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

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
13. Be as gentle in movement as possible.
14. 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.
15. 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.
16. 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