Altitude is measured by feet (or meters) above sea level. The important thing to remember is that the partial pressure of oxygen decreases with the increase in altitude. In other words, the higher up you are, the less oxygen is available for breathing. This could be a bummer. The signs and symptoms associated with altitude sickness are directly and indirectly related to hypoxia. Because we are all different, we all respond differently to altitude and therefore each patient can present with unique sequelae. Some people are just more susceptible to altitude illness.
HVR: Hypoxic Ventilatory Response
HVR is the result of a decrease in blood oxygen saturation and ventilation after a few hours at altitude. Altered fluid homeostasis also occurs – which means that fluid is redistributed from the intravascular to the intracellular and extracellular spaces – and the result can be peripheral and/or pulmonary, and/or cerebral edema.
HACE: High Altitude Cerebral Edema
HAPE: High Altitude Pulmonary Edema
HAFE: High Altitude Flatus Expulsion
AMS: Acute Mountain Sickness
AMS is a continuum of signs and symptoms that can range from loss of appetite and headache to coma and death. AMS is generally described as mild, moderate or severe.
Mild AMS: Patients may experience headache relieved by rest and medication, nausea, loss of appetite and insomnia. Nothing is visible on physical exam. Advise the patient to stop the ascent until the symptoms disappear. The goal is to hydrate, hydrate, hydrate and eat – in spite of the anorexia
Moderate AMS: These patients may complain of headache not relieved by rest or medication, nausea and vomiting, shortness of breath, fatigue and weakness at rest, loss of appetite, and insomnia. Most of the symptoms are caused by hypoxia, so supplemental oxygen is a must. Patients should descend 1000 – 2000 feet. Ski patrol teams and ambulances operating in the mountains encounter these patients with relative frequency.
Hydration is also a key to treatment. If vomiting continues, prochlorperazine (Compazine®) can be administered as an antiemetic. Acetazolamide (Diamox®) may also be helpful. Watch these patients for worsening of symptoms.
Severe AMS: These patients exhibit all of the signs and symptoms of moderate AMS and: sometimes ataxia, dyspnea at rest, tachycardia, and as HAPE (high altitude pulmonary edema) begins patients may begin with a persistent dry cough followed by rales upon auscultation. Late in severe AMS some patients experience blood tinged sputum. Hypoxia worsens with tachycardia. AMS occurs late in AMS (altered mental status occurs late in acute mountain sickness. HACE (high altitude cerebral edema) may also occur. Proper care is Oxygenation and descent, with administration of dexamethazone (Decadron®) for HACE, acetazolamide (Diamox®) and nifedipine (Adalat®) for HAPE.
Acetazolamide (Diamox®) – What is it and what does it do?
It is a diuretic that indirectly causes enhanced ventilatory acclimation and decreases cerebral spinal fluid production. It is indicated for patients with moderate or severe AMS and for rescuers making rapid ascents to reach these patients. Since it is a diuretic, it causes polyuria and possibly dehydration if adequate fluid intake is not maintained.
Dexamethazone (Decadron®) – What is it and what does it do?
It is a steroid with anti-inflammatory effects. While it is effective at treating AMS and HACE, the symptoms can rebound once the medication is stopped.
So, now we have HAPE, HACE and just what is HAFE? High altitude flatus expulsion. Supposedly, intralumenal bowel gas expands with decreased barometric pressure causing flatus. If necessary, simethicone (Phazyme®, Gas-X®) can be used to treat it.
Understanding how to treat patients with AMS is important, but understanding how to protect the rescuer and how not to become a patient is also a priority. Be a rescuer…don’t become a victim.
Burke, TG. Altitude illness. Prehospital Emergency Medicine Secrets. Hanley and Belfus, Philadelphia, 1998.
Fogerty, WW. (ed): Wilderness Medical Society Practice Guidelines for Wilderness and Environmental Emergencies. Merrillville, IN. ICS Books, 1995.
Hackett, PH, Roach, RC: High altitude medicine. In Auerbach, PS (ed): Wilderness Medicine: Management of Wilderness and Environmental Emergencies, 3rd ed. St. Louis, Mosby, 1995, pp 1-37.
Hackett PH, Rennioe D: The incidence, importance and prophylaxis of acute mountain sickness. Lancet 2(7996):1149-1155, 1976.
Johnson, TS, Rock, PB: Acute mountain sickness. N ENgl J Med 319:841-845, 1988.
Larson EB, Roach, RC, SChoene RB, Hornbein, TF: Acute mountain sickness and acetazolamide. JAMA 248:328-332, 1982.
Tilton B (ed): Wilderness Medicine Handbook, 2nd ed. Pitkin, CO, Wilderness Medical Institute, 1997.