Hypothermia and the cave rescue environment
A review of treatment and
advanced prehospital provider care
December19th 2000
Greg
L. Turner
University
of Virginia
Department
of Emergency Medicine
In general, hypothermia is defined as having a core body temperature of less than 95 F (35 C)[2]. While most clinicians agree that a body core temperature of 95 F is the cutoff point for clinical diagnosis, there are varying degrees of hypothermia and the associated presenting signs and symptoms. The general classifications of hypothermia include acute, sub-acute and chronic[3].
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Acute – generally involves a quick, severe exposure such as cold water immersion Sub-acute – involves a generalized exposure in lowered ambient temperatures, such as the caves of Virginia Chronic – involves a prolonged and continuous exposure such as homeless persons, those without heat in lower income households and the elderly |
It is the sub-acute arena that this paper will explore. Within the sub-acute generalized category, there are three classifications of patients; mild, moderate and severe. These categories are based upon the general physiological response of the patient:
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Mild – 32 to 35 C (89.6 to 95 F); associated with shivering and an intense feeling of being profoundly cold, patient’s body attempts reversal by shivering, increased respiratory rate, vasoconstriction and increased basal metabolic rate Moderate – 26 to 32 C (78.8 to 89.6 F); shivering decreases and stops completely, metabolic rate decreases, vasoconstriction continues Severe – below 26 C (78.8 F); patient looses defenses for reversal of condition, greatly increased chance of a primary event ventricular fibrillation |
There are several generalized causes of hypothermia. They include decreased heat production, impaired thermoregulation and increased heat loss. Decreased heat production can be caused by several metabolic disorders such as hypoglycemia, endocrine disorders or the depletion of nutritional reserves. Impaired thermoregulation within an individual can be the result of a CVA, head trauma, and drug or medication usage. Lastly,
increased heat loss if generally attributed to environmental factors such as, the use of non heated fluids and oxygen on an otherwise stable patient, exposure to air flow in a cooled environment and an increased rate of water loss. It should also be noted that conductive heat loss is increased in a wet environment. Since many caves contain stream passage and standing water this is of particular concern.
There are several methods through which we loose heat to the environment. They include conduction, convection, radiation, evaporation and respiration. The patient in a typical cave rescue setting is faced with fighting all of these routes of heat loss.
Method Of Loss – Explanation - PreventionConduction – direct contact; insulate patient Convection – air draft; move from trunk passage Radiation – electromagnetic heat wave; cover patient Evaporation – moisture on skin; use wicking layers Respiration – active exhalation; heated oxygen |
Conduction is often one of the first to attack the victim as they have direct contact with cold surface such as the cave floor. This problem can be addressed by insulating patient with a thinsolate or similar pad under them. (It should be noted that the pads should be made of foam and not the air filled type, as air conducts the cold through to the patient) Rescuers cover victims with insulated materials, but often forget that the fastest way patients loose heat is through the floor they are in contact with.
Convection occurs when heat is lost through air movement over patient’s 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 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 normo-thermic 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, it is expected to build up skin moisture in the form of perspiration during normal activities. When the caver becomes immobile, this moisture can be a source for heat to be transferred to the environment. This form of heat loss can be lessened by wearing layers of clothing and ensuring that these layers wick moisture from the skin. It should be noted that 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 though the use of heated/humidified oxygen. This prevents the body from having to pre-warm the air inhaled with each breath.
There are a variety of routes of heat loss in the typical cave rescue patient. Careful monitoring of the patient and proper insulation will limit these losses and this is certainly the first step in the care of a hypothermic patient; stop the heat loss.
While most clinicians and EMS providers take something as simple as the measurement of a patient’s temperature for granted, the initial responders in a cave rescue will often lack the equipment needed for such measurement. The initial response team (IRT) is sent into the cave for a hasty search. This search is meant to cover a large portion of the likely areas of patient location in a rapid manner. In order to cover this large expanse of passage, they must travel light, thus only the very basics of equipment are present. As the patient is located, a medical team is dispatched and the proper equipment sent underground.
However, for the IRT to recognize and identify a potentially hypothermic patient they must rely on the presenting signs and symptoms. If the IRT can identify the medical problems they will face with the patient, then relay the information to the medical officer, he can more rapidly prepare for and facilitate treatment of the patient.
The presenting signs and symptoms of hypothermia vary with the classification and individual, however generally recognized items to note include:
q A patient complaining of a generally lowered temperature
q Shivering in mild to beginning moderate cases (will disappear as the moderate case progresses to severe)
q Ataxic gait
q Slurred speech
q Blank stare
q Difficulty in concentrating and general apathy
q Impaired fine motor movement, i.e. use of fingers in tasks such as tying boot laces or knots in rope work
q Confused or unclear thought processes
q Fatigues easily
Remember that shivering is found only in mild to beginning moderate hypothermia and may be suppressed with depleted glucose stores or physical exertion [4]
Differentiating between moderate and severe hypothermia without a thermometer
As the hypothermia develops, the patient moves from the mild to moderate stages. These changes may be detected by noting the change in patient behavior. If the medical staff is not yet on scene, it is very important that these changes be forwarded to the medical officer so he can prepare for a change in the patient treatment plan and urgency of evacuation.
Some of the outward signs and symptoms to be aware of include:
q Lethargy
q Decreased pulse rate
q Decreased respiratory rate and effort
q Muscle tone increase (as the patient becomes increasingly hypothermic, the muscle tone will increase and may actually mimic rigor in advanced cases)
q Mental status changes / loss of consciousness
Several factors make an individual more susceptible or pre-disposed to hypothermia. These pre-disposing factors are wide ranging and should be explored when developing a working history for potential patients in a search or from the patient themselves when involved in a rescue.
Alcohol – causes surface vasodilatation, which increases the rate of heat loss. It predisposes the patient to hypothermia because the patient may extend their risk taking behavior. Ethanol also acts in a limited manner to suppress shivering and further create factors to pre-dispose patients because they have limited their ability to produce heat through exhaustion, fatigue, dehydration, and decreased caloric intake.
Diabetes – hypoglycemia can exacerbate hypothermia because the stores of glycogen are often limited [5]
Hypothyroidism – affects the metabolic rate and thus the rate at which the body would be able to generate heat
Medication use – narcotics, benzodiazepines, phenothiazines, tricyclic antidepressants, chlordiazepoxide, antipsychotics, and other similar medications affect not only the basal metabolic rate, but also act to suppress the shivering mechanism
In general, anything that lowers the body’s store of energy, glycogen or otherwise interferes with heat generating mechanisms, can predispose one to hypothermia. [6] Chronic medical conditions or the medications used to treat them such as diabetes, seizures, cardiac, and hypertension all may work to make a patient more susceptible to hypothermia.
When the medical team reaches the patient and finds them in a moderate to severe form of hypothermia, it is important to establish a baseline temperature and have some way to monitor it throughout the rescue.
In reviewing the methods of measurement, it should be noted that oral and axillary methods record a reading lower than the actual patient core temperature. The most useful form of measurement is a core reading. This form of measurement can most easily be taken rectally in the cave setting.
Several methods of core measurement are available, rectal, esopogheal, and tympanic membrane. The rectal method is generally the simplest, most accurate and least expensive method of use. While the infrared tympanic membrane measurement is the least intrusive, it does depend on expensive fragile equipment that can’t stand up to the rigors of underground medicine. Other factors such as direction of the external ear canal and the presence of earwax or debris will make tympanic measurement inaccurate.
The method used to obtain the rectal measurement is as important as the route chosen. The typical liquid-in-glass thermometers break easily and are simply not suitable for the rugged underground environment. The electronic thermometer is the best choice. It does require batteries, but they most often are the same as the ones used in helmet lighting so spares are readily available.
The use of rectal monitoring does require the provider use discretion in placement (provide the patient some privacy from other rescuers during the procedure). This method does however provide for constant monitoring throughout the rescue with inexpensive readily available equipment. Readily available supplies such as an indoor/outdoor electric thermometer with a remote probe have been successfully used in cave rescue situations for years.
Other methods of measurement such as color change chemical strips such as temp-a-dots are not useful as they only reflect the skin temperature not the true core temperature. Some texts offer reference charts that attempt to correlate signs/symptoms and temperature are not an accurate method of measurement because of wide variances in patients and their individual response to environmental exposure.
Hypothermic effects on the cardiac, respiratory, and central nervous systems.
Following exposure, an individual can maintain their body temperature through several compensatory mechanisms. Shivering can generate about 500 kcal/hr; this is done through muscular contractions of about 6 to 12 cycles per second [7]. Shivering is initiated by the body through the hypothalamus as the core temperature begins to drop below 98.6 F (37 C). Shivering can be stopped by one of four methods; the patient temperature drops below 86 F (30 C), the temperature rises above 98.6 F (37 C), hypoglycemia begins and there are insufficient energy store to sustain shivering or medications inhibit the inherent process of shivering.
When the patient becomes hypoglycemic, the hypothalamus stops the shivering process. Thus it is important to maintain the patient’s fluids and caloric intake. It is generally agreed in most research that the body begins to centrally inhibited shivering when blood glucose levels fall below 45mg/dl. [8]
While shivering does raise patient temperature, it is not an efficient form of re-warming. It may shunt warmed blood from the core to the periphery, as they are the main muscles involved in movement during the shivering process. Vasodilatation also occurs in the skin of extremities. As shivering increases it also creates more demand on the body, drains more of the glycogen stores, and increase oxygen demand and cardiac workload, as well as myocardial oxygen consumption. While it has been noted that shivering is an ineffective from of re-warming, it should also be noted that it accomplishes what little re-warming it does attain at great expense to the body. Therefore support in the form of fluid replacement and caloric intake are important for any patient who has been shivering for a prolonged period of time.
Upon exposure, the body responds through vasoconstriction in the periphery, increase the heart rate and respiratory rate; increase in blood pressure and basal metabolic rate due to an immediate release of catecholamines. As the patient remains exposed, these initial increases will begin to fall and eventually fail, throwing the patient into moderate to severe hypothermia. The “general decline in the physiologic responses after the initial catecholamine response has waned, the respiratory rate begins to decline slowly, and the pulse rate and blood pressure now decreases” [9] As noted, one of the greatest threats to the patient in progressively advancing hypothermia are the cardiovascular decompensation in both conduction and ventricular irritability [10] Several studies agree that as the patient becomes increasingly hypothermic, at about 82.4 F (28 C) the patient is susceptible to spontaneous ventricular fibrillation and apnea.
When discussing re-warming, there are two avenues to review, active and passive. Active re-warming refers to adding enough heat to make the core temperature rise appreciably. Passive re-warming refers to insulating the patient and allowing the patient’s basal metabolic rate and shivering to raise the core temperature.
Within the active re-warming classification, there are two general categories; core and surface warming. Core warming affects the core of the body before the extremities while surface re-warming affects the skin and limbs first then moves toward the core.
When considering any re-warming activity, there are three major complications to be aware of: temperature after drop, re-warming shock and sudden death. After drop is associated with the fact that the core temperature often drops several degrees when re-warming is first initiated because the blood in limbs and skin is cooler and moves to the core, thus cooling the core initially. After drop is a potentially significant complication because of the metabolically acidotic products that are shunted to the core. Re-warming shock is associated with severely hypothermic patients and is associated with relative hypovolemia as a result of vasodilatation during re-warming and accompanying dehydration. The importance of rehydration during resuscitation and evacuation is stressed here as a preventative measure. Sudden death is also often associated with severely hypothermic patients and has been associated antidotaly to ventricular fibrillation and re-warming shock but no studies have verified specific causes. Recommendations to help prevent this sudden death phenomenon are to administer warmed IV fluids to assist in preventing re-warming shock, to warm the core first to prevent after drop and to consider the prophylactic treatment of ventricular fibrillation through pharmacological agents [11]. The agent of choice in the past has been Bretylium as most studies have shown. However the recent limited availability of this medication precludes this option and studies have shown that the use of lidocaine or procanamide are not only less effective in hypothermia, but contraindicated due to detrimental patient outcome in studies conducted. [12]
The most dangerous period for any hypothermic patient is the re-warming phase. Closely monitored patients within the confines of special care units in the clinical setting often experience sudden death, so field treatment is best limited to moderate and mildly hypothermic patients and carefully supervised and monitored by the field medic. One of the most dangerous situations is for the severe to moderately hypothermic patient to be surface re-warmed only and the resulting shunt of cold blood to the core and release of metabolic wastes into the core are devastating to the patient who is already ill and in a threatened condition. Thus close adherence to the recommended protocol is required to prevent the re-warming of the surface before the core.
After the patient is packaged and readied for evacuation, the medic’s duties are far from over. During the trip out of the cave, patient posture and positioning are important to note. It should be noted that hypothermic patients are prone to rapid drops in cerebral blood pressure when positioned upright. Sudden loss of consciousness and seizures have also been reported in this patient population, therefore the patient should be kept as level as possible when transporting.[13] This concern is of great importance when you are faced with a vertical evacuation or in an area of the cave where the stokes stretcher must be stood on end for space considerations. It should be noted that some research recommends the use of MAST in these special circumstances to maintain cerebral blood flow, but this is a controversial area and is omitted and not recommended here.
Most active re-warming techniques for the severely hypothermic are beyond the capabilities of paramedical staff. Methods such as gastric and urinary bladder lavage, peritoneal lavage with warmed dialystate, hemodialysis with heat exchanger, cardiopulmonary bypass or thoracotomy with lavage of the mediastinum are active aggressive measure utilized within appropriate clinical environments. Field intervention should be limited to the prevention of further heat loss and supportative measures. Cases of severe hypothermia are best left to the clinicians in the controlled hospital setting. However, in remote long term evacuations, medical control should be established with your team’s wilderness medical control physician and in consult with the medical control physician at the receiving facility. This team may order further treatment based on the patient’s condition and evacuation time expected.
It should be noted that the wilderness medical control physician may be in another area of the state or an adjoining state and can provide advanced care and treatment recommendations to both the field medic and the receiving facility physician as to the capabilities and restraints faced by the medic working in the cave environment.
In reviewing the differences between active insulation and spontaneous re-warming we need to explore the basic definition of each. Spontaneous re-warming begins naturally once the heat loss has stopped, unless the patient has progressed so far toward severe hypothermia that all regulatory mechanisms are in failure.[14] On the other hand, active insulation refers to the act of blanketing the patient with warmed air; coverings and insulating him from further heat loss [15] Both are very important treatments in the care of a mildly hypothermic patient, however the patient in moderate hypothermia needs further care and assistance.
Passive re-warming is very slow and depends on the patient’s ability to shiver. Since the average patient is only able to produce about 70 kcal/hr and this is reduced with lowered core temperature and metabolic rates this is not the re-warming method of choice in any but the very mild cases. Obviously those patients in moderate to severe hypothermia would not benefit at all from a passive re-warming attempt, as they are unable to shiver and re-warm themselves at all.
Advanced life support modifications in a hypothermic patient
Hypothermic patients do not respond to advanced care in the same manner as normothermic patients and modifications must be made in the care offered to these patients. It should be further noted that severely hypothermic patients often do not respond at all to standard ACLS measures.
Patients in the moderate to severe hypothermic area, 82.4 to 86 F, may present with refractory ventricular fibrillation not able to be controlled with either electrical defibrillation or pharmacological treatment.
While fibrillation is a concern, other cardiac abnormalities are often present in hypothermic patients. ECG changes such as J waves are often seen on the down stroke of the QRS. Disryhmithias such as spontaneous atrial fibrillation is also prevalent in patients below 86 F. This run of atrial fibrillation often resolves itself upon re-warming. While it is rare that the medic is able to monitor for these disrhythmias in a cave environment, they should be aware of them and able to identify them when the patient is accessible to a cardiac monitor. The major note to be learned here would be the importance of handling the patient gently. It has been documented that rough movement, centrally invasive procedures that stimulate the heart or deep airways stimulation may precipitate ventricular fibrillation. It is important to note however that 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 moderately hypothermic patients often have increasing respiratory depression, respiratory acidosis often occurs as a result of the increase in carbon dioxide retention. One important note concerning the respiratory status often overlooked is a left shift of the oxyhemoglobin dissociation curve (the hemoglobin is more tightly bound to the oxygen and the carbon dioxide is more readily dissolved in the serum) [16]
As the patients heart rate falls, so too does the cardiac output and the patient becomes increasingly hypotensive. As the core body temperature drops, so too does the patients level of consciousness, it is noted that for every 1 C the patients temperature drops, there is an associated 6 to 7% decrease in cerebral blood flow.[17] The patient will also have a decrease in glomerular reabsorbsion and a subsequent increase in urine flow this is known as cold dieresis and can lead to marked dehydration.[18] In addition to the cold diuresis phenomenon, patients also shift fluid from the intravascular space to interstitial spaces and thus require even more aggressive fluid resuscitation than a normally dehydrated patient.
Medication administration in the hypothermic patient must be carefully monitored. While the patient is moderately to severely hypothermic, the circulation and absorption of medications is reduced. Thus, as the patient warms up, the medications are more rapidly absorbed and an effect of a medication bolus is realized. This can have a serious untoward effect on the patient.
With regards to airway management, the criteria for intubation are the same for a hypothermic patient as for a norma-thermic patient
While this is only a model policy (and is meant only for instructional purposes) this protocol may be presented to your agency OMD or wilderness OMD for review and inclusion within your standing orders as they may determine appropriate.
The first step is always to
stop the loss of heat.
Prevent further loss through insulation, create a warm environment, remove wet clothes, replace with dry ones, use either a vapor barrier and wool blankets, or the new style synthetic patient wraps that provide both qualities with reduced weight
The secondary goal is to restore normothermic core temp.
1. Monitor pulse, respiratory status, and blood pressure (ensure that remote access equipment is placed as the patient is packaged to prevent having to expose patient every time a re-assessment is needed)
2. Monitor core temperature in patients who present initially with moderate to severe hypothermia (a constant monitor such a digital rectal probe is recommended)
3. No exertion, do not allow the patient 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; which can also cause ventricular fibrillation) Thus the patient should not only not be allowed to exert themselves, but not to walk or climb out.
4. Establish IV access for patients in moderate hypothermia for fluid replacement and medication administration if needed, any fluids given should be pre-warmed to a “normal” patient temperature (however it is very important to not heat these fluids too warm as fluid administered at 112 F or warmer will cause cell damage at the site of infusion), it is important to not only pre-warm fluids, but to keep them warm while being administered, this can be accomplished by using insulated / heated IV wraps and pressure bags, (since the IV must lie in the stokes and can’t be elevated for gravity feed, it must be pressured infused) (it is important to note that while the actual re-warming noticed through warmed fluids is minimal, it is very important to remember that the pre-warmed fluids prevent further heat loss in the patient by receiving cool fluids which will certainly exacerbate the already compromised patient)
5. Evaluate blood glucose levels and administer IV glucose in patients to maintain a normal level, in mildly hypothermic patients, oral nutrition and fluids may be used. Current commercial products such as Power Gel are easily processed by the body and provide not only glucose, but also carbohydrates. It should be noted however that products such as Power Gel need be accompanied by quantities of fluid as they in themselves can induce dehydration.
6. Place a foley catheter in the moderate hypothermia patients (this is important in patients with long evacuation times since hydration and initial cold disuresis will produce increased amounts of urine, it also allows for the monitoring of urine production)
7. As available in the cave environment, administer supplemental oxygen, if it is administered though, it must be warmed first (it is recognized that the extra weight and bulk that this will add to the rescue effort, but it is vitally important in the critically injured/hypothermic patient) While the actual re-warming realized through the use of heated oxygen is slight, it is important to note that 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 and thus supplemental warmed oxygen is typically administered, even though the exact rate of warming benefit has not been clearly documented [19]
8. In mild to moderately hypothermic patients, external heat packs may be used in certain key points such as the trunk, groin, and abdomen to facilitate the re-warming process. (these core areas should only be warmed and the extremities left to warm on their own at their own rate) [20]
9. Transport 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). The head should be protected with a proper style impact resistant vertical helmet and the eyes with goggles. Finally, you should tent the vapor barrier over the face with a SAM splint. This tenting around the face allows the barrier to be pulled down when needed to cover the facial area in areas of falling water such as waterfalls etc.
10. Prevent rough handling of the patient. Be as gentle in movement as possible.
11. No tilting. Make sure the patient is kept as level as possible. (by keeping the patient in as near a level transport position as possible, you can prevent sudden decreases in cerebral blood flow, if the patient must be turned vertical for a pit rescue, close monitoring of loc must be maintained, some research recommends the use of MAST in these circumstances, but this is a controversial area and is omitted here)
12. Bradycaridia is an expected response to hypothermia and should not be treated in a patient with a pulse.
13. As needed, standard ACLS protocols may be followed in patients with core temperatures above 86 F (30 C), but care must be exercised in drug dosages and frequency of administration.
14. CPR, it should be noted that you should check a pulse for a full minute before initiating CPR. In the hypothermic patient, the pulse is greatly slowed, and thus can be missed of you do not check for the full minute. A slow rate is appropriate in a hypothermic patient, and CPR administered to a bradacardiac patient can initiate ventricular fibrillation.
All rescuers must dress properly in layers that wick moisture away from the body. It is important to pace yourself, and be alert for early signs and symptoms not only in yourself but also in the others within your group. Replenishment of fluids and nourishment in rescuers is required and must be done on a routine basis while underground and working on task.
For those assigned to fixed posts, such as communications or entry control, you should ensure that their work area is out of trunk passage or wet areas, and placed in alcoves or just inside a side passage. You should also ensure that the area is insulated where they sit or work with thinsolite or similar padding.
Exercise, and continued movement while working in a cave is important. However, it is always important to note that you should not shed clothes or layers as you warm up as this invites increased heat loss through radiation and convection. If you are using the proper layering and garment materials, perspiration will be wicked away from the body and not threaten the rescuer through further heat loss.
[1] Sloan, Noal MD, Injuries Underground The Ultimate Sport The Most Challenging Patient, lecture notes NCRC 1999
[2] Stewart, Charles E. MD, Environmental Emergencies, 1990, pg 91
[3] Conover, Keith MD et all, Wilderness EMT Lesson Plan, 1994, pg IX-17
[4] Stewart, Charles E, MD, Environmental Emergencies, 1990, pg 93
[5] Freinkel N Metzpen BE, et all, The hypothermia of hypoglymcia, N Engl J Med, 1972; 287:841-5
[6] Universal Study Guide for Cave Rescue Training, NCRC, 1993, pp 18-5
[7] Stewart, Charles E, MD, Environmental Emergencies, 1990, pg 95
[8] Hanson, PJ , et all, Hypothermia in hypoglycemia, Br Med Jr. 1984: 288; 1212-1213
[9] Stewart, Charles E, MD, Environmental Emergencies, 1990, pg102
[10] ibid pg 102
[11] US Army Research Institute of Environmental Medicine. Medical afteraction conference, Mount Hood 1986 bypass rewarming. Report # T10-88. U.S. Army Medical Research and Development Command Natick MA, 1988
[12] Angelakos, ET, Hengnauer AH; Pharmacological agents for the control of spontaneous ventricular fibrillation under progressive hypothermia; Journal Pharmautical Therapy 1959; 127:137-45
[13] Universal Study Guide for Cave Rescue Training, NCRC, 1993, pp. 18-9
[14] Universal Study Guide for Cave Rescue Training, NCRC, 1993, pp 18-8
[15] ibid 18-8
[16] ibid pg 103
[17] ibid pg 103
[18] Conover, Keith MD et all, Wilderness EMT Lesson Plan, pg IX-17
[19] Slovis, CM, Bachvarou HL; Heated inhalation treatment of hypothermia; American Journal of Emergency Medicine; 1984; 2:533-534
[20] Miles, JM Thompson GR, The Treatment of severe accidental hypothermia in children, Am Journal of Emergency Medicine 1985; 3:38-41