You're backcountry skiing with friends when you arrive at what appears to be an open field. You're halfway there when you hear crunching under your skis. Suddenly, you fall into a frozen lake. The cold water is a shock. It feels like thousands of needles piercing your body. You gasp and start hyperventilating. You try to grab the edge of the ice, but the weight of your pack and skis makes it nearly impossible to stay afloat. You're convinced you're going to drown or die of hypothermia. What can you do?

Deaths from cold water immersion occur every year—even among swimmers trying to cool off in Lake Tremblant on a hot summer day! Most people believe hypothermia will kill them within 5 minutes of immersion, so they panic and drown. In reality, you have more than 30 minutes before you become hypothermic, even in ice water. Let's examine the different phases the body goes through during cold water immersion.

Phase 1: The Heat Shock Response

The heat shock response is the body's initial reaction to immersion in water colder than 15-20°C. Rapid cooling of the skin triggers a gasp reflex, hyperventilation, and an inability to hold one's breath. This response can cause drowning if the victim's head is submerged upon initial entry into the cold water and can contribute to drowning in conditions where the victim would be required to hold their breath (waves, surf, white water, current, open sea, etc.). Cooling of the skin also causes peripheral vasoconstriction and increases cardiac output, heart rate, and blood pressure. These sudden cardiovascular changes can cause cardiac arrhythmias, myocardial infarction, and stroke in susceptible individuals. For those who manage to relax and control their breathing, heat shock typically subsides within 1 to 2 minutes.

Phase 2: Cold Incapacitation

Survivors of the heat shock response will then experience cold incapacitation, or a loss of basic neuromuscular skills caused by cold. Cold incapacitation typically occurs during the first 10 to 15 minutes of cold water immersion. Significant peripheral cooling of muscle and nerve fibers results in stiffness of the extremities, poor coordination of gross and fine motor activity, loss of power, and an inability to swim. During this phase, it becomes increasingly difficult to perform basic lifesaving procedures, such as grasping a rescue rope. Victims of cold incapacitation drown due to an inability to swim before hypothermia has a chance to set in.

Phase 3: Onset of Hypothermia

Most cold water immersion deaths result from drowning during the first two phases of cold water immersion. Hypothermia only becomes a significant problem if immersion lasts longer than 30 to 60 minutes. Hypothermia occurs when the continued loss of body heat lowers core temperature. Hypothermia victims will eventually lose consciousness and drown unless they wear a PFD (personal flotation device) or some other factor allows them to stay afloat. If the victim's head is kept above water, they could survive for an additional hour or more before their heart stops beating.

Phase 4: Rescue Collapse

Despite recovery in an apparently stable condition, a cold water immersion survivor may experience rescue collapse, ranging from fainting to cardiac arrest, during the rescue period. Deaths due to rescue collapse have occurred from a few minutes before rescue to up to 24 hours afterward. Three causes of rescue collapse have been proposed. The first is secondary core temperature decline, where core temperature continues to decline even after cold water immersion has ended. The second is a collapse in blood pressure. When rescue is imminent, the victim may relax enough to cause a drop in blood pressure, which can, in turn, cause fainting and drowning. Rescue itself can also lower blood pressure. Removing a victim from the water in an upright position relieves hydrostatic pressure around the lower limbs and causes blood to pool in the legs, which then lowers blood pressure. It is therefore important to remove cold water immersion victims in a horizontal position. The third proposed cause of rescue collapse is related to factors that increase the risk of ventricular fibrillation, such as hypoxia, acidosis, and rapid pH changes. Additional cardiac strain or rough handling may be enough to cause cardiac arrest of the hypothermic heart. Cold water immersion victims must be handled very gently during and after rescue to avoid cardiac irritation.

So, back to our case, what can you do? Well, it's best to avoid cold water exposure altogether, but when that's not possible, you can make sure you're prepared for the possibility of cold water immersion.

Before possible exposure:

• Assess your swimming ability and practice self-rescue techniques in various cold water conditions (waves, surf, whitewater, current, open water, etc.).
  
• Wear insulating clothing, such as a drysuit or wetsuit.
  
• Wear a foam life jacket rather than an inflatable one. Without a life jacket, you'll expend precious energy staying afloat and won't be able to keep your head above water if you lose consciousness.

If you are immersed in cold water:

• Whenever possible, try to enter the water slowly and without submerging your head. Never dive into cold water.
  
• For the first minute, control your breathing and DO NOT panic. Then exit the water as soon as possible.
  
• Only begin swimming if you can reach safety in less than 30 minutes.
  If self-rescue is not possible, minimize your exposure, ensure your flotation, and call for help. Actions to minimize heat loss should be initiated.
  
• If you are alone, use the HELP position (heat loss reduction position). Remain as still as possible with your arms pressed against your chest and your legs bent and pressed together.
  
• If you are in a group, huddle together. Bring the sides of your chests together as much as possible, wrap your arms around each other's backs, and intertwine your legs.

Remember you have 1 minute-10 minutes-1 hour: 1 minute to control your breathing, 10 minutes of effective movement to get out of the water or protect yourself from drowning, and 1 hour before you lose consciousness due to hypothermia.