ALTITUDE AND COMMON MEDICAL CONDITIONS - Medicine for Mountaineering and Other Wilderness Activities - page 363

angina, hypertension, or other problems. Despite these limitations, a physician attempting
toevaluatetheriskofaltitudeforapersonwithCOPDmaywanttousethepredictedinitial
resting arterial oxygen pressure at altitude as a way to determine the need for supplemental
oxygen ( Fig. 25-1 ) .
Efforts to predict oxygenation at high altitude in children with hypoxemic lung disease
have found that hypoxic challenge with air containing 15 percent oxygen is a better way to
identify individuals who might require supplemental oxygen during flight or in the moun-
tains than measuring breathing capacity and oxygen saturation. The main value of provoc-
ative testing is to determine the need foroxygen while at rest at altitude, but further assess-
ment of oxygen saturation during activity and sleep is needed to ensure a correct oxygen
prescription.
Oxygen therapy may be required for persons who are symptomatic at altitude or for
thosepredictedtobecomeseverelyhypoxemic.Forthosealreadyonsupplementaloxygen,
the amount of inspired oxygen should be increased by the ratio of higher to lower baro-
metric pressures. Whether acetazolamide and medroxyprogesterone acetate, both of which
aid acclimatization by stimulating ventilation, might be useful (or harmful) in individuals
withCOPD,especiallywithelevatedbloodcarbondioxideconcentrations,isunknown.In-
dividuals should have pulmonary function optimized prior to ascent to altitude and should
receive instructions on medication use (including oxygen) if problems develop.
In summary, information regarding the effect of altitude on chronic lung disease is ex-
tremely limited. Predicting who will tolerate and who may be harmed by the additional
hypoxia of altitude often is a difficult, possibly futile undertaking, leaving old-fashioned
clinical judgment based upon the overall health and capacity to function of each individual
as the best guidance available.
Asthma
Data on mortality and morbidity from asthma in high-altitude residents are scant. The
availableinformationsuggeststhatasthmamaybelessofaproblemathighaltitudethanat
sea level, both for residents and sojourners, because allergens and pollution are decreased.
Studies worldwide have reported improvement in childhood asthma at altitude, which has
been a popular treatment for asthma in Europe for many decades.
Surprisingly, in view of the possibility of greater hypoxemia during asthmatic bron-
choconstriction at altitude, no association between asthma and highaltitude pulmonary ed-
ema or AMS has been reported, nor has unexpected asthma exacerbation in lowlanders at
altitude been described. Likewise, no information documents the value of a variety of lo-
gical clinical aids for prevention, including increased hydration or the use of an airway
warming mask.
Whether a severe asthma attack at high altitude puts a person at greater risk than at low
altitude—an important question—is unanswered.