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The Use of Hyperbaric Oxygen for Combat Casualties at Altitude
In 1976, the United States Army commissioned an assessment of every battle casualty death
in Vietnam. It was discovered that 50% died of shock, and immediate steps were
implemented in first aid training and field medical practice to reduce those deaths. Today,
those procedures and improved body armor have further reduced deaths in combat. The
high altitudes of Afghanistan have added lower atmospheric oxygen (which leads to hypoxic
shock) to the casualty survival equation. The solution is hyperbaric oxygen treatment
(HBOT), to saturate the casualty's tissues with oxygen to restore metabolism and reduce
secondary tissue damage.
Today science has learned that hyperbaric medicine is not just about "treating bubbles."
HBOT reverses and prevents tissue injury from acute trauma, such as bruising, swelling, and
scar tissue formation. It reduces healing time by preventing these secondary injuries,
increases healing speed by 50%, fights infection, and can reduce future long term disability.
HBOT can be used in three ways for combat casualties. First, HBOT can be used for the
treatment of combat wounds and to reverse the effects of hypoxia prior to transport. Every
wound is a hypoxic event; the wound is an area of the body deprived of its normal blood
supply. For a small laceration this area may be trivial at first, but becomes more significant
with the collection of blood, serum, and devitalized tissue in the wound. The concept of
immediate treatment of casualties in trauma is long standing and is expressed in concepts
such as the “golden hour” used to signify the time immediately after wounding in which
immediate effective treatment can be life or limb saving and is capable of preventing future
complications. This is the reason for the USSOCOM Combat Pill Pack to be taken
immediately after wounding. HBOT can be thought of as an adjunct to other drugs used
early after wounding.
The early provision of HBOT after wounding may be life or limb saving where there is
significant blood loss (accounting for the majority of combat deaths). If circulation can be
maintained with fluids, transfusion is unnecessary in the hyperbaric chamber, gaining
precious time until blood transfusion may be available. HBOT can support damaged tissue,
perhaps preventing amputation. Early in the War on Terror, the average evacuation time in
Afghanistan was 18 hours for the wounded. In this time period, HBOT would have been
invaluable. Weather, lack of suitable transportation, and the conditions of combat in future
engagements may result in delays in which HBOT could make a significant difference in
outcome.
The second use of HBOT for the combat wounded would be to provide support during
helicopter transport. The hypoxic wound and tissues hypoxic from blood loss would benefit
significantly from HBOT during transport. With the Emergency Evacuation Hyperbaric
Stretcher (EEHS or SOS Hyperlite) which has been approved for use in aircraft, HBOT can
be provided during transport on any airframe without regard for cabin altitude. The EEHS
can be pressurized to sea level and transport could be accomplished without the
accompanying hypoxia in an open or partially pressurized cabin, even in the C130, C17,
CV22, or helicopters. Simply pressurizing the EEHS with air would provide a 46% increase in
inspired oxygen at 10,000 ft. above sea level. Breathing 100% oxygen, the normal situation
in the EEHS, the patient at 10,000 ft. would experience a 7 fold increase in inspired oxygen if
the chamber were pressurized to sea level, and a 17 fold increase in inspired oxygen if the
chamber were pressurized to 2.4 atmospheres absolute (ATA), the usual wound care
pressurization. This type of hyper-oxygenation for the injured is precisely what makes HBOT
so valuable at altitude. Not only are the injured protected against the vicissitude of hypoxia
at altitude, they actually receive all the benefits of HBOT for wound healing, tissue
preservation, and life preservation.
Finally, the third use of HBOT for combat casualties at altitude is hyperbaric preconditioning.
Recently it has been learned that HBOT is capable of preconditioning tissue so that it is more
resistant to the effect of low oxygen tension or hypoxia and less likely to suffer injury from
an hypoxic insult, such as that which would be encountered during air evacuation from
altitude. The preconditioning effect of HBOT is especially protective for myocardium and
neural tissue such as the injured brain. The effect is achieved because HBOT signals cells to
up regulate cell repair and preserving processes which are protective in hypoxia. HBOT
could be provided on the ground to the injured prior to flight, for example while waiting for
evacuation, in a standard hyperbaric chamber or the EEHS. For evacuation, if the injured
were removed from the hyperbaric chamber, they would still experience the benefit of
HBOT preconditioning for hours, perhaps days. HBOT could be used for all cases of trauma
where tissue is hypoxic to improve outcomes. This is a very exciting recent discovery, which
is being discussed in trauma and surgery and awaits implementation on a large scale.
In just the last twenty years, major advances in molecular biology and the physiology of
wound healing have given us the tools to understand how HBOT heals. HBOT is causing
biological repair and regeneration in acute trauma and chronic care patients. It is FDAapproved. It has known safety precautions and rare side-effects. Twenty-five years ago
there were barely 30 civilian locations in the nation where HBOT treatment could be
obtained. Today there are over 1,000. With the addition of portable hyperbaric equipment,
like the SOS Hyperlite(r), HBOT is now available to treat war casualties at the Forward Edge
of Battle. It can assist the commander with recovery in theater. This will increase combat
readiness and effectiveness, and improve retention. Further, it will reduce long term
disability and improve outcomes in casualties who need more extensive care.
This article is reprinted by courtesy of the International Hyperbaric Medical Association. It
is Appendix A of their High Altitude Mortality Reduction (HAMR) Project for FY’09-FY'11.
Kenneth Stoller, M.D., President www.HyperbaricMedicalAssociation.org