Wilderness and Rescue Medicine 7th Edition Jeffrey Isaac, PA-C and David E. Johnson, MD

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Section V: Environmental Medicine

during sleep when breathing normally slows. It also inhibits the adjustment process.

Alpinists can continue to ascend if they allow enough time for short and long-term adjustment. How quickly this occurs and how high a person can ultimately go depend on health, fitness, and genetics. Eventually, the ability to compensate is maximized and inadequate cellular oxygenation prevents further ascent. Cerebral and Pulmonary Edema Reduced oxygen in the blood and body tissues results in edema due to capillary dilation and leak- age. This generally occurs as oxygen saturation falls below about 90%. The mechanism is not com- pletely understood and is different in the brain than in the lungs. But, the signs and symptoms we worry about most are the same as those seen in cerebral or pulmonary edema from other causes. High-altitude cerebral edema (HACE) is caused by vascular changes that result in capillary leakage of fluid into the brain. High-altitude pulmonary edema (HAPE) is the result of vascular changes in the lungs that have the effect of forcing fluid to leak from capillary beds in the lungs into the alveoli. HACE looks similar to elevated intracranial pressure (ICP) from a traumatic brain injury (TBI) or any other cause of brain tissue damage. The signs and symptoms of HAPE are similar to those of pulmonary edema from heart problems, infection, or drowning events. High-Altitude Cerebral Edema The symptoms of mildHACE are often called acute mountain sickness. A small amount of cerebral edema produces the characteristic headache, loss of appetite, and nausea associated with the slight increase in ICP. These are the same symptoms one might expect following a mild TBI. Acute mountain sickness generally develops within a few hours of arrival at moderate altitudes and resolves within 48 hours for most people.

General Principles

Compensation at Altitude Short Term: • Hyperventilation • Tachycardia and increased blood pressure • Kidneys trying to maintain normal pH Long Term: • Body produces more red blood cells and hemoglobin • Capillary beds increase in density

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As part of the short-term adjustment the kid- neys excrete bicarbonate (a base) to maintain the pH balance despite the increased respiratory rate. This usually takes 2 or 3 days and may or may not be completely successful. Patients can help the process by avoiding climbing higher until adjusted to the new altitude and by maintain- ing adequate hydration for kidney function. A medication called acetazolamide can help with this process.

General Principles

Side Effects of Compensation

Hyperventilation

Respiratory Alkalosis

Irregular Respiratory Control

Sleep Hypoxia and Delayed Adjustment

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Long-term compensation for an individual staying at altitude includes producing more red blood cells to carry oxygen and the development of more dense capillary beds in body tissues. This process can take months to years. The acclima- tized individual’s oxygen saturation will still read low, but because the carrying capacity of the blood has increased, there is actually more oxygen being transported.