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Author: Ian Rogers MMBS FACEM | Professor of Emergency Medicine, St John of God Murdoch Hospital & University of Notre Dame Fremantle
Cold water immersion is also called cold water shock.
It is a common misconception that death related to cold water immersion (eg while swimming across a mountain river, a trapped canoeist) is usually due to hypothermia. Even when immersed in very cold (<10OC) water it takes some time (more than an hour) for the body core temperature to drop substantially.
What does cool quickly are the limbs, and as they cool the nerves that send messages to the muscles to move quickly cease to function. Consequently most people who die in very cold water die from drowning as they can’t swim, and not because of core hypothermia.
Another recognised cause of death is cold water immersion syndrome where diving into very cold water stimulates a nerve that slows the heart substantially or even stops it. If the patient doesn’t drown because of loss of consciousness when the heart stops then the heart may restart itself (especially if supported by brief CPR).
Both of these cold water syndromes described above emphasise why buoyancy or flotation aids are so important to keep the head above water if cold water immersion occurs.