Acute Mountain Sickness

Acute mountain sickness is when your body is not able to adjust to the atmosphere and lower oxygen pressure at high altitudes. It is preventable and treatable nowadays but when severe, it can rapidly turn into a life-threatening condition. The trekkers should be able to recognize the symptoms early to pause their ascent which can further lead to worse symptoms.

Pathophysiology of Acute Mountain Sickness 

• It is also called high-altitude pulmonary edema.
• Due to low oxygen at high altitude, the patient will experience hypoxia that will lead to patchy pulmonary vasoconstriction. 
• This leads to an increase in hydrostatic pressure in proximal areas.
• The over-perfusion of proximal areas of the lungs will occur and it increases shear that will cause the capillary stress failure.
• This leads to extravasation of fluid into alveoli and it causes noncardiogenic pulmonary edema. 
•  The second reason for an increase in hydrostatic pressure is pulmonary vasoconstriction due to sympathomimetic stimulation due to extremely harsh weather and exercise.
• In noncardiogenic pulmonary edema, the left atrium on the echocardiogram shows normal function and pressure.
• Another mechanism is proposed to define acute mountain sickness. The endothelial cells are responsible for nitric oxide production and this nitric oxide causes vasodilation.
• If the endothelial cells are damaged by hypoxia this leads to a decrease in the quantity of nitric oxide.
• Again the constriction in pulmonary capillaries will occur causing the extravasation of the fluid from pulmonary capillaries into alveoli.
• Phosphodiesterase 5 inhibitors are used for treatment.

Also Read: Bronchiectasis : Causes, Pathophysiology

Clinical features of Acute Mountain Sickness

• It is mostly seen in young people as this age group treks routinely.
• It usually occurs on arrival at 2000 to 2500 meters of height. It usually occurs on days 2 to 4

Symptoms of Acute Mountain Sickness

• Fatigue
• Shortness of breath
• Decreased exercise tolerance
• Nonproductive cough that can also cause a rib fracture.
• Cyanosis
• Bloating
• Flatulence
• Bilateral crackles 
• Increased respiratory rate and heart rate
• Altered mentation
• On arterial blood gas analysis, respiratory alkalosis will be observed.
• On Echocardiography, pulmonary artery hypertension with right ventricular strain will be found. 
• Left atrial pressure is normal in these patients.

Chronic Mountain Sickness

• It is common among residents of Tibet.
• People who are living at high altitudes have chronic long-standing hypoxia that leads to an increase in erythropoietin production from the kidneys. This causes increased erythrocytosis due to secondary polycythemia. This further causes sluggish circulation called Monge's Disease.
• The hypoxia causes pulmonary artery hypertension and right ventricular failure and consequently leads to core pulmonale.
• The treatment is Venesection, that is blood is removed from the body.
• Acetazolamide can also be a drug of choice. 

Prevention and Treatment of Acute Mountain Sickness

• The gradual ascent should be done 1000 feet.
• Acetazolamide is a carbonic anhydrase inhibitor.
  • It causes the loss of bicarbonate in urine. 
  • This loss of bicarbonate from the blood leads to metabolic acidosis as the protons are created.
  •  This leads to stimulation of the respiratory center and hence it causes hyperventilation. 
  • It should be taken at night before the trekking. 
  • If the patient is allergic to sulfa drugs then the alternative to acetazolamide is dexamethasone.
• For mild acute mountain sickness, ascent should be discontinued and immediate dissent should be done. 
• Acetazolamide should be continued.
• For moderate acute mountain sickness, immediate descent is recommended.
  • Low flow oxygen should be started and the combination of acetazolamide and dexamethasone should be used.
  • Gamow bag should be used for hyperbaric therapy. It is a portable altitude chamber operated by a foot pump and it causes simulated descent.
• If the patient develops high-altitude cerebral edema, immediate descent or evacuation should be done. The oxygen delivery should be 2 to 4 liters per minute and the drug of choice is dexamethasone which can be given intravenous or intramuscular.
• If the patient develops high-altitude pulmonary edema then immediate descent or evacuation should be done and oxygen flow should be maintained at 4 to 6 liters per minute. Calcium channel blocker, Nifedipine is the drug of choice that causes vasodilation and it is very useful in this condition.
• Some other drugs like salmeterol which is a beta 2 agonist can be used for its management. It causes the clearance of sodium and water from alveoli.
• Phosphodiesterase 5 inhibitor increases the nitric oxide levels, hence can be helpful.

Also Read: Primary Biliary Cholangitis : Pathophysiology, Clinical Features

Download the PrepLadder app now to access high-yield content with 24-hr Free Trial. Explore premium study resources like Video Lectures, digital notes, QBank, and Mock Tests for a seamless exam preparation. Start your NEET PG online coaching journey with PrepLadder.