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🌟 Altitude-related disorders

 🎯 Pathology​

  • the partial pressure of oxygen decreases at high altitudes —> hypoxia

  • peripheral chemoreceptors are stimulated (due to hypoxia) —> increased rate and depth of breathing —> respiratory alkalosis as too much CO2 is blown off —> reduced respiratory drive

 💡 Types​

  • acute mountain sickness (AMS)

  • high altitude cerebral oedema (HACE)

  • high altitude pulmonary oedema (HAPE)

🩺 Acute mountain sickness​

  • pathology

    • self-limiting, and it’s due to the body’s reaction to the reduced partial pressure of oxygen in the atmosphere which leads to hypoxia

  • clinical features

    • mainly headache

    • nausea, vomiting, loss of appetite, fatigue

  • diagnosis

    • clinical

  • prevention

    • ascend slowly (max 500 m/day) —> to give the body enough time to adjust physiologically to the reduced partial pressure of oxygen

    • acetazolamide —> carbonic anhydrase inhibitor that speeds up the acclimatisation process by inducing a metabolic acidosis which helps increase the respiratory drive

    • descend if symptoms persist

🩺 High altitude cerebral oedema​

  • pathology

    • life-threatening complication associated with high altitudes

    • occurs 2 days above altitudes > 4000 m

  • pathophysiology

    • hypoxia —> reduced ATP in neurons and glia —> reduced activity of Na+/K+/ATPase pumps —> high Na+ in neurons —> water enters by osmosis —> neurons swell —> raised intracranial pressure —> compression of cerebral vasculature —> reduced blood supply to neurons —> death of neurons by apoptosis

  • clinical features

    • earliest clinical finding = ataxia

    • headache, papilloedema, focal neurological deficits, seizures

  • diagnosis

    • clinical

  • management

    • descent with assistance (at least 1000 m or until symptoms improve) to keep physical exertion to a minimum

    • dexamethasone

    • portable hyperbaric chamber or supplemental oxygen if descent is not an option

🩺 High altitude cerebral oedema​

  • pathology

    • most common cause of death associated with high altitudes

    • affects un-acclimatised people at altitudes between 2500-3000 m

    • non-cardiogenic

  • pathophysiology

    • hypoxia —> reduced production of nitric oxide in the pulmonary circulation —> pulmonary hypertension —> increased capillary hydrostatic pressure —> pulmonary oedema

  • clinical features

    • early

      • non-productive cough

      • exertional dyspnoea

    • later

      • dyspnoea at rest

      • orthopnoea

      • pink frothy sputum

  • diagnosis

    • clinical

  • prevention

    • slow ascent

  • management

    • supplemental oxygen or hyperbaric chamber

    • nifedipine

⛰ Mechanisms of acclimatisation

  • Metabolic acidosis

    • the initial increased hypoxic drive increases the rate and depth of ventilation leading to respiratory alkalosis as a result

    • the kidneys compensate for this by increasing the excretion of bicarbonate leading to a metabolic acidosis

  • Increased erythropoiesis

    • hypoxia increases the production of erythropoietin to speed up the maturation of red blood cells, thereby increasing the oxygen-carrying capacity of the blood

    • although a high plasma viscosity increases pulmonary vascular resistance

  • Reduced pulmonary vascular resistance

    • due to collateral circulations opening up between pulmonary arteries and veins

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