A R T I C L E S

Cold Shock
by Jerry Freeman

!!Gasp!!
Sudden immersion in cold water results in an involuntary gasp (that means you can not stop it, and yes, that means all of us), followed by 1 - 3 minutes of involuntary hyperventilation. Specific data are: 2.0 litre gasp in 28o C water and 3.0 litre gasp in 10o C water (i.e. nearly your entire lung volume), and in 10o water a 600 - 1,000 percent increase in ventilation (air in and out) in the first minute. This hyperventilation results in a profound lowering of blood carbon dioxide levels and raising of blood pH levels, which causes a large risk of ventricular fibrillation (“cardiac arrest”), muscular tetany (cramps), and cerebral vasoconstriction which starves the brain of oxygen, causing disorientation and confusion.

These effects, coupled with changes in lung mechanics caused by the pressure of water on the abdomen and chest result in subjective feelings of inability to breathe and panic typically lasting 1 - 3 minutes. Most importantly for survival is a sharp reduction of maximal breath holding upon immersion. It is easy to see how these effects of gasp, hyperventilation, and impaired breath holding would result in prompt catastrophe upon a fall into cold choppy water.

Cold shock
Cold shock occurs when rapid cooling of the skin triggers a cluster of heart and breathing responses. The cardiac responses include an increase in heart rate of 40 -50%, and an increase in cardiac output of 60 - 100%, which combined with vasoconstriction of the extremities results in an average blood pressure increase to 175/93. Although a substantial strain on the heart, these changes are not likely to be a problem for a healthy, fit person but may be dangerous for those with underlying heart disease or hypertension (there have been cases of apparently near instant cardiac arrest on cold water immersion).

How cold is cold water?
Not, apparently, all that cold. The maximal hyperventilation response is reached at 10o, and near maximal gasp was reached at 11o. These are typical early spring temperatures in the English Channel.

What about hypothermia?
The vast majority of deaths in cold water occur well before body core temperature has fallen to the point of being dangerous. Even an unclothed person in 2o water will maintain core temperature for at least 20-30 minutes. Those fortunate to have survived the initial cold shock find the cold water renders the extremities neuromuscularly dysfunctional within several minutes, making self-saving operations impossible and causing death by drowning.

Recognize and manage hypothermia early - thought processes become quickly impaired and can rapidly lead to decision making which turns an unpleasant situation into a dangerous one. In a non-immersion situation, the greatest heat loss is through the head and neck, insulation for these areas is most important. In maintaining extremity function good head protection has been shown to be more useful than better gloves or socks. Get out of the water! Water will cool 20 - 30 times faster than air. Movement in the water, such as swimming, will make this even worse. Severe hypothermia is a medical crisis. The victim must be handled gently and knowledgably. “No previously healthy person should die of hypothermia after he has been rescued and treatment has been started.”

Jerry Freeman