Sudden and prolonged cold water immersion situations correspond with distinguished physiological stages. Death may occur from one of the four stages of immersion (5):
- Stage 1 (the first 3 minutes)
à initial immersion responses (cold shock).
- Stage 2 (the first half hour)
à short-term immersion (swimming failure).
- Stage 3 (over 30 minutes)
à long-term immersion (hypothermia).
- Stage 4 (termination of immersion)
àrescue-operations (post-rescue collapse).
Cold shock and swimming failure is the leading cause of death during immersion especially in accidental situations without donned and appropriate sea-survival equipment. The severity is direct proportional to the cold water temperature.
Stage 1 – Cold Shock
The initial immersion response is a large inspiratory gasp followed by a period of severe hyperventilation. The magnitude of this reaction is directly proportional to the water temperature. By planned exposition in cold water most people will get used to it. Experience is diminishing the initial response and increasing the breath holding ability in the cold. However, lacking breath holding ability on its own can result in drowning when, even partially, submerged. Increased involuntary pulmonary ventilation goes along with massive increase of heart rate and blood pressure. Triggered by massive output of stress hormones supra-ventricular but also ventricular ectopic arrhythmias are likely to occur. If the face is submerged or even sprayed by waves frequency of arrhythmia is higher. These cardiac responses may cause death as well.
Death from cold shock by drowning or heart failure in the first three minutes of ship abandonment is common (6).
Stage 2 – Swimming Failure
The period between three and thirty minutes after immersion is characterized by cooling down of the bodies’ periphery whilst maintaining the core temperature almost unaffected.
Early swimming failure is related to ineffective swimming due to a mismatch between severe hyperventilation and swimming strokes. This increases the risk of water aspiration and drowning (6).
Delayed swimming failure is the result of muscle paralysis. During cooling down the contractility of the peripheral muscles of the upper and lower extremities will diminish linearly. Below 30°C tissue temperature in extremities peripheral blood flow falls, oxygen delivery terminates and muscles become stiff. In this situation coordinated swim strokes become impossible. Without a flotation device, or a incorrectly donned lifejacket has been, death by drowning cannot be prevented.
Swimming failure is the reason why standards for correctly wearing lifejackets must not be neglected when operating in cold water seas (7).
Another problem that develops during the first 10 – 15 minutes is diminishing manual dexterity. With cold limbs, especially impaired grip strength of the hands, it becomes impossible to carry our any self-rescue procedures, like activation or use of rescue gear or even climbing into a life-raft (7).
A muscle temperature of 28°C in the limbs will result in near total loss of strength due to impaired contractility.
Stage 3 - Long Term Immersion
Conductivity of water is 25 times that of air. After half an hour of immersion hypothermia of the body core is starting to develop steadily. An interim phase of heavy shivering that terminates at about 33°C leads to metabolic heat production. With termination of shivering the body will loose temperature continuously. However, a number of environmental, individual and intra-individual factors is affecting the rate of developing hypothermia:
- Temperature differential.
- Waves, spray, wind-chill factor.
- Insulation of clothing.
- Ability of heat production by shivering.
- Ratio of body mass to surface area.
- Mental state and coping strategies.
- Physical fitness and compromising health problems.
- Subcutaneous fat layer.
- Posture in water.
As the body temperature falls down to 30°C the hypothermic patient becomes increasingly impaired, incapacitated and falls into unconsciousness. By far the biggest threat at this incapacitation stage is drowning. Cardiac arrest is the second, and is likely to occur around 25°C.
However, the lowest recorded survival temperature without major long term sequels after accidental hypothermia in an adult person is 13,7°C (6).
Survival prediction is tricky. Over the decades numerous references have included a range of predicted survival curves. Our current knowledge indicates that death by solely due to cold develops much as reported in these references. The crucial point is whether or not the person is wearing a lifejacket that is keeping the breathing orifices at safe levels under severely impaired or unconscious conditions. The main cause of death after abandoning ship is drowning, not hypothermia. Rescue-operations are often long-lasting, and the survival time can be 24 hours or more under perfect conditions with good lifejacket, spray-hood and survival suit even in very cold water (8).
See also ch. 17
Stage 4 – Rescue-Operation and Initial Management
Just before, during or immediately following removal from the water the rescue process has its particular risks.
At the time of rescue the immersed person is likely to be suffering from one or more of the following threatening conditions:
- Blood volume alterations.
- Cardio-vascular function impairments.
- Other trauma.
Physiological changes under head-out immersion are primarily the result of a reduction of the influence of gravity, together with the hydrostatic pressure. The most important of these changes are those that influence the cardiovascular system and blood volume: enhancement of diastolic filling, cardiac output and venous return, immersion diuresis by central blood pooling and cold-induced diuresis. General cooling of the body induces relative hypovolemia though fluid shifts into the tissues.
“Post rescue collapse” is a physiological effect of removal from the water, it is a consequence of postural hypotension. Following a prolonged period of immersion, the hydrostatic assistance to circulatory function suddenly vanishes just as the full effect of gravity re-imposes itself on the body. The circulatory system now becomes functionally hypovolemic. In a vertical posture gravity tends to induce a redistribution of blood, with venous pooling in the lower limbs. The resulting reduction in blood returning to the heart will affect cardiac output and, if not corrected, the person will faint as the blood supply to the brain falls. The countermeasure of the baroreceptor reflex is impaired by the cooling and physiological vasoconstriction fails occur.
Transition from water to air during rescue from water at any temperature is likely to be less traumatic if subjects are lifted horizontally.
Survivors whose airways are not under threat of aspiration should be rescued with care, preferably horizontally, and handled as if they were critically ill, however survivors still in the water and whose airways are under threat of aspiration of water should be rescued as quickly as possible by whatever means are available (6,9).
Onboard the rescue craft, the rescued person should be placed in the optimum position to offset any potential problem in maintaining blood pressure. In a fast rescue craft, it is desirable to lay the casualty in a feet-forward, head-aft attitude. The major aim of immediate management at the rescue site is to ensure that the airway is clear and assisted ventilation is provided if required.
Because the most important cause of post-immersion death is hypoxia secondary to the aspiration of water and vomit, near-drowning victims should receive oxygen as soon as a clear airway has been established. All near-drowning and/or accidental hypothermic survivors should receive medical attention as soon as possible.
Cold survivors must be protected from further heat loss, in particular evaporative heat loss and heat loss through forced convection. Re-warming regimes must start as soon as possible.
Drowning while floating
Investigations of immersion accidents within the accepted “safe” boundaries of survival in cold waters have shown that hypothermia is not the main cause. Impairment of physical abilities and mental deterioration under moderate hypothermia, aggravated by swimming failure and the lack of a proper spray-hood, may lead to delayed drowning death despite wearing a lifejacket. Significant gastro-intestinal ingestion of sea-water and subsequently repetitive vomiting is frequent. Aspiration of vomit enhances drowning-related lung lesions, making the clinical situation worse (6).
As the majority of fatalities under immersion occur in the stages 1 and 2 before severe hypothermia has had time to develop, sea-survival equipment must focus on the short term incapacitating effects and on protection from drowning.
This underlines the absolute requirement to don sea-survival equipment as soon as possible in an emergency situation.
Sudden immersion in cold water may be life-threatening; even if it is relative cold water at about 15°C.
The “Afterdrop” Phenomenon
The so-called “afterdrop” refers to a further drop of core temperature following rescue.
There is no good evidence about its importance. The phenomenon can be neglected provided the hypothermic person is adequately rescued and re-warmed. A sudden and dramatic alteration following rescue deserves attention other than “afterdrop”. It is most likely related to post-rescue collapse, cardiac problems, internal haemorrhage or re-warming collapse due to excessively rapid re-warming (10).
Unless immediate electrolyte and blood gas measurements are available, great caution should be shown in trying to re-warm patients rapidly. Major changes are likely to have occurred during immersion. Re-warming should only ever be attempted with persons lying down at rest. Allowing hypothermic patients to stand, sit, or exert themselves makes them liable to post-rescue collapse. Excessive heating of the skin can cause re-warming collapse.
Fully Conscious and Stable Survivors
Survivors who are cold, shivering, but otherwise well and conscious can be re-warmed by immersing the torso and limbs in a bath at 37-40°C. Continuous supervision is mandatory. Water temperature must be measured using an accurate thermometer, and maintained carefully during re-warming. Once rectal temperature has reached about 36.5°C, and before they start to feel hot or start to sweat, they should carefully get out of the bath. Erect posture may again cause circulatory collapse with syncope, due to peripheral vasodilation. Drinking of hot, sweet fluids may be helpful (11).
Without any dedicated material for active re-warming most hypothermic patients should be slowly passively re-warmed in a warm, but not hot, room with frequent monitoring of vital signs: heart rate, ECG, blood pressure, and rectal temperature.
Full life support and symptomatic management should be continued until they can be carefully evacuated. If there remain no signs of life in spite of sustained and prolonged efforts to re-warm, and the patient cannot be taken to a hospital, death can reluctantly be assumed.
Forced air re-warming by appropriate air heating systems have proven to offer an extremely efficient and safe re-warming method, especially in situations without good clinical possibilities (11,12).