High Altitude Means Above 8000 Feet




Ed Forkos, MD



High altitude means above 8000 feet.

Certain physiologic changes will occur:

  • Increased ventilation, rate and volume
  • Periodic breathing during sleep
  • Insomnia, vivid dreams
  • Fluid retention with edema of hands and face
  • Nocturnal diuresis

All issues are a consequence of hypoxia. The human body can adapt but has it’s limits. Acclimitization takes time. Variables:

  • Rate of ascent
  • (Sleep) altitude achieved
  • Time spent at elevation/”zone of tolerance”
  • Level of exertion
  • Recent altitude history
  • Past altitude history
  • Genetics

Barometric pressure drops with increasing latitude, decreasing temperature, or with weather change.

Above 5000 feet, V O2max decreases by 3% per 1000 feet. V max varies greatly between people and is genetic.


Recommendations for a safe ascent to promote acclimatization:

  • Initial 2 nights between 8000 and 10000 feet
  • 1000-1500 feet per night above 10000 feet
  • Spend 1 extra night every 3000 feet
  • Pre-trip hypoxic exposures in month before trip
  • Day hikes to higher elevation during the trip
  • No further acclimatization can occur above 23000 feet…the death zone. No drugs will help the process
  • Avoid CNS depressants that blunt ventilatory drive ie. alcohol, sedative/tranquilizers, narcotics

The acclimatization process varies greatly from person to person but is consistent for a given person. This adaptation is lost within 1 month of descent, starting within a few days.

People can, and usually do have more than one altitude-related problem. And they show up with unrelated complicating pre-exisiting conditions.

Most trips ascend too rapidly and endanger participants.



AMS Headache plus at least one of:

  • Nausea, vomiting, loss of appetite
  • Fatigue or weakness
  • Dizziness or lightheadedness
  • Sleep disturbance

HACE Progression of AMS symptoms plus:

  • Mental status change and/or ataxia (tandem gait test)
  • Absent clearcut AMS, mental status change and ataxia

HAPE Symptoms, at least 2:

  • Dyspnea at rest
  • Cough
  • Weakness/impaired exercise performance
  • Chest tightness/congestion

Signs, at least 2:

  • Crackles/wheezing one or both lungs
  • Central cyanosis. Pulse oximetry helpful as guide.
  • Rapid breathing
  • Rapid pulse
  • Modest fever (author’s addition)

Acute Mountain Sickness (AMS)

The brain is subject to a continuum of dysfunction depending upon the degree of edema/increased intracranial pressure and the rapidity of it’s development. The exact cause remains unclear but increased blood flow, decreased venous return, increased permeability of small vessels all play a role.

Depending upon the study, overall, 40-60 % will have AMS. Though usually mild and intrinsically benign, it can progress, sometimes rapidly, to full-blown HACE.

Distinguish from dehydration headache which is common, and responds to a 1 liter fluid challenge plus non-narcotic analgetic.

Distinguish from persons usual migraine.

With rest at that elevation it takes 6-48 hours to resolve.


  • Rest
  • Non-narcotic analgetic
  • Acetazolimide (Diamox), a respiratory stimulant, at 125-250 mg (latter if over 100 kg.) BID, continuing for 2-3 days at maximum attained altitude. Very safe and effective. No rebound symptoms when terminated.
  • Dexamethasone (Decadron) a potent corticosteroid, 4 mg. PO or IM, 2 doses 6 hours apart. Safe, effective, but doesn’t speed acclimatization, so rest 1-2 days at that altitude needed. If overused, can have vicious rebound brain swelling when stopped. Response can be used to “prove” AMS is cause of symptoms.
  • Mild sleeping aids including Benadryl 50-100 mg, Ambien or Lunesta.
  • Phenergan 25-50 mg. PO or PR for nausea/vomiting.
  • O2 0.5-1.0 L./min. nasal cannula during sleep. A trial of oxygen at 2-4 L./min. for several hours can also help establish AMS as cause of symptoms.
  • Descent 1000-1500 feet.


  • Proper ascent protocol
  • Diamox, used as above
  • Gingko biloba 100 mg.BID starting 5 days before
  • Ibuprofen 600 mg. every 8 hours
  • Prior CPAP use must be continued
  • Decadron 4 mg. PO before summiting


The further progression of brain swelling in the face of ongoing or worsening hypoxia. It usually takes ½ to 3 days to develop but can precipitate within several hours, so mishandling AMS is usually the cause. Hypoventilation during sleep is a common scenario; ie. the person fails to wake up in the morning! Can be seen in up to 20% of HAPE victims.

With proper caution and action this is PREVENTABLE.


  • Emergency descent to level where person slept free of symptoms, or hyperbaric bag. Logistics are problematic.
  • Dexamethasone 8 mg. stat, then 4 mg. every 6 hours as needed, orally or IM.
  • Oxygen 4 L/min. Consider air drop of canisters.
  • Potent diuretic, though discouraged because of risk of vascular collapse, can be considered in desperation: furosemide 40-80 mg. IV, or bumetanide 1-2 mg. IV
  • Descent to safety/home since the brain dysfunction takes up to weeks to clear. The hyperbaric bag only buys you time. Longterm prognosis is usually good, and person can climb again in future (with assist of Diamox.)



A diffuse but patchy vascular hyper-reactivity in response to hypoxia leading to ventilation-perfusion mismatch and patchy pulmonary edema. There is also a blunted central respiratory response to hypoxia. The result is a downward spiral in arterial oxygen level, elevated pulmonary arterial pressure with right heart strain, and exacerbation of other hypoxia-related issues like HACE. This is genetically determined, more prevalent in the young, in males, made worse by underlying cardiopulmonary pathology and respiratory infection. Severity is along a wide continuum. Onset can be precipitous. It’s probably the most common medical cause of death at altitude.


  • Emergency descent or hyperbaric bag.
  • Oxygen, high flow, to achieve O2 sat. of 99%. PEEP.
  • Nifedipine, a 10 mg. capsule punctured and swallowed, then 10 mg. every 4 hours as needed. Drugs play only a minor role here.
  • Bedrest but with upper body elevated.
  • Potent diuretics play no role and will threaten circulatory stability.
  • Once improved, the person may cautiously attempt reascent.


  • Proper graded ascent, graded increase in exercise level
  • Nifedipine sustained release, 30-90 mg. daily in 1 or2 doses. Trial of tolerability before trip.
  • PDE-5 inhibitors. Not as widely effective, but safe. Tadalafil 10 mg. BID is more often recommended but sildenafil 50 mg. every 8 hours is acceptable.
  • Beta-agonist inhaler. Very promising recent data on salmeterol.

The reality of high altitude medicine is that accurate diagnosis is treacherous and effective treatment has numerous hurdles. A recent review of 57 consecutive cases of HAPE secondarily treated in Pheriche (Nepal) revealed numerous errors! My experience is that very few doctors are skilled enough to provide this care. They should have extensive experience in emergency or intensive care medicine as well as possess a solid knowledge of high altitude medicine. BEWARE.


  1. IFAM, altitudemedicine.org, Dr. Peter Hackett’s website. Peter a principal leader in this field.
  2. CDC.gov/travel/yellowbook, excellent and up-to-date
  3. ISMM.org, for a more European perspective
  4. Wikipedia. It’s a great source for detailed, timely info, though not as carefully peer-reviewed
  5. PubMed, from the National Library of Medicine/NIH. ncbi.nlm.gov. An open source to all medical literature existing through Medline. For most studies, you can get an abstract. For many, you can see a full text copy, or be linked to a source to purchase it. There are also monographs on numerous topics.
  6. Up-to-date.com, a public sector/consumer version of a very well established, very reliable set of monographs.
  7. Beware of the numerous advice-oriented websites on health as they are not as academically rigorous.