The definition of cold water is variable but when the outside temperture is high, the water temperture only needs to be 15"c to trigger Cold Water Shock.

How our body responses to Cold-Water Immersion

Sudden immersion in cold water results in an immediate decline in skin temperature which, in turn, initiates shivering, this increases in metabolism (VO2), ventilation (VE), heart rate (HR), cardiac output (CO), and the pressure in the arteries known as (MAP). As body temperature declines and shivering ceases, VO2, HR, MAP and CO decrease proportionally with the fall in core temperature. Kidney function and extravascular fluid shifts can lead to a considerable loss of intravascular volume (amount of fluid surrounding bodies tissue), decreasing systemic perfusion (the ability to pass through cells into the tissue around).

The body's responses to cold-water immersion can be divided into three phases:

1) initial immersion and the cold-shock response;

2) short-term immersion and loss of performance; and

3) long-term immersion and the onset of hypothermia. Each phase is accompanied by specific survival hazards for the immersion victim. Deaths have occurred in all three phases of the immersion response.

We are focusing on the Initial Immersion and the Cold Shock Response:

The cold shock response occurs within the first 1-4 minutes of cold water immersion and is dependent on the extent and rate of skin cooling. The warmer the skin was initally, such as in a heat wave the more significant the differences. The responses are generally those affecting the respiratory system and those affecting the heart and the body's metabolism.

Rapid skin cooling initiates an immediate gasp response, the inability to breath-hold, and hyperventilation. The gasp response may cause drowning if the head is submersed during the initial entry into cold water. The inability to breath-hold will drown the person. Finally, hyperventilation causes arterial hypocapnia (decreased carbon dixoxide in the blood), which leads to decreased brain blood flow and oxygen supply. This may lead to disorientation and loss of consciousness.

Skin cooling also initiates peripheral vasoconstriction (outside blood vessels restrict in size) as well as increased cardiac output, heart rate and arterial blood pressure. The increased workload on the heart may lead to myocardial ischemia (heart changes) and arrhythmias, including Ventricular Fibrillation (VF). VF is the most common cause of Cardic Arrest. Sudden death can occur either immediately or within a matter of minutes after immersion.

The rate of body core cooling during cold-water immersion depends on the following variables:

1. Water temperature
2. Clothing
3. Persons Body - size etc
4. Amount of the body immersed in water
5. Behavior (e.g. excessive movement) 
6. Shivering thermogenesis

How to have some chance of surviving cold water immersion?

Cold water survival depends on avoidance of drowning and hypothermia and on the many factors related to these risks.

1. Ability to swim
2. Ability to keep the head out of water (even without flotation aids)
3. Ability to avoid panic
4. Availability and type of personal flotation device (PFD)
5. Availability of other floating objects to increase buoyancy (such as a capsized boat)
6. Water temperature
7. Physical characteristics of the survivor
8. Type of protective clothing worn against immersion hypothermia and initial immersion cold shock
9. Behavior of the survivor in the water
10. Availability of signaling devices (whistles, flares, strobe lights, radios, and mirrors) and the ability to use these devices
11. Proximity of rescue personnel

Drowning is the most immediate survival problem following water entry.  Preventing the head from entering the water may help with the initial stages of the cold water shock.

Rescue and Management of Someone in Cold Water

The main goals in prehospital management of victims of accidental immersion hypothermia are

• prevention of cardiac arrest,
• prevention of continued core temperature decline and
• moderate core (centre of the body) rewarming if possible.

Aggressive rewarming at the time of the emergency is not recommended, since the means to either diagnose or manage the many potential complications of severe hypothermia are unavailable. 

Retrieval of a victim from cold water immersion must be performed with caution. Sudden reduction of the "hydrostatic squeeze" applied to tissues below the water's surface may make high blood pressure increase. Since a hypothermic patient's normal cardiovascular defenses are impaired, the cold myocardium (muscle of the heart) may be incapable of increasing cardiac output and may cause cardiac arrest if removed from the water.

A victim's vertical posture may also cause complications to the blood pressure. The result of sudden removal of a hypothermic patient from the water is abrupt hypotension. Accordingly, rescuers should attempt to maintain hypothermic patients in a horizontal position during retrieval from the water and aboard the rescue vehicle. 

The patient's core temperature may continue to decline even after he or she has been rescued, because of the physiologic processes described earlier for "afterdrop." To reduce this the patient's physical activity must be minimized. Conscious patients should not be required to assist in their own rescue (for example, by climbing up a scramble net or ship's ladder) or to ambulate once out of the water (as by walking to a waiting ambulance or helicopter). Physical activity increases afterdrop, presumably by increasing perfusion of cold muscle tissue with relatively warm blood. As this blood is cooled, venous return (the circulatory component to afterdrop) contributes to a decline in heart temperature, increasing the risk of ventricular fibrillation VF and cardiac arrest. 

The greatest way to survive cold water shock is to think about the water you are entering and the temperature. For example Brighton Beach- sea temperatures peak in the range 18 to 21°C (64 to 70°F) on around the 1st of March and are at their coldest on about the 2nd of September, in the range 13 to 15°C (55 to 59°F). If you are feeling the effects of the heat wave, try cooling down in a slower and a kinder way to your body, spounging, fans and drinking cool water is a great way to cool off. 

Cold Water Managment is a subject on our Remote Outdoor First Aid Training Course. Next course details here