Cold Water Immersion

February 1, 2019
By Jessica Duke, MD

You are backcountry skiing with friends when you come to what appears to be an open field. You get about halfway across when you hear cracking underneath your skis. Suddenly, you drop into a frozen lake. The cold water is shocking. It feels like a thousand needles stabbing every inch of your body. You gasp for air and start to hyperventilate. You grab for the edge of the ice, but the weight of your pack and skis is making it nearly impossible to stay afloat. You are convinced that you are going to drown or die from hypothermia. What can you possibly do?


Fatalities from cold-water immersion occur every year – even in swimmers looking to cool off in Lake Tahoe during a hot summer day! Most people believe that hypothermia is going to kill them within 5 minutes of immersion and so they panic and drown. In reality, you have more than 30 minutes before becoming hypothermic, even in freezing water. Let’s take a look at the different stages the body goes through when immersed in cold water.


Phase 1: The Cold Shock Response

The cold shock response is the body’s initial reaction to immersion in water colder than 15-20°C. Rapid skin cooling initiates a gasp reflex, hyperventilation, and an inability to hold one’s breath. This response can cause drowning if the victim’s head is submerged during the initial entry into cold water and can potentiate drowning in conditions where the victim would need to hold their breath (waves, surf, whitewater, current, high seas, etc.). Skin cooling also leads to peripheral vasoconstriction and increases cardiac output, heart rate, and blood pressure. These abrupt cardiovascular changes can produce cardiac dysrhythmias, myocardial infarction, and stroke in susceptible individuals. For those people who are able to relax and get their breathing under control, cold shock usually subsides within 1 to 2 minutes.


Phase 2: Cold Incapacitation

Survivors of the cold shock response will next experience cold incapacitation or loss of basic neuromuscular skills from the cold. Cold incapacitation usually occurs during the first 10 to 15 minutes of cold-water immersion. Significant peripheral cooling of muscle and nerve fibers leads to extremity stiffness, poor coordination of gross and fine motor activity, loss of power, and swim failure. During this stage, it becomes more and more difficult to execute basic survival procedures, such as grasping a rescue line. Victims of cold incapacitation drown from swim failure even before hypothermia has had the chance to set in.


Phase 3: Onset of Hypothermia

Most cold-water immersion deaths are the result of drowning during the first two stages of cold-water immersion. Hypothermia only becomes a significant problem if immersion lasts more than 30 to 60 minutes. Hypothermia occurs as continuous heat loss from the body decreases core temperature. Victims of hypothermia will eventually lose consciousness and drown, unless they are wearing a PFD or some other factor allows them to stay afloat. If the victim’s head is kept above water, they could survive for another hour or more before their heart stops beating.


Phase 4: Circum-Rescue Collapse

Despite being recovered in an apparently stable condition, a survivor of cold-water immersion can suffer from circum-rescue collapse ranging from fainting to cardiac arrest during the rescue period. Deaths from circum-rescue collapse have occurred within minutes before rescue to 24 hours after rescue. Three causes of circum-rescue collapse have been proposed. The first is core temperature afterdrop, where core temperature continues to drop even after the cold-water immersion has ended. The second is collapse of arterial pressure. When rescue is imminent, the victim may relax enough to cause a drop in blood pressure, which in turn can cause fainting and drowning. The rescue itself may also drop arterial pressure. Pulling a victim out of the water in a vertical position removes hydrostatic squeeze around the lower extremities and causes blood pooling in the legs, which subsequently decreases blood pressure. Thus, it is important to remove victims of cold-water immersion from the water in a horizontal position. The third proposed cause of circum-rescue collapse is factors that increase the risk of vfib, such as hypoxia, acidosis, and rapid changes in pH. Extra cardiac work or rough handling may be enough to induce cardiac arrest of the hypothermic heart. Victims of cold-water immersion must be handled very gently during and after rescue to avoid cardiac irritation.


So, getting back to our case, what can you possibility do? Well, it is best to avoid cold-water exposure completely, but when this is not feasible you can make sure you are prepared for the possibility of cold-water immersion.


Before possible exposure:

  • Assess your swimming ability and practice self-rescue skills in different cold-water conditions (waves, surf, whitewater, current, high seas, etc.).
  • Wear insulated clothing, such as a drysuit or wetsuit.
  • Wear a foam, rather than inflatable, life jacket. Without a life jacket, you’ll expend valuable energy treading water and will be unable to maintain your head above water in the case you become unconscious.


If you are immersed in cold water:

  • When possible, try to enter the water slowly and without submersing your head. Never dive into cold water.
  • In the first minute, get control of your breathing and DON’T panic. Then get out of the water as soon as possible.
  • Start swimming only if you will be able to reach safety within 30 minutes.
  • If self-rescue is not possible, minimize your exposure, ensure flotation, and call for assistance. Actions to minimize heat loss should be initiated.
    • If you are alone, use the HELP or heat escape lessening position. Remain as still as possible with your arms pressed against your chest and your legs flexed and pressed together.
    • If you are with a group, huddle together. Get the sides of everyone’s chests as close together as possible, wrap your arms around each other’s backs, and intertwine your legs.


Remember that you have 1 minute-10 minutes-1 hour: 1 minute to get your breathing under control, 10 minutes of meaningful movement to get out of the water or to secure yourself against drowning, and 1 hour until you become unconscious from hypothermia.