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Related Subjects: |Assessing Breathlessness |Respiratory failure |Caisson Disease - Decompression sickness |Altitude sickness / Acute Mountain sickness

Altitude Sickness, also known as Acute Mountain Sickness (AMS), is a condition that can affect individuals who ascend to high altitudes, typically above 8,000 feet (2,500 meters), too quickly. The complications of high altitude are acute mountain sickness, high altitude pulmonary oedema and high-altitude cerebral oedema. Management is stop ascending and allow time for acclimatization, rest and Hydration.

About

• Rapid ascent to high altitude > 2500 m
• Increasing altitude leads to hypoxia and pulmonary vasoconstriction
• There is hypocarbia and alkalosis
• Severest form has pulmonary and cerebral oedema

Geography

• Ben Nevis Highest in UK is 1345 m so not seen
• Matterhorn 4478 m
• Mont Blanc is 4807 m
• Kilimanjaro 5895 m
• Everest 8848 m

Aetiology

• The underlying physiological process that leads to altitude sickness is an exaggerated vascular response to hypoxia.
• Acclimatisation allows the body time to undertake various physiological adjustments at both the molecular and cellular level

Severity depends on four factors

• Rate of ascent
• Height above sea level
• Length of stay at that altitude
• Amount of physical exertion undertaken while there

Risk factors

• Rapid ascent, lack of acclimatization, and high altitude above 8,000 feet.
• Dehydration, Hypothermia
• High alcohol intake
• Excessive physical exertion in the first few days at altitude
• Previous anaemia
• Previous altitude sickness
• Previous pulmonary or cardiac pathology

Pathology

• Pulmonary oedema
• Protein rich exudate and alveolar haemorrhages
• Alveolar hyaline haemorrhage
• Cerebral oedema

Types

• High Altitude Pulmonary Oedema (HAPE): Fluid accumulation in the lungs, leading to extreme shortness of breath, coughing (sometimes with pink, frothy sputum), and cyanosis (bluish tint to the skin).
• High Altitude Cerebral Oedema (HACE): Swelling of the brain, which can cause confusion, loss of coordination, difficulty walking, and potentially coma.

Clinical

• Acute Mountain sickness: can be mild to severe
  • Headaches, Nausea, vomiting, Loss of appetite
  • Insomnia, sleeplessness, Dizziness, light headaches, confusion
  • Weakness, fatigue, heavy legs
  • Slight swelling of the hands and face
  • Breathlessness and irregular breathing
  • Reduced urine output
• High altitude pulmonary oedema
  • Breathless, Cough, Haemoptysis and wheeze
  • Tachycardia, Hypotension
  • Central cyanosis, Bibasal crackles
• High altitude Cerebral oedema
  • Confusion, Severe Headache, Ataxia
  • Irritability, Delirium, Coma, Seizures
• High ­Altitude retinal haemorrhage
  • Altered vision

Investigations

• FBC: Elevated Haematocrit and Hb
• ABG: low O₂ and low PCO₂
• ECG: sinus tachycardia
• CXR: pulmonary oedema

Management

• Avoidance
  • It is currently advised that the first night sleeping at altitude should be no higher than around 2400 m. Once above 2700 m, subsequent daily ascent should not exceed around 300 m. Other climbers feel it is allowable to ascend higher than your daily allowance of 300 m in one day, as long as you descend and sleep at a lower, ‘allowed’ altitude over night
  • Hike slowly – “pole-pole" (the Kilimanjaro shuffle)
  • No alcohol, sleeping pills or smoking
  • Drink enough liquids (3-4 litres a day) to prevent dehydration
  • Do not carry heavy daypacks (preferably 10-12 kg)
  • Climb higher, sleep lower (routes are planned accordingly)
  • Drink Diamox (please consult your doctor)
  • Tell others if you feel unwell
  • Start descending immediately if your symptoms get worse
  • The primarily prophylactic treatment is the carbonic anhydrase inhibitor acetazolamide (Diamox), which acts by stimulating the kidneys to excrete bicarbonate, making the blood more acidic, which in turn stimulates respiration, leading to an increased partial pressure of arterial oxygen
• AMS: Descent to ground level is mandatory: Where descent is indicated, but immediate descent is not possible (perhaps due to weather conditions), low flow oxygen therapy combined with a portable hyperbaric chamber or additional drug therapy can prove beneficial
• HAPE: Rapid Descent and Oxygen or Hyperbaric oxygen. Nifedipine and Sildenafil have been used
• HACE: High flow oxygen, Descent, Dexamethasone 8 mg QDS for cerebral oedema with Acetazolamide
• Hyperbaric Chambers: Portable hyperbaric chambers can simulate descent by increasing atmospheric pressure, which helps alleviate symptoms while preparing for actual descent.

References

• Altitude sickness / Acute Mountain sickness