Page 66 - Journal of Special Operations Medicine - Winter 2014

capacity in the HAPE-susceptible subjects of this study to 51 completed three tests previously used as part of
may have included the following: (1) enhanced nitric ox- the Automated Performance Test System to investigate
ide availability, contributing to lowered pulmonary artery the cognitive effects of exposure to high altitude. Dur-
pressure; (2) stimulation of alveolar sodium and water ing a 4-day period, participants were acclimatized to an
clearance, potentially improving oxygen diffusion; (3) ac- altitude of 12,139 feet. During the fifth day, participants
tivation of the sympathetic nervous system by acute hy- ascended to 15,748 feet and predexamethasone testing
poxia, leading to an increase in blood pressure, heart rate, was administered. None of the participants reported
and pulmonary vascular resistance; and (4) lowered levels symptoms of frank altitude illness at 15,748 feet. To re-
of an anti-inflammatory C-reactive protein. If used ap- duce acclimatization, participants descended to 12,139
propriately, at the very minimum, dexamethasone could feet within 4 hours. The first dose (4mg) of dexametha-
have an inhibitory effect on the sympathetic nervous sys- sone was given in the evening of day 5 and the second
tem, resulting in a decrease in heart rate, pulmonary vas- 4mg dose was given the following morning. Participants
cular resistance, and ventilatory rates. 25 then ascended back to 15,748 feet, where post-testing
was completed. The result was reduced susceptibility to
Ellsworth and colleagues examined the effects of acet- altitude illness and improved cognition in those partici-
23
azolamide or dexamethasone use versus placebo to pre- pants who were pretreated with dexamethasone.
vent AMS in 18 climbers ascending to an elevation of
14,409 feet. The climbers’ ascents were scheduled 2 weeks In addition to the cognitive and pulmonary benefits of
apart using a random numbers table. In this double-blind dexamethasone, physical performance may be improved
crossover study, dosage regimens consisted of either dexa- as well. Following a double-blind placebo- controlled ran-
methasone 4mg, acetazolamide 250mg, or lactose placebo domized crossover designed study, Casuso et al. found
27
every 8 hours starting 24 hours before the start of each that subjects (n = 17) at low altitudes who ingested 2 ×
climb and continuing until descent from the highest point. 2mg dexamethasone versus placebo for 5 consecutive
Dexamethasone was effective in reducing the incidence days saw increased high-intensity one-legged kicking
of AMS during rapid ascent for all subjects. Also, for the time to exhaustion 29 ± 35% longer and 20m shuttle run
dexamethasone only group, the overall rate of AMS was 19 ± 23% farther performances compared with a pla-
significantly lowered and the severity of AMS symptoms cebo. These high-intensity performance improvements
was decreased by an estimated 63%. Possible contribu- would be paramount to the short-term and long-term
tory mechanisms to this phenomenon may include im- survivability of SO forces in the field in addition to the
provements in microcirculatory integrity, reductions in other physiological benefits offered by dexamethasone.
cerebral blood flow, or cerebral vasoconstriction. 23

Maggiorini et al. determined whether tadalafil or Conclusions and Recommendations
20
dexa methasone reduced the severity of HAPE or HACE Dexamethasone is effective in the prevention and treat-
in a double-blind trial on 29 adult mountaineers with a ment of AMS, HAPE, and HACE and can be lifesaving
history of HAPE. The researchers reported that dexa- by effectively reversing physical symptoms that occur
methasone has the ability to stimulate sodium and water at high altitudes. This may allow SOs to sustain physi-
reabsorption while also increasing the release of nitric cal and cognitive performance while at altitude. The
oxide. These physiological responses were attributed to literature points to several different etiological mecha-
overall pulmonary vasodilation. Study subjects were nisms related to improvements in performance while at
20
randomly assigned to receive prophylactic dexametha- altitude. Maggiorini notes that dexamethasone reduces
sone 8mg, tadalafil 10mg, or placebo during a 24-hour systolic pulmonary artery pressure, while others have
ascent and 2-day stay at 14,900 feet. Both tadalafil and suggested an increase in maximal cardiac output and
dexamethasone were given 24 hours prior to the sub- improved pulmonary diffusion. 20,25,26 Additionally, these
jects’ rapid ascent. This was done to mitigate the risk mechanisms may contribute to increased oxygen trans-
of developing AMS as well as to reduce its overall in- port to working skeletal muscle tissues. 26
cidence. In particular, at 14,900 feet, there were lower
levels of systolic pulmonary pressure increases in sub- For those choosing to use dexamethasone, caution is
jects receiving dexamethasone. Hence, the researchers warranted. Healthy subjects who naturally perform well
reported that dexamethasone could be a viable prophy- at altitude should not take dexamethasone as an “er-
lactic choice prior to and during ascent to high altitudes. gogenic aid” to go higher and/or faster. Also, overcon-
fidence in the drug’s overall performance can lead to a
LaFleur and colleagues studied the effects of dexameth- poor risk assessment when preplanning for high-altitude
22
asone on improving the ability of participants to perform exposure. Furthermore, the use of dexamethasone as
28
various computerized psychomotor and cognitive tests. a prophylactic agent should be considered as an option
Six healthy adults (four men and two women) aged 26 per the US Special Operations Command guidance for

56 Journal of Special Operations Medicine Volume 14, Edition 4/Winter 2014