularly/intravenously every 6 hours, maximum 4 mg/dose; adults: 8 mg intramuscularly/intravenously initially, followed by 4 mg every 6 hours
- dexamethasone sodium phosphate
Comments
descent or simulated descent
Comments
- In those who fail to improve within 12-24 hours, descent is usually necessary. Often a descent of only a few hundred metres can improve symptoms.
- AMS can also be treated with supplemental oxygen (2-4 L/min) and portable hyperbaric therapy. Unfortunately, their effects are short-lived and symptoms tend to return within a few hours of stopping treatment.[86]
HAPE only
descent or simulated descent
Comments
- Ideally, those with high-altitude pulmonary edema (HAPE) should descend quickly to low altitude.
- In the event of any delay, the partial pressure of inspired oxygen (PIO2) can be increased by using supplemental oxygen (face mask or nasal prongs 2-4 L/minute), or a portable hyperbaric chamber (2 psi - 13.8 KPa).[7]
- A combination of supplemental oxygen and portable hyperbaric treatment can be used in severe cases.[91]
nifedipine
Primary Options
- nifedipine
children: consult specialist for guidance on dose; adults: 30 mg orally (extended-release) every 12 hours
- nifedipine
Comments
HACE only
descent or simulated descent
Comments
- Ideally, those with high-altitude cerebral edema (HACE) should descend quickly to low altitude.
- In the event of any delay, the partial pressure of inspired oxygen (PIO2) can be increased by using supplemental oxygen (face mask or nasal prongs 2-4 L/minute), or a portable hyperbaric chamber (2 psi - 13.8 KPa).[7]
- A combination of supplemental oxygen and portable hyperbaric treatment can be used in severe cases.[91]
dexamethasone
Primary Options
- dexamethasone
children: 0.15 mg/kg orally every 6 hours, maximum 4 mg/dose; adults: 8 mg orally initially, followed by 4 mg every 6 hours
- dexamethasone
- dexamethasone sodium phosphate
children: 0.15 mg/kg intramuscularly/intravenously every 6 hours, maximum 4 mg/dose; adults: 8 mg intramuscularly/intravenously initially, followed by 4 mg every 6 hours
- dexamethasone sodium phosphate
Comments
concurrent HAPE and HACE
descent or simulated descent
Comments
- Those with concurrent high-altitude pulmonary edema (HAPE) and high-altitude cerebral edema (HACE) should descend quickly to low altitude.
- In the event of any delay, the partial pressure of inspired oxygen (PIO2) can be increased by using supplemental oxygen (face mask or nasal prongs 2-4 L/minute), or a portable hyperbaric chamber (2 psi - 13.8 KPa).[7]
- A combination of supplemental oxygen and portable hyperbaric treatment can be used in severe cases.[91]
nifedipine + dexamethasone
Primary Options
- nifedipine
children: consult specialist for guidance on dose; adults: 30 mg orally (extended-release) every 12 hours
AND
- dexamethasone
children: 0.15 mg/kg orally every 6 hours, maximum 4 mg/dose; adults: 8 mg orally initially, followed by 4 mg every 6 hours
or
- dexamethasone sodium phosphate
children: 0.15 mg/kg intramuscularly/intravenously every 6 hours, maximum 4 mg/dose; adults: 8 mg intramuscularly/intravenously initially, followed by 4 mg every 6 hours
- nifedipine
Comments
- Patients require treatment with both nifedipine and dexamethasone.
- Nifedipine is able to inhibit hypoxic pulmonary vasoconstriction and reduce pulmonary artery pressure.[3] It can therefore be used in both prophylaxis and treatment of high-altitude pulmonary edema (HAPE).[57] [92] Care should be taken to avoid excessively large decreases in systemic pressure as this may decrease cerebral perfusion pressure and cause cerebral ischemia.
- In high-altitude cerebral edema (HACE), dexamethasone often improves the clinical situation and makes evacuation easier.
Emerging Tx
Phosphodiesterase-5 inhibitors for HAPE prophylaxis
Dexamethasone for HAPE prophylaxis
Ginkgo biloba for acute mountain sickness (AMS) prophylaxis
Prevention
Primary Prevention
Follow-Up Overview
Prognosis
Monitoring
Complications
Citations
Centers for Disease Control and Prevention. CDC Yellow Book 2024: health information for international travel. Section 4: environmental hazards & risks - high elevation travel & altitude illness. May 2023 [internet publication].[Full Text]
Roach RC, Hackett PH, Oelz O, et al. The 2018 lake louise acute mountain sickness score. High Alt Med Biol. 2018 Mar;19(1):4-6.[Abstract][Full Text]
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Key Articles
Referenced Articles
Guidelines
Diagnostic
Treatment
Summary
This guidance includes risk categories for acute mountain sickness and advice on acclimatization.Published by
Centers for Disease Control and Prevention
Published
2023
Summary
Evidence-based guidelines on the prevention and treatment of acute mountain sickness, high-altitude cerebral edema, and high-altitude pulmonary edema.Published by
Wilderness Medical Society
Published
2019