*This material can also be seen on the website, Scubadoc's Diving Medicine
What is hypothermia and near-drowning?
Hypothermia is a lowered body temperature less than 95 degrees F. Cold water near-drowning is considered a submersion accident often leading to unconsciousness or coma in water temperatures of 70 degrees F or less. A long submersion time is considered 4 to 6 minutes or greater. (See further discussion below)
Why is this important to scuba divers?
Decompression sickness or air embolism often lead to immersion hypothermia and cold water near-drowning as the natural consequences of these diving accidents.
How does this occur?
The body loses heat to the environment by:
- Conduction, the transfer of heat by direct contact with the water, air or ground
- Convection, the transfer of heat by air or water that moves away
- Radiation, the transfer of energy by non-particulate means, heat loss from an unprotected head
- Evaporation, conversion of water droplets (sweat) into water vapor, thereby absorbing calories of heat.
Why is hypothermia dangerous?
Hypothermia may be mild, moderate, or severe. The presentation may range from shivering and piloerection ("goosebumps"), to profound confusion, irreversible coma and death. Significant hypothermia begins at temperatures of 95 degrees F and below. The lowering of the body temperature occurs as the body is robbed of heat by the surroundings. Water conducts body heat away up to 26 times faster than air of the same temperature. Normal body functions slow down with decreasing heart rate, decreasing respiratory and metabolic rate. Thinking is impaired and speech becomes confused. Reflexes are slowed and muscles become stiff and unusable. Then dangerous life-threatening heart rhythms develop which are hard to reverse.
What is a 'diving reflex'?
On immersion in very cold water, reflex actions occur right away. There is sudden hyperventilation, an involuntary gasp, and a varying amount of diving response follows. The diving response is more evident in the very young (infants and toddlers); it consists of a slowing of the heart beat, a decrease or cessation of respiration and a dramatic change in the circulation of the blood with circulation only to the most inner core of the body, the heart, lungs and brain. The casual observer sees this victim as cold, blue and not breathing. These victims appear dead. Cold water immersion victims have been fully resuscitated when treated carefully with a variety of rewarming techniques ranging from warm blankets to complete cardiopulmonary bypass techniques in major hospitals.
Differences in cooling rates occur depending on the age of the victim, sex, body weight, protection worn, nutritional status, general health, specific diseases, water temperature, length of exposure, areas of exposed heat loss, rough versus calm seas, circumstances of the immersion and the "will to live".
*Remember: Immersion hypothermia should be considered part of most dive accidents.
The body loses its temperature in a variety of ways: in the water, after removal and during transport. Cold water immersion victims may look dead but may be entirely resuscitatable.
How can hypothermia victims be recognized?
SYMPTOMS AND SIGNS
2. LOWERED BODY TEMPERATURE
3. COLD BLUE SKIN
4. SLOW HEARTBEAT
5. SLOW RESPIRATION
6. SLURRED SPEECH
8. MUSCLE STIFFNESS
9. CARDIOPULMONARY ARREST
What can be done to assist the hypothermic victim?
The basic goals of early care are to prevent cardiopulmonary arrest, stabilize the core temperature, then carefully transport the victim to definitive medical care.
1. Removethe patient from the cold environment.
2. Check the ABC's of airway adequacy, breathing and circulation. If acceptable, then we add a "D" as in ABCD: DEGREES - what is the body temperature? A low reading thermometer is commercially available (most clinical thermometers read to 94 degrees F only) and this should be part of an emergency kit. As always, if the patient is not breathing and the heart not beating, standard cardiopulmonary resuscitation (CPR) should be started immediately.
3. Prevent further heat loss. This is done by removing wet clothing, gentle drying of the skin, remove or cut off suits, covering the high heat loss areas of the body, e.g., the head and neck (accounts for 50% of the heat loss), the lateral thorax and groin areas.
4. Gentle handling is a must. As the body rewarms it gets colder first for a short time; this is known as afterdrop.
Why is 'afterdrop' so dangerous?
During this period the heart is very vulnerable to developing life threatening rhythm disturbances. Immediately after rescue the victim should be removed horizontally from the water and kept that way. A litter or stretcher should be used to carry the victim since unnecessary exercising, jumping, climbing or exertion may trigger the heart rhythm disturbance.
Victims may deny they are ill and want to decline medical care, or want to climb into ambulances or helicopters on their own. Remember their judgement may be clouded, and yours should prevail.
Afterdrop can be worsened by certain types of "field treatments", such as a cigarette, a hot cup of coffee and a drink of alcohol, all time-honored treatments. These all prolong the afterdrop and may not help the hypothermic victim recover. They should not be given to hypothermic individuals with core temperatures below 95 degrees F.
COLD WATER NEAR-DROWNING
Are cold water near-drowning victims any different from warm water victims?
Submersion accidents which lead to unconsciousness in waters colder than 70 degrees F occur with regularity. Oxygen needs are much reduced when the body is cold, therefore a permanent brain damage from low oxygen states may not occur. A 60 minute cold water submersion victim has been fully resuscitated. Similar to the hypothermic victims above these nearly drowned individuals appear cold to touch, blue, with no respiration or evident circulation and their pupils are fixed and dilated.
What is the pathophysiology of drowning?
The principal physiologic consequence of immersion injury is prolonged low oxygen level in the blood (hypoxemia). After initial gasping, and possible aspiration, immersion stimulates hyperventilation, followed by voluntary cessation of breathing and a variable degree and duration of laryngospasm. This leads to hypoxemia. Depending upon the degree of hypoxemia and resultant acidosis, the patient may develop cardiac arrest and central nervous system (CNS) lack of blood supply (ischemia). Asphyxia leads to relaxation of the airway, which permits the lungs to fill with water in many individuals ("wet drowning"). Approximately 10-20% of individuals maintain tight laryngospasm until cardiac arrest occurs and inspiratory efforts have ceased. These victims do not aspirate any fluid ("dry drowning").
In young children suddenly immersed in cold water, the mammalian diving reflex may occur and produce apnea,
bradycardia, and vasoconstriction of nonessential vascular beds with shunting of blood to the coronary and cerebral circulation.
The target organ of submersion injury is the lung. Injury to other systems is largely secondary to hypoxia and ischemic acidosis. Fluid aspirated into the lungs produces vagally mediated pulmonary vasoconstriction and hypertension.
Freshwater moves rapidly across the alveolar-capillary membrane into the microcirculation. Surfactant destruction occurs, producing alveolar instability, atelectasis, and decreased compliance with marked ventilation/perfusion (V/Q) mismatching. As much as 75% of blood flow may circulate through hypoventilated lungs.
In salt water near drowning, surfactant washout occurs, and rapid exudation of protein-rich fluid into the alveoli and pulmonary interstitium is observed. Compliance is reduced, direct alveolar-capillary basement membrane damage is seen, and shunting occurs. This results in rapid production of serious hypoxia. Fluid-induced bronchospasm also may contribute to hypoxia.
What are some of the factors relating to surviving cold water near-drowning?
- Age of the patient - the younger the better the prognosis
- Length of submersion - the shorter the better
- Water temperature - the colder the better the survival
- CPR - if appropriately applied the better the survival
- Water Quality - the cleaner the better the survival
- Struggle - the more struggle the worse the results
- Other injuries - burn, blast, fractures reduce the survival
How can I recognize cold water near-drowning?
SIGNS and SYMPTOMS
1. COUGH, CLEAR TO FROTHY RED SPUTUM
2. BLUE SKIN COLOR
3. SHORTNESS OF BREATH
4. CONFUSION TO COMA
5. RESPIRATORY ARREST
6. CARDIAC ARREST
What is the early management of the diver with cold water near-drowning?
1. Remove from the water
2. Do not do a Heimlich Maneuver, as it may induce vomiting and aspiration.
3. ABC's of resuscitation, begin CPR if indicated.
5. Remove wet or constricting clothing, wet suits, etc.
6. Transport to the nearest medical facility, noting that if this is a diving accident a recompression chamber will be necessary. Decompression sickness or air embolism may have led to the cold water near-drowning in the first place and full resuscitation should be done inside the chamber to be successful.
Thermal Protection and Hypothermia Considerations
Adapted from Martin J. Nemiroff, M.D.
Thermal protection is paramount for undersea recreation, effective work, and military warfare needs. Heat loss is accentuated by many factors including the increased thermal conductivity of water as compared to air of the same temperature. The study of immersion hypothermia has increased survivability in downed pilots and aircrew, shipwreck victims, sport scuba enthusiasts, and near-drowned victims.
Where does the body lose heat ?
- Head, neck, axilla, and inguinal region, for the most part
- 50 % lost from the head and neck alone heat flux across the skull, blood vessels close to surface
- Remember children lose heat quicker because of ratio of body mass to skin surface
- Conduction-the transfer of heat by direct contact with water, air or ground
- Convection-the transfer of heat by air or water that moves away
- Radiation-the transfer of energy by non-particulate means, heat loss from an unprotected head
- Evaporation conversion of water droplets (sweat) Into water vapor, thereby absorbing calories of heat
- Create a micro-climate around body with insulators
- Waders, gloves, hats, boots, shoes
- Wet suits made of closed cell neoprene
- Dry Suits and under garments
- Clothing In layers, virtues are loose fitting, air trapping, no ligatures, belts, zippers
- Head coverings
- Water Temperature
- Outside Air Temperature (OAT)
- Wind, wind-chill
- Wave action, sea state
- Wet clothes versus dry (5 times greater loss)
- Body habitus
- Sexual differences
- Air versus water (water 25 times greater loss)
- Breathing Gas, air helium
- Activity level, breathing rate
- Fear, panic
- Fight or flight
- Beta blockers
- Effect of alcohol
- Metabolic states, thyroid function, or other medications
- Nutritional state
- Adaptation, "Polar Bear Clubs"
- Ability to shiver
- University of Victoria "U-VIC" physical education majors; Determinants of effective working suits,
- U S Coast Guard Cape Disappointment and Cape May, New Jersey Studies; Special considerations for survival suits, flying suits
- JAMA October 10, 1990 Vol 264, No. 14, Hyperkalemia a Prognostic Factor During Acute Severe Hypothermia
- JAMA ibid above. Editorial Some People Are Dead When They Are Cold And Dead.
*Adapted from M.J. Nemiroff, M.D.
Antarctica Marine ResearchLinks
Ice Rescue Training
SARBC - Hypothermial
Survival in Cold Water; Minnesota Sea Grant