The Four Stages of Cold-Water Immersion

Taken from On Scene, The Journal of U.S. Coast Guard Search and Rescue, Fall 2006, pg. 13
Written by RADM Alan Steinman, USPHS (Ret) and Gordon Giesbrecht, Ph.D.


Falling into cold water can be life-threating.  There are four stages of cold-water survival, and each presents the survivor with a different challenge.  The stages are: 1) cold-shock; 2) functional disability; 3) hypothermia; and 4) post-rescue collapse.  It is important to understand the risks of each stage in order to be properly prepared to survive a cold-water emergency.

Stage 1: Cold-shock (0-2 minutes): Sudden immersion in cold water causes an immediate fall in skin temperature which triggers several body reflexes.  These reflexes are collectively known as the "cold-shock" response, and they last for just the first few minutes after falling in.  The cold-shock responses are: 1) instantaneous gasping for air; 2) sudden increase in breathing rate; 3) sudden increase in heart rate; 4) sudden increase in blood pressure; and 4) dramatic decrease in breath-holding time.  If your head is underwater and the cold-shock reflex causes you to gasp and inhale (and simultaneously decreases your ability to hold your breath), you may breathe in water and drown.  This has happened often enough in the past that the Coast Guard had a term for it: "sudden drowning syndrome."  It's one reason why a personal flotation device (PFD) can be life-saving -- it helps keep your head out of the water during the first few minutes the cold-shock reflexes are active.

The increase in blood pressure and heart rate from sudden immersion into cold water can also be fatal.  These rapid changes in the cardiovascular system can trigger irregular heart beats or even cardiac arrest in susceptible individuals.  But even aside from the potential for cardiac arrest, the irregular heart beats and rapid breathing rate can be incapacitating for someone struggling to keep his head above the waves.  This is yet another good reason why a PFD can be life-saving in this situation:  it helps you stay afloat until your heart rate, blood pressure and breathing rate return to more normal levels when the cold-shock reflexes diminish.

Sudden immersion in cold water also drastically reduces your ability to hold your breath.  For the average person who can hold his breath for 60 seconds in air, breath-holding time is reduced to 20-25 seconds or less when submerged in water colder than about 50 degrees Farenheit.  This would obviously be a problem for someone trying to escape from a submerged automobile, vessel or aircraft.  Finally, the rapid breathing that occurs during the first few minutes of cold-water immersion can lead to a drop in blood levels of carbon dioxide with subsequent mental confusion or even unconsciousness; both can significantly increase your chances of drowning, particularly if you're not wearing a PFD.

Stage 2: Functional Disability (2-30 minutes):  If you survive the cold-shock reflexes after falling overboard, cold water can still affect you in other ways.  It is much harder to swim in cold water than it is in warm water.  Your muscles get cold, making it harder to use your arms and legs to stay afloat.  And cold water is a bit more vicous than is warm water, requiring you to work harder to swim or stay afloat.  Your hands get cold quickly and you lose manual dexterity and grip strength.  This can affect your ability to grasp a rescue line or life ring or even to help pull yourself back aboard your vessel.  Both swimming failuer and loss of manual dexterity can occur during the first 30 minutes after falling into cold water.  Again, a PFD would be life-saving during this period, as it would dramatically decrease your need to swim to keep your head up.

Stage 3: Hypothermia (>30 minutes):  Hypothermia is a decrease in the body's core temperature (i.e., a drop in the temperature of the body's vital organs below 95 degrees Farenheit) resulting from excessive heat loss to the cold water.  Hypothermia is not really a threat until you have been immersed in cold water for at least 30 minutes.  The body cools relatively slowly, even in extremely cold water.  When the body's temperature falls to around 86-90 degrees Farenheit, you will lose consciousness and likely drown.  But even in ice-water, this could take an hour or more to occur.  In warmer water, the timeto unconsciousness could be much longer, depending on your body size and weight (large and/or obese people survive much longer than small, skinny people), your clothing, your state of health, the sea-state, and particularly on whether you're wearing a PFD or some other means of flotation.  But without a PFD or supplemental flotation, unconsciousness in the water usually means immediate drowning.  Survival times for the average sized person wearing an insulated worksuit with inherent buoyancy (e.g., and insulated exposure coverall and medium-weight undergarments - not a survival suit) in 45 degree Farenheit water, even in heavy seas, could be as long as 5-8 hours.  For the same person wearing a survival suit, properly donned before entering the water, the survival time could be as long as 36 hours!

Stage 4: Post-Rescue Collapse (>30 minutes):  A survivor is still at significant risk even after removal from the water.  Significant levels of hypothermia can slow the body's normal defenses against a sudden drop in blood pressure.  This can occur when the survivor is removed from the water, particularly if he/she is rescued in a vertical posture and not promptly placed in a horizontal posture in the rescue vessel or aircraft.  The hypothermic heart and arteries cannot adjust fast enough to the drop in blood pressure, which may cause loss of consciousness, irregular heart beats or even cardiac arrest.  Furthermore, the body's core temperature continues to fall even after a survivor is removed from the water, a phenomenon known as "afterdrop."  If the afterdrop lowers the heart temperature too far (e.g., below avout 77 degrees Farenheit), cardiac arrest may occur.  Finally, metabolic changes in the body caused by prolonged immersion hypothermia can contribute to potentially fatal cardiovascular effects even after a survivor is rescued.  For all of the above reasons, rescuers should be particularly mindful of the ABC's of first aid, handle a hypothermic victim gently, begin gentle rewarming efforts in the rescue vehicle, and transport the survivor to a site of definitive medical care.