The Physiologic Effects of Cold Water Immersion
David W. Clauss, M.D.,
University of Vermont College of Medicine
Sudden, unexpected immersion in cold water is a risk associated with recreational activities carried out on natural ice, and brings with it a number of physiologic responses which may hinder self-rescue activities or lead directly to injury or death. This section will review the body's response to cold water immersion, with particular attention to the effects of cold exposure on the ability to carry out self-rescue on the ice.
The initial response to cold water immersion which is most evident is that of the respiratory system. Sudden immersion results in an initial gasp reflex, with involuntary inhalation and gasping, and where the subject feels as if he is unable to control his breathing. This is followed immediately by an intense stimulation of respiratory drive with resultant hyperventilation lasting several minutes. Finally, cold water immersion results in a significant decrease in breath-holding duration.
These respiratory responses have significant practical implications. The gasp reflex may result in aspiration of cold water, or may cause the subject to panic, thereby decreasing the effectiveness of self-rescue efforts. The hyperventilation may result in rapid decrease in arterial carbon dioxide, which can then lead to confusion and/or severe muscle spasms. Impaired breath-holding may have life-threatening consequences for the victim of sudden, unexpected cold water immersion.
Cold water immersion results in a number of important reflex responses in the cardiovascular system. Stimulation of cold receptors in the skin, through rapid sympathetic discharge, leads to intense peripheral vasoconstriction, with resultant reduction in blood flow to the skin and skeletal muscle. This creates a situation where the relatively warm central “core” of the trunk is surrounded by a colder “shell” of muscle and skin. This adaptive response may result in heat preservation in central organs, thereby providing a survival advantage in many situations.
However, in cold water immersion situations where survival depends on active participation by the immersed subject, this shift of blood flow away from the extremities comes at a great cost. Rapid heat loss in the limbs results in a correspondingly rapid loss of muscle strength, coordination, and fine motor abilities. The ability to perform self-rescue activities deteriorates within minutes after cold water immersion, even in the absence of an appreciable drop in core temperature. For this reason, self-rescue maneuvers must be designed to take full advantage of the brief period of intact muscular function after unexpected immersion.
The sudden sympathetic discharge associated with cold water immersion also has significant effects on heart rate and blood pressure. Heart rate rises rapidly for the first few minutes of cold exposure, and may result in myocardial ischemia or infarction (heart attack) in subjects with underlying coronary artery disease. In addition, the shunting of blood away from the cold extremities and into the truncal core results in significant increases in blood pressure, which further stresses the heart. Finally, the intense sympathetic stimulation may cause a variety of abnormal heart rhythms, and this has been proposed as the causal factor in rare cases of sudden cardiac arrest upon cold water immersion.
The shift of blood flow away from the extremities and toward internal organs results in a significant increase in urine production with possible resultant dehydration. Therefore, an important component of care after cold water immersion is aggressive rehydration.
The central nervous system is affected by cold water immersion in a number of ways. As discussed above, the initial cold shock and resultant hyperventilation can lead to a profound sense of panic, which may compromise self-rescue efforts. As core body temperature decreases, there is progressive generalized depression of brain function. This is characterized by impaired judgment, mood changes, confusion, disorientation, slurred speech, and progressive impairment of coordination.
The rapid heat loss seen after cold water immersion is a result of the remarkably high rate of heat transfer from skin to water, at least 100 times greater than occurs in air of the same temperature. The body's initial response is characterized by rapid cooling of the skin and extremities, with shunting of blood flow to the trunk and internal organs. During this time, core body temperature does not decrease, but temperature drops in the outer “shell” or extremities resulted in rapid decrease in motor function. Within 15 minutes, core temperature begins to decline as well. The rate of change in core temperature is dependent upon the balance between heat loss to the water, and heat production by the body. Heat production is maintained primarily by shivering.
A number of factors have been identified which influence the rate of cooling after immersion in cold water. The most consistent factor which protects against heat loss is subcutaneous body fat, through its effect on tissue insulation. Aerobic fitness may play a small roll in protecting against heat loss, but this is usually outweighed by the fact that highly fit people usually have less body fat. It is worth noting that ingestion of alcohol increases the rate of cooling through several effects. Perception of cold is diminished, and cold-induced impairment in judgment may be accentuated by the presents of alcohol. In addition, the shivering response, and therefore the most effective means of heat production, is diminished in the presence of alcohol. Finally, behavior can have a significant effect on the rate of cooling after cold water immersion. Vigorous exercise in cold water actually increases the rate of heat loss compared to holding still. This is because of vigorous activity results in increased blood flow to the extremities, thus decreasing the protective effect of the warm core being surrounded by the cooler shell. In addition, intense physical activity in the water increases cooling by causing an increased amount of cold water to flow beneath clothing. Therefore, if a subject is unable to remove himself from the cold water, then he can best preserve core body temperature by holding still. In addition, a position which maximizes skin-to-skin contact, such as a fetal position, will preserve core temperature more effectively than other positions which maximize skin-to-water contact.
Afterdrop is the term use to describe continued decreasing of core body temperature after someone has been removed from cold stress. As described above, the body's physiologic response to cold water immersion is to preserve central core warmth by restricting blood flow to the extremities and “outer shell” of the body. After removal from the cold water, and particularly if aggressive external warming measures are applied to the outer body surface, the warm blood from the body core is redirected back to the much colder extremities, thus cooling this blood significantly before it returns to the body core. This results in a drop in core temperature after active re-warming has been initiated. This drop in core temperature may be accompanied by adverse effects on the central nervous system, including confusion or poor decision-making, as well as by adverse effects on the cardiovascular system, including abnormal heart rhythms. For this reason, anyone who has experienced cold water immersion should be accompanied and carefully observed during the re-warming phase, and should not be responsible for activities such as driving a motor vehicle until fully re-warmed and stable.
In summary, cold water immersion results in a complex mix of physiologic changes which may compromise the ability of the immersed victim to perform self rescue. Immediate effects on respiratory drive can cause aspiration of cold water, may induce a sense of panic, or may need to hyperventilation with resultant confusion. Within minutes, coordination and muscular function in the extremities is compromised. Heart rate and blood pressure immediately rise, causing significant stress and increased work load to the heart. In addition, reflex response to immediate cold water immersion can result in abnormal heart rhythms, including possible cardiac arrest. Body heat is lost rapidly, and this may lead to central nervous system dysfunction, with resultant confusion and loss of decision-making ability.
Safe enjoyment of activities on natural ice requires the inclusion of a number of measures designed to minimize the possibility of injury or death related to cold water immersion. Primary prevention consists of the avoidance of unsafe ice conditions, as well as the use of ice poles and other measures to frequently monitor ice thickness. Secondary prevention measures are designed to minimize the chance that unexpected immersion will result in hypothermic injury. A number of safety measures can be utilized to accomplish this. Drysuits or wetsuits may be worn to minimize heat loss in the event of immersion. Ice picks should always be worn, and training and practice in their use to accomplish self-rescue is important. The same fall that can result in cold water immersion, may present a risk of head injury on the ice, and helmet use can minimize the chance of this compromising self-rescue efforts. The use of a buoyant backpack or other flotation device is important as well. It is important to travel on ice in groups, the equipped with rescue lines and well-acquainted with their appropriate use. Tertiary prevention includes taking measures to know how to contact the appropriate rescue services or access emergency care in the event of an ice emergency. With appropriate attention paid to these and other measures, recreational activities on natural ice can be enjoyed safely
Dr David Clauss, an emergency room physician in Burlington Vermont. In January 2011, he wrote this overview of what happens to the body when you fall through the ice.