H: Hypothermia

Hypothermia occurs when the body's core tissues become cold; usually 95 degrees F (35 degrees C) or colder.

(Core body tempuratures are usually measured in the rectum, esophagus, or bladder)

Low body tempuratures inhibit cellular metabolism, and cardiac arrest can result if optimal tempuratures are not restored.

Normally when I think of hypothermia, I think of exposure to extremely cold elements (like freezing water or snow) being the cause. But I live in the desert and the only times I've ever seen it is in people suffering from alcohol overdose. It is also a risk in people suffering from sepsis, when the thermo-regulation mechanism in the body has failed...or in the homeless population. In general, people who are ill, exposed, and cannot meet their own needs are at risk.

(Optimal body tempurature is usually 97.7-99.5 degrees F.)

There are four degrees of Hypothermia. Depending on the severity, the patient will need to undergo rewarming measures:

Mild: 90-95 degrees F. (Passive rewarming, remove cold or wet clothing and apply dry and warm covering. Allow patient's body provide it's own warmth)
Moderate: 90-82 degrees F. (Active external rewarming, forced air device over body or heat packs to underarms and groin...if you wanna be getto like that ;))
Severe: 82-68 degrees F. (Active internal rewarming, warm IV fluids I believe at a temp of 100.4 degrees F is recommended, but I'm not positive)
Profound: < 68 degrees F

I mentioned above that cardiac arrest can occur in hypothermia because cellular metabolism is inhibited. Because the cells have stopped working, any drugs you give the patient when the body tempurature is extremely low will not work. This is a concern because if a patient is extremely cold (below room temp) and is recieving CPR, the drugs given as part of ACLS protocol won't have any effect. (The defibrillation shock probably won't work either)

Partly because of this, a patient cannot be declared dead until the body has been warmed to at least room tempurature, and cellular metabolism has been given the chance to resume.

There is a treatment called therapeutic hypothermia in which the body tempurature is lowered to 91 degrees F.after a period of hypoxia or stress, your hospital will have specific protocol for when and how to use this treatment.