An average of 700 people die from hypothermia in the United States annually. Half of those who die are older than 65 years of age.

- Environmental Hypothermia is caused by cooling from conduction, convection, evaporation, resperation and radiation.
Most heat is lost thru radiation. Wet clothing will greatly increase conduction of heat away from your body. Wind chill is also an important factor.

- Drug-induced hypothermia is usually due to ethanol alcohol that causes vasodilation, insulin and other hypoglycemic agents. Beta blockers or antipsychotics can also predispose a person to hypothermia.

Signs and Symptoms of hypothermia. There are several classification systems; The most common three level model is:
Mild hypothermia - 90-95°F
Moderate hypothermia - 82-90°F
Severe hypothermia - < 82°F (28°C) [Some classify severe as < 86°F (30°C)]

Emergency help should be called for when a person's body can no longer compensate for hypothermia (shivering stops) or if there is no warm environment it can be reversed. The critical point can vary based on individual metabolism, but usually occurs when core temperature reaches 92-89 deg. Emergency Care and Transportation (9th ed. American Academy of Orthopedic Surgeons)

Core Temp	Signs And Symptoms	Cardiorespratory Response	Level Of Consciousness
95-90	Shivering, Foot Stamping	Constricted Blood Vessles, Rapid Breathing	Withdrawn
92-89 *	Loss of Coordination, Muscle Stiffness,	Slowing Respirations, Slow Pulse	Confused, Lethargic, Sleepy
88-80	Coma	Weak Pulse, Arrhythmias, Very Slow Respirations	Unresponsive
<80	Apparent Death	Cardiac Arrest	Unresponsive

* Note they overlap the first two categories 90-92 can be in either.

EMT Prehospital Emergency Care 8th edition (Pearson Education)

Core temp		Condition
°F	°C
98-95	37-35	Cold Pale skin The patient is alert, shivering	Poor muscle coordination. Rapid breathing Rapid heart rate.
95-90	35-32	Cold, waxy skin. Puffy face, possibly pink. No shivering.	Confusion. Muscle rigidity. Slow heart rate.
90-86	32-30	Dialated pupils. Diminished reflexes. Stupor or coma.	Rigid muscles.. Slow breathing rate. Hypotension. Slow heart rate
86-82	30-28	Fixed dilated pupils. Coma. Flaccid muscles.	Slow respiration. Slow or rapid heart rate. V-fib, Possible cardiac arrest.
82-68	28-20	Cyanosis. Fixed, dilated pupils. Unresponsive.	Barely detectable vital signs. Irregular pulse. Cardiac arrest.

The Swiss classification adds levels.

Swiss system with 5 levels.

Stage	Condition	Core temp °F
I	The patient is alert, shivering, rapid heart	95-90
II	The patient is somnolent (drowsy) and confused, not shivering, slow heart rate	90-86
III	The patient is unresponsive	86-82
IV	Absent vital signs, apparent death (thorax compressible, pliable abdominal muscles)	82-75
V	Death (non-compressible thorax, rigid abdomen)	75-59

Source: Avalanche Emergency, RemoteEmergencyCare.com

One other system

Core temp		Condition
°F	°C
97	36	Shivering begins
93	34	Tachycardia, then bradycardia amnesia, dysrhythmias
90	32	Shivering almost gone, stupor
86	30	atrial arrhythmias, low cardiac output, muscular rigidity
84-82	28-29	paradoxial undressing, V-fib risk
72	22	unconciousness

The typical progression is from sinus bradycardia (slow <60 heart rate) to atrial fibrillation with slow ventricular response, to ventricular fibrillation (V-fib), and ultimately to asystole (flatline - no cardiac electrical activity).

Heart rate and respirations will initially increase, but will begin to decrease with temperature.
At 93° the carbon dioxide production begins to decline as the cell metabolism slows down drastically. Carbon dioxide is the major stimulus to breath, so the respiratory rate and tidal volume will decrease and eventually become ineffective.

Skin will be red at first then turn pale, then cyanotic (blue-gray), then gray.

A thermomater that records a broad range is required. Feel the abdomen for a general impression of core temperature.

Carotid and radial pulses may be difficult to find on the severely hypothermic patient.

One source Hypothermia can be considered a type of hypovolemic shock (inadequate perfusion) which has two stages.
Stage I - Compensatory - Body compensates with increased heart rate, normal or slightly decreased blood pressure, slightly increased respiratory rate.
Stage II - Decompensated (Uncompensated) - Body looses its ability to control temperature. In shock from blood loss, heart rate and respiration will increase while with hypothermia they will decrease.

SOLO's Field Guide to Wilderness First Aid

• 98.6 F normal
• 97 F the brain falters, judgment fails, protective and survival instincts decrease.
  You get the "umbles": Grumble, stumble, mumble, bumble, fumble.
• 96 F shivering begins , a constant fine motor tremor .you cannot stop it. It interferes with coordinated muscle activity.
• 94 F You shiver harder; coordination is failing; you begin tripping and falling.
• 92 F Shivering is intense; you are unable to walk.
• 90 F Siivering is convulsive; you assume the fetal position; you are unable to talk.
• 86 F and below: The "Metabolic Icebox". you are unconscious , ashen gray; you may appear pulseless and breathless.

• Remove patient from cold environment.
• Do not allow the patient to walk.
• Remove any wet clothing and cover with blankets.
• Handle the patient gently.
• Do not massage extremities or allow patient to eat or to use any stimulants
• Give warm, humidified oxygen.
• Assess pulse for 30 to 45 seconds before considering CPR.
• Begin passive rewarming.
• Consult medical control.

• The first half hour during rescue is the most critical phase of hypothermia management.
• If the patient is responsive, gather a SAMPLE history. It is important to document pain or other symptoms and determine if the patient is using any medications, especially drugs (e.g. Beta blockers) or alcohol that might depress the central nervous system or cause blood vessels to dilate.
• Gentle Handling is important to avoid cardiac dysrhythmias such as V-fib, when patients get to the moderate to severe range.
• Keep them horozontal, avoid any jarring movements, and try to move axially (feet or head first) whenever possible.
• Don't massage or rub the person. Handle people with hypothermia gently; their skin may be frostbitten, and rubbing frostbitten tissue can cause severe damage.
• Rewarming of a severely hypothermic person must be gentle.
• It used to be thought that insertion of nasal or oral airways would precipitate cardiac dysrhythmias such as ventricular fibrillation (V-fib), but this belief is falling into question now.
• In a wilderness setting, do not evacuate a severely hypothermic person by hand, since the jolting and jarring of the journey severely risks ventricular fibrillation. Instead, send a rescuer out to arrange a helicopter evacuation and to consult with medical professionals about other rescue options.
• Even if the person seems dead to you, treat for hypothermia since his or her abnormally slow and weak pulse and breathing may fool you into thinking that they have stopped entirely. An old adage goes: "No one is dead until warm and dead."
• Guidelines for CPR vary.
  Make sure you do a complete assessment of heart rate before beginning CPR. Remember, the heart rate may be 2-3/minute and the breathing rate 1/30 seconds. Instituting cardiac compressions at this point may lead to life-threatening arrythmias.
  Check for any body movement or respiratory effort, both of which are lacking in a heart attack victim, and feel for a carotid pulse (in the neck, to the side of the windpipe) for a full minute before initiating CPR.
  Most guidelines say to go ahead with CPR, others assume you cannot detect a slow weak heart and say "Do not perform CPR, even if you think the heart has stopped."
  Altitude.org says "CPR is only recommended if swift evacuation to a medical facility is possible as once it is commenced it must be continued until the patient's heart can be monitored with an ECG.'
• In case of V-fib, defibrillate three times, if unsuccesful do CPR and rapid rewarming, resume defibrillation when temp reaches 86°F.

• Passive rewarming includes removal from cold environment and insulation.
  Remove wet clothing.
• Active external rewarming includes warm water immersion , heating blankets, set at 400C, radiant heat, forced air.
  Disadvantages are that is innefective with poor peripheral circulation, causes topical vasodilation leading to rewarming shock, can increase lactic acid thus leads to increase in metabolic demands.
  Hypothermia at MayoClinic.com says: Don't apply direct heat. Don't use hot water, a heating pad or a heating lamp to warm the victim. Instead, apply warm compresses to the center of the body - head, neck, chest wall and groin. Don't attempt to warm the arms and legs. Heat applied to the arms and legs forces cold blood back toward the heart, lungs and brain, causing the core body temperature to drop. This can be fatal.
• Body temperature should not be increased more than 1°F per hour.
• Oxygen should be warmed and humidified if possible.

Terms:
Beta Blockers - Drugs such as Inderal, Lopressor, Toprol XL, Visken, which are used to treat abnormal heart rhythm, high blood pressure, heart failure, angina (chest pain), tremor, and migraines.
They primarily block β1 and β2 receptors on cells. By blocking the effect of norepinephrine and epinephrine, beta blockers reduce heart rate; reduce blood pressure by dilating blood vessels; and may constrict air passages by stimulating the muscles that surround the air passages to contract.
See: Beta Blockers Drugs on MedicineNet.com

Links:
Hypothermia Prevention, Recognition and Treatment
Outdoor Action Guide to Hypothermia & Cold Weather Injuries
Hypothermia, Prevention, Recognition, Treatment: Hypothermia Special Situations.
Emergency Department Critical Care - Hypothermia at EMCrit.org
Rick Curtis, Outdoor Action Program at Princeton
How to Treat Severe Hypothermia | eHow.com
Avalanche Emergency - Rescuers 8
Diagnosis and Treatment of Hypothermia - December 15, 2004 - American Family Physician
Hypothermia: eMedicine Emergency Medicine
Hypothermia - Guidance for Trainers at RemoteEmergencyCare.com
Hypothermia at altitude.org
Hypothermia: First aid - MayoClinic.com
Hypothermia - What are the signs and symptoms of hypothermia on MedicineNet