Altitude related disorders

There are three main types of altitude-related disorders: acute mountain sickness (AMS), which may progress to high altitude pulmonary oedema (HAPE) or high altitude cerebral oedema (HACE). All three conditions are due to the chronic hypobaric hypoxia which develops at high altitudes

• headache
• nausea
• fatigue

• the risk of AMS may actually be positively correlated to physical fitness
• gain altitude at no more than 500 m per day
• acetazolamide (a carbonic anhydrase inhibitor) is widely used to prevent AMS and has a supporting evidence base
• it causes a primary metabolic acidosis and compensatory respiratory alkalosis which increases respiratory rate and improves oxygenation
• treatment: descent

• HAPE
• mechanism: hypobaric hypoxia --> uneven hypoxic pulmonary vasoconstriction --> uneven blood flow in the lungs --> areas of the lung receiving more blood experience an increase in capillary pressure --> more fluid leakage. Hypoxia may also directly increase capillary permeability, exacerbating fluid leakage into the alveolar space.
• presents with classical pulmonary oedema features
• HACE
• in contrast to the above, cerebral vasodilation is the problem. Hypoxia --> cerebral vasodilation --> elevated cerebral blood volume
• also, hypoxia --> increase in the permeability of the blood-brain barrier --> capillaries in the brain more leaky --> leading to fluid accumulation in the extracellular spaces
• both these factors --> cerebral oedema
• presents with headache, ataxia, papilloedema

• descent
• dexamethasone

• descent
• nifedipine, dexamethasone, acetazolamide, phosphodiesterase type V inhibitors*
• oxygen if available

*the relative merits of these different treatments has only been studied in small trials. All seem to work by reducing systolic pulmonary artery pressure