Hypothermia
and the Cave Rescue Environment: A review of treatment and
advanced pre-hospital provider care
Greg
L. Turner
In
cave rescues, presume hypothermia to be present. On the
East Coast of the U.S. most caves are 54†F year round; the
majority are wet, often with standing water. Heat loss is
increased in wet environments. Victims of cave-related accidents
are generally non-mobile and traumatized, and there is often
a time delay in reaching them. In a cave rescue, the environment
is generally cool, and air flow and improper care by Emergency
Medical Service (EMS) personnel, such as the use of non-heated
fluids and oxygen, can further complicate an otherwise stable
patient.
Methods
of Heat Loss and Preventative Measures
The
patient in a typical cave rescue setting is faced with fighting
all of the five methods through which heat is lost to the
environment: conduction, convection, radiation, evaporation,
and respiration.
Conduction
is often one of the first to affect the victims because
they have direct contact with cold surface such as the cave
floor. This problem can be addressed by insulating the patient
by placing a Thinsulate pad or similar pad underneath him
or her. Pads should be made of foam and not the air-filled
type, because air conducts the heat away from the patient.
Rescuers cover victims with insulated materials, but often
forget that the fastest way patients loose heat is through
body contact with the cave floor.
Convection
occurs when heat is lost through air movement over patientís
body such as a draft. Since caves and the passages therein
blow air constantly, anyone left in a main trunk passage
will be exposed to an increase in convective loss. This
loss can easily be address by placing the patient out of
the main passage when waiting. The small side passages,
alcoves, and holes found in most caves are excellent places
where a patient can be protected from further convective
heat loss.
Radiation
is the loss of heat to the environment as a result of electromagnetic
waves. This loss is best characterized by heat lost because
the patient is not covered. Heat waves, characterized by
a light fog, are normally seen rising from a normothermic
caver. Therefore, an injured or hypothermic caver must be
protected with extra covering to prevent further heat loss.
Evaporation
is the loss of heat by the drying of moisture on skin,
such as sweating. Since caving is a vigorous activity, skin
moisture is expected to build up in the form of perspiration
during normal activities. When the caver becomes immobile,
this moisture can be a source for heat to transfer to the
environment. This form of heat loss is lessened by wearing
layers of clothing and ensuring that the layers wick moisture
from the skin. The use of cotton in any form is not recommended.
Cotton attracts moisture and retains it close to the skin
making this problem worse. Wet cotton has been documented
to increase heat loss by up to five times.
Respiration
is the heat lost into the environment by active exhalation.
While this is a normal physiological body action, this loss
can be limited through the use of heated/humidified oxygen.
This prevents the body from having to warm the air inhaled
with each breath.
It is
important for all cavers to dress in layers. Polypropylene
and other synthetic materials are recommended as they wick
moisture away from the skin and help in the retention of
body heat. Other items such as neoprene socks offer the
caver protection from the streams so often encountered underground.
Keeping feet dry helps them stay warm.
The
equipment carried in packs can make the difference between
staying warm or needing assistance to exit the cave, should
the party have to stop for any extended period of time.
Emergency items should include a large, heavy-duty lawn
trash bag, a candle, food (high in complex carbohydrates),
and fluids with the correct electrolyte balance such as
sport drinks, like Gatorade for example.
Diagnosing
Mild to Moderate Hypothermia Without a Thermometer
While
most clinicians and EMS providers take something as simple
as the measurement of a patientís temperature for granted,
the initial responders in a cave rescue often lack the equipment
needed for such a measurement. The initial response team
(IRT) is sent into the cave for a hasty search. This search
is designed to rapidly cover a large portion of the likely
areas of patient location. This is accomplished best if
the rescuers travel light and carry only very basic equipment.
Once the patient is located, a medical team is dispatched
and the proper equipment is sent underground.
The
IRT must rely on the presenting signs and symptoms to recognize
and identify a potentially hypothermic patient. As hypothermia
develops, the patient moves from mild to moderate stages.
These changes may be detected by noting the change in patient
behavior. If the IRT can identify the patientís problems
and relay that information to the medical officer, the medical
team can be better prepared for treating the patient and
plan for the level of urgency necessary.
Patient
Temperature Measurement
When
the medical team reaches the patient in a cave and finds
him/her in a moderate to severe stage of hypothermia, it
is important to establish a baseline temperature and have
some way to monitor it throughout the rescue. The most useful
form of measuring temperature is a core reading taken rectally,
but the typical liquid-in-glass thermometers are fragile
and not suitable for the rugged underground environment.
The electronic thermometer is the best choice. It does require
batteries, but the batteries are usually the same as the
ones used in helmet lighting, so spares are readily available.
The electronic method provides for constant monitoring throughout
the rescue. In recent years, readily available indoor/outdoor
electronic thermometers with a remote probe have been used
in cave rescue situations. (The use of rectal monitoring
requires that the provider use discretion in placement and
provide the patient some privacy from other rescuers during
the procedure.)
Field
Re-warming Concerns
Re-warming
victims of hypothermia in cave settings presents unique
problems. After the patient is packaged and readied for
evacuation, the medicís duties are far from over. During
the trip out of the cave, patient posture and positioning
are important. Hypothermic patients are prone to rapid drops
in cerebral blood pressure when positioned upright. Sudden
loss of consciousness and seizures have been reported. Therefore,
patients should be kept as level as possible during transport.
This concern is of great importance when vertical evacuation
are necessary or in an area of the cave where the Stokes
stretcher must be stood on end for space considerations.
Another
concern in severe hypothermia is cardiac fibrillation and
other dysrhythmias. The patient must be handled as gently
as possible, which can be difficult in the cave environment.
Rough handling ‚ as well as centrally invasive procedures
that stimulate the heart, and deep airways stimulation ‚
can precipitate ventricular fibrillation. However, invasive
procedures such as the initiation of IV lines or intubation
should not be withheld, as there is no documentation that
these limited procedures could harm the patient. (While
it is rare for medics to monitor for dysrhythmias in a cave
environment, they should be aware of them and able to identify
them when a cardiac monitor is available.)
The
first step is always to stop the loss of heat. Preventing
further heat loss can be done by the following means: creating
a warm environment, removing wet clothes and replacing them
with dry ones, using either a vapor barrier and wool blankets,
or the new style synthetic patient wraps that provide both
qualities with reduced weight, such as the DoctorDown hypothermic
wrap.
Secondary
Goal: Restoration of Normothermic Core Temperature
- Monitor
pulse, respiratory status, and blood pressure. Ensure
that remote access equipment is properly placed so that
when the patient is packaged there is no reason to expose
him or her every time a re-assessment is needed. For example,
use a one-handed blood pressure cuff that includes the
gauge and bulb in one piece and can be routed outside
the protective wraps. And use a remote placed stethoscope
such as the ones used in the operating suites for apical
monitoring.
- Monitor
core temperature in patients who present initially with
moderate hypothermia. A simple and rugged small electronic
indoor/outdoor thermometer with a remote probe works the
best.
- Do
not allow patients to exert themselves as this can worsen
their condition; sudden activity of a patient with cold
extremities may cause reflex vasodilatation and a rush
of acidotic blood to the core. This can cause ventricular
fibrillation. Generally, even mildly hypothermic patients
should not be allowed to climb or walk out of the cave
by themselves.
- Establish
IV access in patients with moderate hypothermia for fluid
replacement and for medication administration, should
medications be needed. Ideally, fluids given should be
pre-warmed to a "normal" patient temperature. However,
it is very important not to make the fluids too warm;
fluid administered at 112† F or warmer will cause cell
damage at the site of infusion.
- Fluids
should not only be preheated but should also be kept warm
while being administered. This can be accomplished by
using insulated/heated IV wraps and pressure bags. Since
often the IV must lie in the Stokes and canít be elevated
for gravity feed, it must be pressured infused.
- While
the actual re-warming from the warmed fluids is minimal,
such fluids prevent further heat loss. Cool fluids could
exacerbate the already compromised patient.
- Evaluate
blood glucose levels and administer IV glucose in hypoglycemic
patients to maintain normal levels. In mildly hypothermic
patients, oral nutrition and fluids may be used. Current
commercial carbohydrate gel products like PowerGel are
easily processed by the body and provide not only glucose,
but also complex carbohydrates. However, they need to
be accompanied by quantities of fluid because they can
induce dehydration.
- Insert
a Foley catheter in the moderate hypothermia patients.
This is especially important in patients with long evacuation
times because hydration and initial cold diuresis will
produce increased amounts of urine. Catheters also allow
for the monitoring of urine production.
- Administer
supplemental oxygen, if available. (While oxygen is vitally
important for the seriously injured/hypothermic patient,
because of its weight and bulk, it is often not available
in cave rescue situations. Oxygen should be warmed first.
As with fluids, while the actual re-warming realized through
the use of heated oxygen is slight, it prevents further
heat loss. Heated/humidified oxygen prevents further loss
by respiration. The large surface area of the lungs allows
for the rapid exchange of heat.
- Use
external heat packs in mild to moderately hypothermic
patients. Place them in key points such as the trunk,
groin, and abdomen to facilitate the re-warming process.
The extremities should be allowed to warm at their own
rate.
- Transport
the patient in a supine position in a Stokes stretcher
protected from sides and bottom impact. The patient should
be insulated in a vapor barrier and insulation layers
- plastic wrap and wool blankets or new synthetic wraps.
- Protect
the patientís head with a proper style, impact-resistant,
vertical helmet, and protect the eyes with goggles. Tent
the vapor barrier over the face with a SAM splint. The
tenting allows the barrier to be pulled down as necessary,
as when needing to cover the face from falling water.
- Be
as gentle in movement as possible.
- Keep
the patient as level as possible during transport to prevent
sudden decreases in cerebral blood flow. If the patient
must be turned vertical for a pit rescue, maintain close
monitoring of the patientís level of consciousness.
- Check
a pulse for a full minute before initiating CPR. In the
hypothermic patient, the pulse is slowed greatly, and
thus can be missed. A slow rate is appropriate in a hypothermic
patient, and CPR administered to a bradycardia patient
can initiate ventricular fibrillation.
- Follow
standard ACLS protocols in patients with core temperatures
above 86†F but exercise care in drug dosages and frequency
of administration.
Prevention
of Hypothermia in Rescuers
Rescuers
spending long periods underground must pace themselves and
be alert for early signs and symptoms of hypothermia in
themselves and in their comrades. Rescuers must maintain
their caloric and fluid intake on a routine basis while
underground and working on a task. Complex carbohydrates
and balanced sport drinks are the best items to carry and
consume.
Rescuers
assigned to fixed posts, communications or entry control,
for example, should ensure that their work area is out of
trunk passage or wet areas, and placed in alcoves or just
inside a side passage. They should also insulate the area
where they sit or work with Thinsolite or similar padding.
Exercising
and continued movement while working in a cave is also important.
However, shedding clothing or layers when feeling warmer
invites increased heat loss through radiation and convection.
With proper layering and garment materials, perspiration
will be wicked away from the body and not threaten rescuers
through further heat loss. Polypropylene and other synthetic
materials offer the caver much more protection in that they
wick moisture away from the body rather than hold it next
to the skin.
Being
prepared for and able to adapt to the cold, moist conditions
encountered underground is the best mental and physical
defense from becoming a victim of hypothermia. Proper equipment
and proper mindset are the most important attributes as
one descends underground.
Greg
is a Sergeant in the Amherst County, Virginia Sheriffís
Office and joined the Society in March 2001.
Wilderness
Medicine Letter,
Volume 18, Number 4, Fall 2001
