glacier and cold waterby James Hubbard, M.D., M.P.H.

Real case. A doctor falls through an ice hole while cross-country skiing. They find her body many yards away. It’s been under the ice for over an hour. She is resuscitated. After the ICU, she spends many months in rehab, but in a year she’s back to practicing medicine.

A snowmobile accident submerges a man in icy water for an hour. He lives, with no apparent brain damage.

It’s rare, but it happens. In normal circumstances the brain can’t go without new oxygen for over six minutes without developing significant damage. How can some people survive an hour of total submersion–seemingly drowned in cold water?

Part of the answer is that the rapid cooling can trigger the mammalian dive reflex.


What Causes Rapid Body Cooling?

Water conducts heat away from the body more than twenty-five times faster than just cold air. Rapid cooling is essential to trigger the dive reflex, so some of the things that put you in danger of cold-air hypothermia actually help you in this situation.

Such as being a child. Infants and babies have a higher skin-surface to body-mass ratio. Their core body temperature cools more rapidly. Older people also cool rapidly, but, sadly, other mechanisms in play make their chances not nearly so good.

Another possible cause of rapid cooling is getting a lot of cold water in the lungs. The lungs have a massive surface area. Due to a spasm of the upper airway, most people who drown don’t have a great deal of water in their lungs. The ones who do may be helped in this topsy-turvy world of cold-water drowning.


What Is the Dive Reflex?

In the dive reflex, also called the mammalian dive reflex, the rapid body cooling triggers our surface blood vessels to constrict, which shunts more oxygen-supplying blood to our inner organs and brain. The cooling also slows down our heart rate and metabolism, which decreases our body’s need for the oxygen.


The Metabolic Icebox

If your brain cools quickly, it gets even more damage protection than can be explained by the dive reflex. The protection involves dopamine release and calcium transfer and many other complicated mechanisms, but suffice it to say that neurosurgeons trigger this effect on purpose by cooling the nervous system in some brain and spinal cord surgeries.


How Does
All This Make a Difference in Resuscitation?

  1. You should still call the ambulance ASAP.
    As much as or more than ever, the best chance for recovery involves getting quick expert help. 
  2. Because of blood-vessel constriction, it may be hard to feel a pulse.
    Check for a pulse for a good sixty seconds. Look for signs of life such as breathing or slight movement. The person’s skin may be cold and blue. Their eyes may be fixated and dilated. In other words, they may look dead, but the heart could be beating. Starting CPR in a hypothermic person with a heartbeat could trigger a deadly rhythm.
  3. If you start CPR, continue it for sixty minutes.
    After checking for the sixty seconds, start CPR (the old-fashioned kind, meaning with respirations, not just chest compressions). Always consider your own safety and fatigue factor, especially if you’re all alone.

The cold fact (sorry) is the odds for survival aren’t good no matter what. If you don’t have quick access to oxygen, defibrillators, and proper warming (from expert care and in a facility) the odds are slim indeed.

Please consider taking a first-aid or CPR class. You can find one through your local hospital, Red Cross chapter, or Heart Association chapter. Ask your employer about sponsoring an on-site group class.

Note: Some CPR information in this post was updated on 6/18/14 and 6/20/14.