Hypothermia

HIGH ALTITUDE: 8,000–12,000 FEET (2,438–3,658 METERS)

• Commercial aircraft cabin pressure is typically equivalent to the pressure at about 8,000 feet (2,438 meters). • Altitude sickness is common above 8,000 feet (2,438 meters). • The availability of oxygen is only 65 percent to 90 percent of the amount at sea level. • Arterial PaO2 is significantly diminished. • Exercise performance decreases, and ventilation (the exchange of air between the lungs and the atmosphere) increases due to lower arterial PaCO2.

125 SEA LEVEL

• Atmospheric pressure is 765 mmHg (millimeters of mercury, the unit of measure for pressure in gases and liquids). • The partial pressure of atmospheric oxygen is 160 mmHg. • Arterial oxygen pressure (PaO2) is 80 mmHg to 100 mmHg. • Arterial carbon dioxide pressure (PaCO2) is 38 mmHg to 42 mmHg.

VERY HIGH ALTITUDE: 12,000–18,000 FEET (3,658–5,486 METERS)

• Atmospheric pressure is 483 mmHg or less. • The availability of oxygen is only 50 percent to 65 percent of the amount at sea level. • Arterial PaO2 falls below 60 mmHg. • Extreme hypoxemia (an abnormally low concentration of oxygen in the blood) may occur during exercise and sleep. • Severe altitude sickness occurs most commonly in this range.

EXTREME ALTITUDE: ABOVE 18,000 FEET (5,486 METERS)

• The availability of atmospheric oxygen drops below 50 percent of the amount at sea level. • Marked hypoxemia, very low PaCO2 and alkalosis (excessive alkalinity of the body fluids) are likely to occur. • All physiological functions progressively deteriorate. • No permanent human habitation exists above 20,000 feet (6,096 meters).

ALTITUDE SICKNESS / ACUTE MOUNTAIN SICKNESS

Traveling to high altitudes exposes people to increasingly rarefied air and progressively decreasing amounts of oxygen, resulting in declining levels of oxygen in the blood and thus impaired physical and mental performance. The response to high altitudes varies from individual to individual, but most people can operate normally at heights up to 8,000 feet (2,438 meters) above sea level. At altitudes greater than 8,000 feet, the oxygen deficit can begin to cause acute mountain sickness (AMS). At elevations higher than 10,000 feet (3,048 meters), 75 percent of people will experience at least mild AMS symptoms.

Symptoms: The onset of AMS symptoms varies according to the altitude, rate of ascent and individual susceptibility to the condition. A slow ascent will more likely allow your body to acclimate by establishing a more rapid spontaneous breathing rate to make up for the decreased oxygen in the atmosphere. Symptoms usually start 12 to 24 hours after your arrival at altitude and begin to decrease in severity by about your third day at a given elevation.

Mild AMS causes travelers to feel generally unwell. They may suffer headache, lightheadedness, fatigue, breathlessness, rapid heartbeat, nausea, difficulty sleeping or a loss of appetite. Symptoms tend to be worse at night. Mild AMS does not interfere with normal activities, and symptoms generally subside within two to four days as the body acclimates.

Severe AMS manifests itself in the form of serious conditions known as highaltitude pulmonary edema (HAPE) or high-altitude cerebral edema (HACE), which is the accumulation of excess fluid in the lungs (pulmonary) or brain (cerebral). The symptoms of severe AMS include a gray or pale complexion, a blue tinge to the skin (cyanosis), chest tightness or congestion, coughing

126

127

or coughing up blood, difficulty walking, shortness of breath when at rest, withdrawal from social interaction, confusion or decreased consciousness. Severe AMS can be fatal if not treated or if the victim is not returned to a lower altitude.

Treatment: Responding promptly to signs or symptoms of AMS is essential. Immediately call emergency medical services (EMS) if you or someone else experiences any of the following symptoms: • severe breathing problems • altered level of alertness • coughing up blood

If you cannot get EMS assistance, take the affected individual to a lower altitude as quickly and as safely as possible, and administer oxygen if it is available. Keep victims warm, and be sure they stay well hydrated if they’re conscious.

Prevention: To avoid altitude sickness, it is important to ascend slowly enough to allow time for your body to acclimate. Some people also find it beneficial to take prophylactic medication to help with the acclimatization process or to prevent some ill effects. If you plan to travel to a high-altitude location, ask your doctor or a travel clinic to evaluate your risk of altitude sickness, and obtain prophylactic medication that may prevent or alleviate AMS. If you plan to dive at a high-altitude site, make sure the medication is safe to use when diving.

AMS can affect anyone. Individuals are at higher risk if they • live at or near sea level and travel to a high altitude • have had AMS before • have preexisting medical conditions • ascend quickly to a high elevation

Do not travel to a high-altitude location without consulting your doctor if you have a heart, lung or blood disorder. You may need to travel with supplemental oxygen.

128

The following strategies can help prevent and/or moderate AMS: • Do not ascend quickly above 8,000 feet. • If you travel to high altitudes, choose a slow transportation method or walk. • If you get there by flying, do not overexert yourself or travel higher for the first 24 hours. • If you travel above 10,000 feet (3,048 meters), increase your altitude by no more than 1,000 feet (305 meters) per day. • After every 3,000 feet (914 meters) of elevation gained, take a rest day. • After daily excursions, return to a lower altitude for the night, if possible. • Don’t go higher if you experience any AMS symptoms; wait for the symptoms to subside. • If your symptoms increase, go to a lower elevation. • Stay properly hydrated. Drink at least three to four quarts of fluids per day, and be sure you are urinating regularly. • Performing light activity during the day is better than sleeping, because respiration decreases during sleep, which can exacerbate AMS symptoms. • Avoid tobacco, alcohol and depressant drugs (such as barbiturates, tranquilizers and sleeping pills), all of which worsen AMS symptoms. • Eat a high-carbohydrate diet while at altitude, but do not overeat.

DEHYDRATION

Dehydration occurs when the body’s level of water and other fluids falls below normal. Humans lose water through sweating, breathing and waste elimination. Medical problems that cause vomiting, diarrhea, edema or bleeding markedly increase this loss.

Symptoms: Even mild dehydration can result in poor judgment, weakness, headache and lack of energy; it can also make people more susceptible to infections, hyperthermia or decompression illness. Marked dehydration can cause imbalances in electrolytes (salts and other minerals in blood and other body fluids).

Individuals suffering from dehydration may also have a loss of elasticity in their skin, excessively dry mucous membranes (in the nose and throat, for example) and urine output that darkens in color and declines in quantity. If you have been swimming or diving, however, your first urine output after immersion may be clear even if you are dehydrated, which is due to immersion diuresis—that is, an increased production of urine during immersion due to vasoconstriction (narrowing of the blood vessels), which results in your urine being more diluted than it would be otherwise.

Dehydration is often suspected when someone feels unwell after having been physically active and sweating profusely in a hot, humid environment. The condition is much more difficult to detect in cooler environments, where an individual’s fluid intake still may not keep up with the loss of body fluids. Dehydration in such conditions can be gradual; victims may not be aware of their depleted state until an emergency arises, which can be especially dangerous if they are traveling in a remote area.

Treatment: Treatment of dehydration involves replacing the lost fluids and electrolytes—orally in cases of mild to moderate dehydration but intravenously in more severe cases. Administering frequent, small amounts of water is the best approach.

Prevention: Travelers in hot and humid environments may need to increase their fluid intake beyond the recommended 8 cups (almost 2 liters) of water per day. Don’t restrict your salt intake when traveling in such climates, because the loss of salts during prolonged exposure to heat and humidity may result in hyponatremia, which is characterized by abnormally low levels of sodium in the blood and can cause lethargy, headaches, seizures and even death if the brain swells due to ingestion of water but not enough salts and other electrolytes. This does not mean you should drink salt water, which can cause more dehydration. Studies of shipwreck survivors demonstrate that those who survived were those who refrained from drinking salt water.

129

130

OTHER EXPOSURE CONCERNS

While this guide cannot detail all possible sources of exposure-related injuries, the following are a few other serious or common problems.

Lightning: The Earth receives an estimated 100 lightning strikes per second, so it is not surprising that lightning sometimes strikes humans. The U.S. National Weather Service reports there were 20 fatalities from lightning strikes in the U.S. in 2019 and 17 fatalities in 2020.49 Worldwide estimates of lightning fatalities range from 6,000 to 24,000 cases per year.50 An individual’s lifetime odds of being killed by lightning are 1 in about 15,300.51

The CDC recommends the following strategies to avoid being struck by lightning: • Check the weather forecast before leaving for an outdoor excursion. • If you hear thunder, seek shelter in an enclosed building or a hard-topped vehicle with the windows rolled up. Avoid open structures or vehicles such as porches or golf carts. • Avoid ridgelines, mountain summits and isolated trees or other tall items such as power poles. If you are in the woods, stay near shorter trees. • Stay away from water such as swimming pools, ponds, rivers and even puddles. • Avoid tall structures. • Avoid contact with anything metal. If you are in a concrete structure, avoid leaning against the walls, because lightning can travel through the metal reinforcement in concrete.

131

• Do not wear or carry anything metal. • If you are in a group, separate from each other.

If lightning strikes you or someone with you, immediately call for emergency medical assistance and then take the following steps: • Minimize the risk of further strikes, and move the victim to a safer location if necessary. • Check to see if the victim is breathing and has a heartbeat. If not, immediately start chest compressions. Initiate rescue breathing if anyone in your group has CPR training. For more information about performing chest compressions and administering CPR, see Administering CPR in

Section 6. • Continue chest compressions and CPR until medical personnel arrive. • Assess the victim for other injuries such as burns or blunt trauma, and administer first aid as possible and appropriate. • If there is risk of hypothermia, place an insulating layer between the victim and the ground.