tangent
07-02-02, 21:54
Anderson, W, Hypothermia in the Austere Environment, J Spec Operations Med, v2n2, Sprint 2002, p72-3
The last edition of the Journal of Special
Operations Medicine, Winter, contained an article
on hypothermia. The author, Gordon Giesbrecht,
PhD, provided a good overview of the current state
of the art in this troublesome problem. However,
the problems of field treatment by SOF medics
remain.
Recent combat experience in Afghanistan,
as reported in Army Times and elsewhere, has
involved unexpected exposure to the cold at high
altitude. A helicopter insertion expected to last
only a few hours stretched into a night-long ordeal
when the LZ came under intense, determined
enemy fire. For troops going into combat, every
pound of "snivel gear" they carry is a pound of
ammo they must leave behind.
Hypothermia is arbitrarily divided into
mild, moderate, and severe. This division is based
upon core body temperature and serves a specific
purpose - guiding therapy in the emergency depart-
ment. However, in the field and under the care of
the SOF medic, another way to classify hypother-
mia is shivering hypothermia and non-shivering
hypothermia.
In shivering hypothermia, the patient needs
insulation, fluids and fuel. The patient will almost
always be able to swallow fluids, and so hot fluids,
where tactically sound, make good sense.
However, heating the fluid is definitely a secondary
consideration.
Why?
For ease of calculation, your patient is a
100-kilogram soldier, or 220 pounds. His body
temperature, if you had a thermometer, would
measure 94 degrees. You heat a liter of fluid to 114
degrees, 20 degrees above his temperature. When
he drinks the fluid, assuming it remains at 114
degrees the entire time he drinks it, he will in effect
be making 1% of his body weight 20 degrees high-
er - and making his whole body weight 0.2 degrees
higher. If you want to raise his core temperature to
98 degrees, then you are only 5% of the way there.
Of course, that's better than cooling him further
with ambient (cold) fluids, but the point is that
health care personnel often overestimate the effica-
cy of their interventions.
Another recommended intervention, heat-
ed intravenous fluids, is frequently used in the
emergency department. Here, the vein will not tol
erate a 114-degree fluid, so this intervention seems
almost silly. Indeed, in the best-case scenario, the
nurse places the liter of fluid in the microwave for
a couple minutes prior to giving the fluid. Then,
almost invariably, no one wraps the IV tubing on its
course to the IV site. The fluid, regardless of how
hot it is leaving the bag, will enter the vein at ambi-
ent temperature, effectively cooling the patient. If
the tubing is wrapped with fluffy gauze and the
tubing routed along the arm, then the best one can
hope for is that the fluid will enter the vein at the
patient's (hypothermic) temperature.
In the field, I have successfully heated IV
fluid by dropping a loop of the tubing into a can-
teen cup of hot water just before it enters the vein.
Others have successfully used MRE chemical
heaters for the same purpose, but there is always
danger of thermal burns and explosion of the heat-
ed air, depending upon the method used.
Another frequently recommended tech-
nique of re-warming, inhalation of heated mist,
requires a fairly elaborate setup and probably is
hard to do in an austere environment, aside from
putting another canteen cup of very hot water under
a facial tent fashioned from a MylarŪ casualty
blanket.
In the emergency department, it is common
for the respiratory therapist to place the heater at
the portion of the inhalation circuit distal to the
patient, and unless a veritable blanket of gauze is
wrapped in the tubing, the temperature will again
be ambient.
A study of chilled SEALS, conducted at the
US Navy Experimental Diving Unit in Panama
City, Florida showed that warmed inhalation pre
vents heat loss through expired air, but does almost
nothing to actually re-warm the patient.
In the end, the shivering patient needs
insulation, fluid, and fuel so he can make his own
heat. Providing a euthermic person a sleeping bag
will be helpful, and placing warm canteens on the
patient's axillae, inguinal regions, and neck will help
speed the process. Also, a warm canteen on the scalp
will provide a great deal of comfort and enhance the
re-warming. A surgical mask, oxygen mask or cravat
('bandit") mask will help prevent inhalation of cold
ambient air.
A non-shivering patient in an austere envi-
ronment will not make his own heat, and will contin-
ue to lose heat unless actively re-warmed. Gentle
handling and getting a couple other soldiers under
the insulation with the patient will help as much as
anything. Again, warm canteens in the appropriate
places and a mask will help. Rescue breathing,
given enough people, can continue almost indefi-
nitely in the absence of spontaneous respirations,
and will even supply warmed air to the patient. In
the absence of a pulse, in an austere environment,
there is little utility in chest compressions and the
medic should take some comfort from the realiza-
tion that compressions may convert a very weak
bradycardia into a ventricular arrhythmia, and thus
could do more damage than help. Under the best
hospital conditions, re-warming a moderately-
severe hypothermic patient takes several hours. The
prognosis is guarded, at best.
The last edition of the Journal of Special
Operations Medicine, Winter, contained an article
on hypothermia. The author, Gordon Giesbrecht,
PhD, provided a good overview of the current state
of the art in this troublesome problem. However,
the problems of field treatment by SOF medics
remain.
Recent combat experience in Afghanistan,
as reported in Army Times and elsewhere, has
involved unexpected exposure to the cold at high
altitude. A helicopter insertion expected to last
only a few hours stretched into a night-long ordeal
when the LZ came under intense, determined
enemy fire. For troops going into combat, every
pound of "snivel gear" they carry is a pound of
ammo they must leave behind.
Hypothermia is arbitrarily divided into
mild, moderate, and severe. This division is based
upon core body temperature and serves a specific
purpose - guiding therapy in the emergency depart-
ment. However, in the field and under the care of
the SOF medic, another way to classify hypother-
mia is shivering hypothermia and non-shivering
hypothermia.
In shivering hypothermia, the patient needs
insulation, fluids and fuel. The patient will almost
always be able to swallow fluids, and so hot fluids,
where tactically sound, make good sense.
However, heating the fluid is definitely a secondary
consideration.
Why?
For ease of calculation, your patient is a
100-kilogram soldier, or 220 pounds. His body
temperature, if you had a thermometer, would
measure 94 degrees. You heat a liter of fluid to 114
degrees, 20 degrees above his temperature. When
he drinks the fluid, assuming it remains at 114
degrees the entire time he drinks it, he will in effect
be making 1% of his body weight 20 degrees high-
er - and making his whole body weight 0.2 degrees
higher. If you want to raise his core temperature to
98 degrees, then you are only 5% of the way there.
Of course, that's better than cooling him further
with ambient (cold) fluids, but the point is that
health care personnel often overestimate the effica-
cy of their interventions.
Another recommended intervention, heat-
ed intravenous fluids, is frequently used in the
emergency department. Here, the vein will not tol
erate a 114-degree fluid, so this intervention seems
almost silly. Indeed, in the best-case scenario, the
nurse places the liter of fluid in the microwave for
a couple minutes prior to giving the fluid. Then,
almost invariably, no one wraps the IV tubing on its
course to the IV site. The fluid, regardless of how
hot it is leaving the bag, will enter the vein at ambi-
ent temperature, effectively cooling the patient. If
the tubing is wrapped with fluffy gauze and the
tubing routed along the arm, then the best one can
hope for is that the fluid will enter the vein at the
patient's (hypothermic) temperature.
In the field, I have successfully heated IV
fluid by dropping a loop of the tubing into a can-
teen cup of hot water just before it enters the vein.
Others have successfully used MRE chemical
heaters for the same purpose, but there is always
danger of thermal burns and explosion of the heat-
ed air, depending upon the method used.
Another frequently recommended tech-
nique of re-warming, inhalation of heated mist,
requires a fairly elaborate setup and probably is
hard to do in an austere environment, aside from
putting another canteen cup of very hot water under
a facial tent fashioned from a MylarŪ casualty
blanket.
In the emergency department, it is common
for the respiratory therapist to place the heater at
the portion of the inhalation circuit distal to the
patient, and unless a veritable blanket of gauze is
wrapped in the tubing, the temperature will again
be ambient.
A study of chilled SEALS, conducted at the
US Navy Experimental Diving Unit in Panama
City, Florida showed that warmed inhalation pre
vents heat loss through expired air, but does almost
nothing to actually re-warm the patient.
In the end, the shivering patient needs
insulation, fluid, and fuel so he can make his own
heat. Providing a euthermic person a sleeping bag
will be helpful, and placing warm canteens on the
patient's axillae, inguinal regions, and neck will help
speed the process. Also, a warm canteen on the scalp
will provide a great deal of comfort and enhance the
re-warming. A surgical mask, oxygen mask or cravat
('bandit") mask will help prevent inhalation of cold
ambient air.
A non-shivering patient in an austere envi-
ronment will not make his own heat, and will contin-
ue to lose heat unless actively re-warmed. Gentle
handling and getting a couple other soldiers under
the insulation with the patient will help as much as
anything. Again, warm canteens in the appropriate
places and a mask will help. Rescue breathing,
given enough people, can continue almost indefi-
nitely in the absence of spontaneous respirations,
and will even supply warmed air to the patient. In
the absence of a pulse, in an austere environment,
there is little utility in chest compressions and the
medic should take some comfort from the realiza-
tion that compressions may convert a very weak
bradycardia into a ventricular arrhythmia, and thus
could do more damage than help. Under the best
hospital conditions, re-warming a moderately-
severe hypothermic patient takes several hours. The
prognosis is guarded, at best.