Injuries due to exposure - Hypothermia


In temperate weather, the human body naturally regulates its core temperature to an average of 37°C, though an individual's actual core temperature may vary.

Hypothermia — which means your body temperature drops well below normal — can result when you're in an environment with a temperature much lower than the normal range. Hypothermia is defined as a core temperature below 95°F (35°C). Exposure to a cold environment results in your body losing heat faster than it's producing heat — at a rate that is affected by the temperature gradient between your skin and the environment, the heat capacity of the environment (this is much greater for water than for air), the presence of wind or water movement (such as tides or currents, both of which hasten cooling), your body composition (a higher lean-to-fat ratio and a lower body mass-to-surface area ratio both hasten cooling), and how much protective clothing you're wearing.

Hypothermia often occurs due to immersion in cold water, because water conducts heat away from the body 20 to 27 times faster than air. The shock if you're suddenly immersed in water colder than 59°F (15°C) — without thermal protection — can cause an inhalation gasp response, which can induce you to inhale water. The stress response also triggers an extremely rapid heart and breathing rate. In addition, cold shock may be accompanied by pain and mental disorientation, which can lead to fear and panic.

Good thermal protection — a wetsuit, drysuit or other survival-type gear — will dramatically lessen the immediate effects of immersion in cold water, but heat loss will still occur over time.

The rate at which your body produces heat can be increased by exercise or shivering, but if you are immersed in water and are wearing little or no thermal protection, swimming actually increases your exposed surface area and thus elevates the rate at which your body heat is transferred to the water. In general, you can maintain your core temperature by swimming only in water that's warmer than 75°F (24°C). An unprotected swimmer's core temperature will usually drop in water colder than that. An inability to continue swimming (a condition known as swimming failure) typically develops more rapidly than one expects in cold water.

If you are immersed in cold water and not wearing thermal protection, but have buoyancy support (such as a life jacket) and there is a chance of rescue, you should remain still in a position that minimizes your exposed surface area. Pulling your knees together and up to your chest is known as the heat-escape-lessening position (HELP), or the rescue position, and provides improved protection of the body's high-heat-loss areas: the armpits, groin, chest and thighs.

Immersion-related hypothermia can also occur in relatively warm or even tropical waters as a result of slow body cooling over time. This may happen if you're in water as warm as 84°F to 91°F (29°C to 33°C) if you're not wearing any thermal protection. In such circumstances, you may not be aware of the slow heat drain for some time.

Hypothermia can, of course, also occur in surface or land settings. The same factors — including the temperature of your environment, the presence of wind, and how appropriately you're clothed for the conditions — are key in whether, and how soon, you're likely to develop hypothermia. Similarly, even a slightly cool temperature can result in cold stress, depending on an individual's age, health status, body-fat ratio and body mass.

Signs and symptoms: (Symptoms of a disease are subjective indications that can be detected by a patient, such as pain or fatigue, while signs are objective indications that can be detected by a doctor, such as temperature or pulse.) The signs and symptoms of cold stress vary, according to how severe the condition is. The following chart details the signs and symptoms of various gradations of hypothermia.

Treatment: Individuals with mild hypothermia will be awake, conversing lucidly, complaining about the cold and probably shivering. Assuming no other injuries, mildly hypothermic victims can be rewarmed with a variety of passive or active techniques, with minimal risk of complications. If travelers suffer hypothermia in a remote setting, many rewarming options, particularly more aggressive and invasive techniques, will likely not be available; nevertheless, rescuers must do what they can to protect victims from further injury. The essential first step is, if possible, to remove any wet clothing and replace it with a dry insulating inner layer and a windproof outer layer, including over the head. Shivering can provide effective rewarming in cases of mild hypothermia. If victims feel comfortable exercising, that can also increase the rewarming rate. Exercise will slightly increase afterdrop — a continued decline in victims' core temperature even after their removal from the cold stress — but this is typically not problematic in cases of mild hypothermia. Fully alert and cooperative victims of hypothermia can also drink warm liquids. These deliver negligible amounts of heat but help offset associated dehydration and impart a sense of comfort. Most beverages are suitable — but avoid alcohol, as it can compromise victims' awareness and exacerbate dehydration and vasodilatation (expansion of the blood vessels). Food can improve victims' energy reserves, but it's not a critical immediate need for well-nourished victims.

Individuals with moderate hypothermia will be conscious but may be confused, apathetic, or uncooperative and may have difficulty speaking. Moderate hypothermia demands more caution, since cardiac arrhythmias (disturbances of the heart's rhythm) can be expected. Gentle handling and active rewarming techniques — such as heated blankets, forced-air rewarming, and heated and humidified breathing gas — are all desirable, if they're available. Exercise is not recommended for those with moderate hypothermia, due to its potential for increasing afterdrop and to victims' compromised physical coordination. Afterdrop can raise the risk of physiological collapse, especially during or shortly after a rescue from immersion-related hypothermia. Gentle handling, including keeping victims supine (lying on their back, face up), with their heart and head at similar levels, and completely at rest will reduce the risk of collapse. Use the most effective alternatives at hand when rewarming. Take care to insulate victims from the ground or other cold surfaces (for example, consider using a wetsuit as an insulated "mattress"). A warm-water bath is another good option for victims of moderate hypothermia — but it's essential to physically support them throughout their transfer to the bath and their immersion. The initial bathwater temperature should be lukewarm, definitely not more than 105°F (41°C), to minimize the sensation of burning that victims will likely experience. After immersion, the water temperature can be progressively increased to no more than 113°F (45°C). If hot water isn't available, moderately hypothermic individuals can be rewarmed with chemical packs or electric pads; to avoid burns, however, they should never be applied directly to the skin.

Individuals with severe hypothermia may be unconscious, may have a slowed heart rate and respiration, or may even appear dead, with no detectable heartbeat. Look very carefully for signs of life, such as breathing, movement, or a pulse in the neck (in the carotid artery). Assess their breathing first, then their pulse, for a period of at least one minute to confirm either respiratory arrest or pulseless cardiac arrest, which would necessitate cardiopulmonary resuscitation (CPR). If hypothermia is caused by cold-water immersion, death usually results from loss of consciousness and subsequent drowning. If drowning precedes hypothermia, successful resuscitation is unlikely. But if victims evidence breathing or movement, that means their heart is still beating, even if at a slow rate. Spending sufficient time to check for the existence of a pulse is essential. If there is either breathing or a heartbeat, external heart massage (also known as chest compression) is not needed. For the unconscious hypothermic individual, the main goals are to maintain adequate blood pressure and respiration and to prevent further heat loss. Severe hypothermia leaves victims susceptible to cardiac arrest, so extremely gentle handling — putting them in a supine position with their head and heart at the same level, fully supporting them, and keeping them from all physical activity — as well as aggressive, often invasive rewarming strategies are essential. Cardiac arrhythmias may result from severe hypothermia — and even from rewarming a severely hypothermic individual. Basic life support takes precedence over efforts to rewarm a victim.

If there are no signs of life in a hypothermic individual, begin CPR and make arrangements for emergency transport to the nearest medical facility. Rewarming victims of severe hypothermia is almost impossible in the field. But it is essential to protect them against further heat loss. If CPR is required, it should be continued, if possible, until medical assistance is obtained. There have been successful resuscitations after prolonged CPR, in part because of some naturally protective effects of hypothermia. In occasional cases, victims who appear clinically dead, due to marked decline in their brain and cardiovascular function, are fully resuscitated, with their neurological functions intact. Learn more about CPR from Alert Diver online . However, the outlook is poor for adults who have a core temperature below 82°F (28°C), have been immersed for more than 50 minutes, have life-threatening injuries, or are more than four hours from definitive medical care.

In hypothermic individuals, discontinue CPR only under these conditions:
* The person is successfully resuscitated.
* The rescuers become too fatigued to continue.
* The person has been completely rewarmed but is still unresponsive to properly administered CPR.
* A medically qualified individual arrives at the scene and, after examining the victim, declares the person dead.
The following steps are advised following a cold-water immersion incident:
* Determine the cause of the immersion to reduce risk to the rescuers.
* Handle the victim as gently as possible.
* Assess the victim for responsiveness and normal breathing (and be aware of the increased risk of cardiac arrest while the victim is being handled and removed from the water).
* If breathing is absent, begin CPR and continue it until medical personnel arrive.
* Give the victim as much oxygen as possible.
* Determine the cause of the immersion.
* If any injury is suspected, support and immobilize the victim's neck as well as possible.
* Arrange transport to a medical facility.
* Prevent further heat loss.
* Rewarm as needed and as the situation allows.
The protocol for aiding victims of nonimmersion-related hypothermia are the same, aside from the steps related specifically to immersion.

Prevention: Preventing hypothermia if you plan to swim or dive in cool or cold water requires preparation. It is essential that divers understand the proper use of protective garments to conserve their body heat and control heat loss. Most divers will benefit from wearing thermal protection in water cooler than 80°F (27°C). Significant thermal stress can be expected in water colder than 75°F (24°C). Divers should ensure that they have the proper protective equipment, as well as training and experience in how to dive safely in cool or cold water. Immersion in cold water without thermal protection results in incapacitation much faster than one expects. An additional aspect of preparation involves training and readiness in case a rescue (or self-rescue) is necessary; rapid action greatly increases the likelihood of a successful outcome in such an instance.

Preventing hypothermia if you plan to engage in surface or land-based activities requires wearing appropriate clothing for the conditions; dressing in layers and wearing a hat to prevent body heat from escaping from your head are especially beneficial. It is also important to stay dry and to avoid overexertion, which can cause you to sweat and get chilled if the sweat cools before it evaporates.

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