Drowning: Encyclopedia II - Drowning - The drowning process

Drowning - The drowning process

Drowning - Common situations leading to drowning

Most drownings occur in water, drownings in other fluids are comparatively rare and often industrial accidents. Surveys suggest that 90% of drownings occur in freshwater (rivers and lakes) rather than in the ocean.

Well known mechanisms by which a person drowns can be categorized as follows:

• Physically hindered in the attempt to extricate self (e.g. lack of consciousness, injury, being trapped, or hampered by clothing)
• Physiological inability to remain floating in a body of water, often due to a combination of exposure, hypothermia, shock or exhaustion. (Cold, such as ocean water, is a major contributor to these)
• Inimical action of the water itself (rip tides, currents, waves, eddies)
• Acute illness interfering with bodily motor functions (e.g. heart attack or stroke whilst swimming)
• Forcible submersion by another person (i.e. murder)

Causes underlying this may include accidents such as falling through ice, or the influence of drink or drugs, since lack of good judgement is a major enhancer of risk (PCP users frequently lose their sense of direction as well, and drowning is a major cause of death for them), and lack of skill (inability to swim, going out of one's depth). A few centimeters of water are sufficient for drowning in certain circumstances, if the victim is lying face down on the water (child in bath, alcoholic falling unconscious in puddle)

Drowning may also be due to strong negative buoyancy, where the victim is forced underwater by an object that is denser than water. Near drowning victims often report that their last thought before unconsciousness was imagining other peoples reaction to their drownings, and feeling embarrassed and ashamed for being stupid enough to drown, believing that smart people would be able to prevent their own drownings. (For a list of causes see swimming)

Drowning - Initial Reactions to Submersion

Submerging the face into water causes the mammalian diving reflex, which is found in all mammals, and especially in marine mammals such as whales and seals. This reflex puts the body into energy saving modus to maximize the time an organism can stay under water. The effect of this reflex is greater in cold water than in warm water, and includes three factors:

• Bradycardia, a reduction in the heart rate of up to 50% in humans.
• Peripheral Vasoconstriction, the restriction of the blood flow to the extremities to increase the blood and oxygen supply to the vital organs, especially the brain.
• Blood Shift, the shifting of blood to the thoracic cavity (region of the chest between the diaphragm and the neck) to avoid the collapse of the lungs under higher pressure during deeper dives.

Thus both a conscious and an unconscious person can survive longer without oxygen under water than in a comparable situation on dry land.

Drowning - Initial Oxygen Starvation

A conscious victim will hold their breath (see Apnea), and will try to access air, often resulting in panic, including rapid body movement. This uses up more oxygen in the blood stream and reduces the time to unconsciousness.

The victim can voluntarily hold their breath for some time, but the breathing reflex will increase until the victim will try to breathe, even when submerged. The breathing reflex in the human body is weakly related to the amount of oxygen in the blood but strongly related to the amount of carbon dioxide. During apnea, the oxygen in the blood is used by the cells, and converted into carbon dioxide. Thus, the level of oxygen in the blood decreases, and the level of carbon dioxide increases. Increasing carbon dioxide levels lead to a stronger and stronger breathing reflex, up to the breath-hold breakpoint, at which the victim can no longer voluntarily hold their breath. This typically occurs at an arterial partial pressure of carbon dioxide of 55mm Hg, but may differ significantly from individual to individual and can be increased through training. Decreasing oxygen levels, however, lead to a sudden loss of consciousness without warning, usually around a partial pressure of 25 to 30mm Hg. This condition of inadequate oxygen is called hypoxia. Trained apnea divers can hold their breath and resist the breathing reflex until they pass out. The loss of consciousness due to hypoxia is called shallow water blackout when it occurs as the victim is ascending from a dive; the decreasing water pressure around the victim causes the partial pressure of oxygen in the blood to also decrease. The loss of consciousness due to hypoxia is more likely when rapid breathing before apnea decreased the level of carbon dioxide in the blood without increasing the level of oxygen, as the blood is usually saturated with oxygen. Therefore, blackout may occur without warning before a breathing reflex is felt. Breath holding in water should never be preceded by rapid breathing to store oxygen, and should always be supervised by a second person.

Drowning - Water entering the upper airways

If water enters the airways of a conscious victim, the victim will try to cough up the water, or swallow it, thus inhaling more water involuntarily. Upon water entering the airways, both conscious and unconscious victims show laryngospasm, i.e. the Larynx or the vocal cords in the throat constrict and seal the air tube. This prevents water from entering the lungs. Due to this laryngospasm, water enters the stomach in the initial phase of drowning and very little water enters the lungs. Unfortunately, this can prevent air from entering the lungs too. In most victims, the laryngospasm relaxes some time after unconsciousness, and water can enter the lungs; this is called wet drowning. However, about 10-15% of victims maintain this seal until cardiac arrest; this is called dry drowning as no water enters the lungs. In forensic pathology, water in the lungs indicate that the victim was still alive during drowning. The absence of water in the lungs may be either a dry drowning or a death before submersion.

Drowning - Unconsciousness due to Oxygen Starvation

Oxygen starvation will render a victim unconscious. An unconscious victim rescued with an airway still sealed due to laryngospasm stands a good chance of experiencing no ill after effects. Also, since little water has entered the lungs, no water has to be removed before beginning artificial respiration. In most victims, the laryngospasm relaxes some time after unconsciousness, and water fills the lungs resulting in a wet drowning. Freshwater contains less salt than blood, and will therefore be absorbed by the blood stream due to osmosis. In animal experiments, this changed the blood chemistry and lead to cardiac arrest in 2-3 minutes. Salt water is much saltier than blood, and due to osmosis, water will leave the blood stream and enter the lungs. In animal experiments, the thicker blood requires more work from the heart, leading to cardiac arrest in 8 to 10 minutes. However, autopsies on human drowning victims show no indications of these effects, and there appears to be little difference between drownings in salt water and fresh water.

Drowning - Secondary drowning

Water, regardless of its salt content, will damage the inside surface of the lung, collapse the alveoli and cause a hardening of the lungs with a reduced ability to exchange air. This may cause death even hours after rescuing a conscious victim. This is called secondary drowning. Inhaling certain poisonous vapors or gases will have a similar effect.

Drowning - Cardiac Arrest and Death

Due to lack of oxygen or chemical changes in the lungs, the heart may stop beating. This cardiac arrest stops the flow of blood, and thus stops the transport of oxygen to the brain. Cardiac arrest is also known as clinical death. At this point, there is still a chance of rescue. However, the brain cannot survive long without oxygen, and the lack of oxygen in the blood combined with the cardiac arrest will lead to the deterioration of the brain cells, causing brain damage and eventually brain death. In medicine, this is considered to be the point of no return where the victim is truly dead. On surface, the brain will die after approximately 6 minutes (but see 'cold water drowning', below). After death, rigor mortis will set in and stay for about two days, depending on many factors including water temperature.

Adapted from the Wikipedia article "The drowning process", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki