Altitude Sickness

Altitude sickness is when the body fails to acclimatise resulting in insufficient oxygen (hypoxia). This can be due to climbing to high altitude too quickly or genetic susceptibility. Breathing becomes difficult as you aren’t able to take on enough oxygen.

Risk Category: Low

People with no prior history of altitude illness and ascending to less than 9,000 ft (2,750 m)
People taking ≥2 days to arrive at 8,200–9,800 ft (2,500–3,000 m), with subsequent increases in sleeping elevation less than 1,600 ft (500 m) per day, and an extra day for acclimatization every 3,300 ft (1,000 m)
Prophylaxis Recommendations: Acetazolamide prophylaxis generally not indicated

Risk Category: Moderate

People with prior history of AMS and ascending to 8,200–9,200 ft (2,500–2,800 m) or higher in 1 day
No history of AMS and ascending to more than 9,200 ft (2,800 m) in 1 day
All people ascending more than 1,600 ft (500 m) per day (increase in sleeping elevation) at altitudes above 9,900 ft (3,000 m), but with an extra day for acclimatization every 3,300 ft (1,000 m)
Prophylaxis Recommendations: Acetazolamide prophylaxis would be beneficial and should be considered

Risk Category: High

History of AMS and ascending to more than 9,200 ft (2,800 m) in 1 day
All people with a prior history of HAPE or HACE
All people ascending to more than 11,400 ft (3,500 m) in 1 day
All people ascending more than 1,600 ft (500 m) per day (increase in sleeping elevation) above 9,800 ft (3,000 m), without extra days for acclimitisation.
Very rapid ascents (such as less than 7-day ascents of Mount Kilimanjaro)
Prophylaxis Recommendations: Acetazolamide prophylaxis strongly recommended

Abbreviations: AMS, acute mountain sickness; HACE, high-altitude cerebral edema; HAPE, high-altitude pulmonary edema.

High-Altitude Travel & Altitude Sickness - Peter H. Hackett, David R. Shlim – Centers for Disease Control & Prevention

Signs and Symptoms

Altitude sickness is divided in to 3 types:

Acute Mountain Sickness (AMS): Is the most common form of altitude sickness. Symptoms are like a hangover headache, dizziness, tiredness, weakness, nausea and occasional vomiting. AMS generally resolves with 12–48 hours of acclimatisation.
High Altitude Cerebral Edema (oedema) (HACE): Is a severe progression of AMS which can occur by itself or in conjunction with AMS and HAPE. Symptoms usually come within 12-24 hours of reaching a higher altitude. The symptoms are more severe than those with AMS but may also develop loss of coordination, difficulty walking, drowsiness, confusion, shortness of breath at rest and a cough. Someone with HACE needs immediate decent and oxygen if available.
High AltitudePulmonary Edema (oedema) (HAPE): Is a build-up of fluid in the lungs and can occur in conjunction with AMS and HACE. Symptoms begin with shortness of breath on exertion progressing eventually to shortness of breath at rest with tightness in the chest. There may be a blue tinge to the skin (cyanosis) and a persistent cough bringing up pink/white frothy sputum. Treatment for HAPE is immediate decent and oxygen if available. Nifedipine helps to reduce the chest tightness and help breathing.

Prevention of Altitude Sickness

Ascend gradually
Avoid going directly from low altitude to more than 9000 feet in 1 day
Once over 9000 feet don’t ascend more than 1600 feet per day and plan an extra day for every 3300 feet.
Avoid alcohol for the first 48 hours
Only mild exercise for the first 48 hours
Acetazolamide (Diamox) can also help to prevent Altitude Sickness.