Page 636 - Clinical Application of Mechanical Ventilation

602 Chapter 18

High-Altitude Cerebral and Pulmonary Edema
At 8,000 ft above sea
level, the barometric pressure
(P B ) is 564 mm Hg, and the At 8,000 ft above sea level, the barometric pressure (P ) is 564 mm Hg, and the cal-
B
calculated P A O 2 at this altitude
is only 59 mm Hg. culated P O at this altitude is only 59 mm Hg (Chang, 2011). An acute drop in the
2
A
P and P O are the primary reasons for high-altitude illness experienced by unaccli-
2
A
B
matized persons. Acute mountain sickness includes a number of nonspecific subjective
symptoms. They may include presence of headache and at least one of the following
Acute mountain sickness symptoms: gastrointestinal disturbances (anorexia, nausea, or vomiting), insomnia,
may include presence of dizziness, and fatigue. In severe high-altitude illness, cerebral edema or pulmonary
headache and at least one
of the following symptoms: edema could develop and these conditions are potentially fatal (Hackett et al., 2001).
gastrointestinal disturbances High-altitude cerebral edema is related to vasodilatation of cerebral vessels, overper-
(anorexia, nausea, or vomit-
ing), insomnia, dizziness, and fusion, and inadequate volume buffering by cerebrospinal fluid. The treatment for
fatigue. acute mountain sickness or high-altitude cerebral edema includes one or a combina-
tion of the following: descent to a lower altitude, and use of supplemental oxygen.
When descent is not possible or supplemental oxygen is not available, acetazolamide
(Diamox) and dexamethasone may be useful to treat the symptoms associated with
The treatment for acute mountain sickness. In the event that high-altitude cerebral edema does not
acute mountain sickness or
high-altitude cerebral edema respond to the initial treatments, further descent or use of a portable hyperbaric
includes one or a combination chamber may be necessary (Hackett et al., 2001).
of the following: descent to
a lower altitude, and use of High-altitude pulmonary edema is primarily noncardiogenic in origin, but it is as-
supplemental oxygen. sociated with pulmonary hypertension and elevated capillary pressure. The signs
and symptoms of this type of pulmonary edema may include decreased endurance,
dry cough, pink or bloody sputum, resting tachycardia, and tachypnea. Chest radi-
ography and breath sounds resemble typical pulmonary edema (Hultgren, 1996).
High-altitude pulmonary High-altitude pulmonary edema accounts for most fatalities from high-altitude ill-
edema is noncardiogenic,
but it is associated with ness. As is the case for acute mountain sickness, the incidence of high-altitude pulmo-
pulmonary hypertension and nary edema is related to the rate of ascent to the high altitude, the altitude reached,
elevated capillary pressure.
individual susceptibility, and exertion. Cold can be a contributing factor as it causes
sympathetic stimulation and a resulting increase in pulmonary artery pressure (Reeves
et al., 1993). The treatments for high-altitude pulmonary edema include descent
to lower altitude, supplemental oxygen, and use of a portable hyperbaric chamber.
The treatments for Nifedipine, a calcium channel blocker, may be used when descent or medical equip-
high-altitude pulmonary
edema include descent to ment and supplies are not available. Nifedipine relieves acute pulmonary edema due
lower altitude, supplemental to its antihypertensive property, which effectively reduces the pulmonary artery pres-
oxygen, and a portable
hyperbaric chamber. sure (Oelz et al., 1989).

Airplane Cabin Pressure

Most commercial airplanes travel at a cruising altitude between 25,000 ft and
For the safety and com- 40,000 ft. At high altitudes, the air becomes thinner (less dense) and this condition
fort of the passengers inside
the commercial airplanes, lowers the airflow resistance to the airplane. Since less thrust is needed to move at a
most airplanes are pressurized given speed, the airplanes can fly more efficiently at higher altitudes. A lower cabin
to a cabin pressure altitude of
8,000 ft (range from 5,000 ft pressure also makes the airplane lighter and consumes less fuel. For the safety and
to 8,000 ft). comfort of the passengers inside the airplane, most airplanes are pressurized to a
cabin pressure altitude of 8,000 ft (range from 5,000 ft to 8,000 ft).

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