Climbing Kilimanjaro: The Stages of Altitude Sickness and their Treatment

• Intermediate altitude: 5000-8000ft or 1520- 2440m
• High altitude: 8000-14000ft or 2440-4270m
• Very high altitude: 14000- 18000ft or 4270- 5490m
• Extreme altitude: ≥ 18000ft or 5490m

Oxygen concentration at high altitudes is the same as oxygen concentrations at sea level, which is 21%. However, the partial pressure of oxygen decreases with decreased barometric pressure. This means that overall oxygen content is lower.

Increased ventilation is the initial response. Hypoxia is sensed by the carotid bodies, which then signal to the respiratory centers to increase respiration rate. The increase in respiration rate causes decreases in CO₂ levels, leading to a respiratory alkalosis. To compensate, the kidneys will excrete bicarbonate to normalize the body’s pH at the new increased respiratory rate. It takes the body 4-7 days to achieve ventilatory acclimation.

In short: decreased oxygen à reflex increased respiration à decreased CO₂ à respiratory alkalosis à bicarbonate diuresis à re-establish normal pH and hemostasis

Acetazolamide helps in bicarbonate diuresis, which helps re-establish normal pH at increased respiratory rate (see above explanation). One should take this before exposure to high-altitudes.

• Blood: Erythropoietin level increases causing increase in red blood cells. This process takes days to weeks to complete and is more significant for people who live at high altitudes.
• Cardiovascular: Hypoxia leads to an increase in sympathetic drive, which increases heart rate and cardiac output. Pulmonary circulation constricts in response to hypoxia leading to pulmonary hypertension. Pulmonary hypertension allows for susceptibility to pulmonary edema seen in HAPE (more below).
• CNS: Blood flow to the brain increases to allow increased oxygen delivery. This response is limited. Excessive increases in blood flow can lead to increase intracranial pressure.
• Sleep: Hypoxia is maximal during sleep. Sleeping in high altitudes can be a challenge. Stage III and IV of the sleep cycle are shortened, and more time is spent awake. People sleeping at high altitudes may also experience frequent awakenings and periodic Cheyne-Strokes respirations.

Acute mountain sickness (AMS), high-altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE) are all spectrums of high altitude syndromes caused by hypoxia. The exact pathophysiology is unclear. The mechanism is thought it be through a series of neurohumoral and hemodynapnic changes that lead to capillary leakage and edema.

• Acute Mountain Sickness: You can anticipate AMS in people who quickly ascend 6560ft or 2000M without acclimation.
  • The constellation of symptoms including fatigue, headaches, dizziness/lightheadedness, sleep disturbances, and GI disturbances. Symptoms have been likened to a bad hangover.
  • Lake Louise AMS score is used to grade severity of AMS: http://www.treksafe.com.au/medical/documents/LakeLouisescore_000.pdf
• High altitude pulmonary edema: HAPE can develop 1-4 days after rapid ascent to altitudes greater than 8000ft or 2500m. HAPE is the primary cause of high altitude-related deaths. Hypoxia causes global pulmonary vasoconstriction leading to increased pulmonary pressures. Increased pressures can damage capillary walls causing leakage of fluid and pulmonary edema.
  • Symptoms include exertional dyspnea progressing to dyspnea at rest. Signs include rales on the right mid-lung field (rales become diffuse rales as disease progresses), cough, weakness, and cyanosis.
• High altitude cerebral edema: This is the final stage of high altitude syndrome. It is caused by increased cerebra edema.
  • Early symptoms include altered mental status and ataxia. HACE can progress to focal neurological deficits and coma.

• The best treatment is prevention
  • If ascending to altitudes above 8000ft or 2500m for more than 1 day, spend at least 1 night at an intermediate altitude of 6560ft or 2000m. Allow for 2 nights at each 3230ft or 1000m gain in altitude.
  • Avoid exertion, alcohol, respiratory depressants (like sleeping medications)
  • Acetazolamide or dexamethasone
• Treatment is centered on descending and oxygen supplemental oxygen. The 3 principles of treating high altitude syndromes are:
  1. Do not go on to higher altitudes, and sleep if you are symptomatic
  2. Descend if symptoms do not improve or worsen
  3. If you notice altered mental status, ataxia, or signs or symptoms of HAPE, descend immediately