Science Fair Project Encyclopedia
Drowning is death due to asphyxia caused by immersion in fluid, usually water. Near drowning is initial survival of a drowning accident which can lead to serious secondary complications including death; cases of near drowning therefore require attention by medical professionals. Secondary drowning is death due to chemical and biological changes in the lungs after a near drowning incident or exposure to chemicals. In many countries, drowning is one of the leading causes of death for children under 14 years old.
2.1 Situations leading to drowning
About 6500 drowning deaths occur in the United States every year, and an estimated 140,000 worldwide. No one is certain about the rate of near drowning incidents. Most of the victims are either young children, especially boys, or young adolescent males. In some regions, drowning follows car accidents as the second most likely cause of injury and death for children. Surveys indicate that 10% of the children under 5 experienced a situation with a high risk of drowning. Males, in general, are much more likely to drown than females. Also, 90% of drownings occur in freshwater. Drowning related injuries are the fifth most likely cause of accidental death in the US. The drowning cases in the US are as follows:
- 3100 drownings related to swimming
- 1200 Boating related drownings
- 700 Scuba diving related drownings
- 500 Motor vehicle related drownings
- 1000 drownings of undetermined origin
The drowning process
Situations leading to drowning
Drowning is caused by immersion in fluid. This requires the victim to be immersed in fluid and to be unable or unwilling to rescue him or herself. Most drownings occur when the victim is unconscious or exhausted and unable to access air. This may be, for example, a swimmer who experiences a heart attack while in the ocean, exhaustion and coma due to hypothermia after breaking through the surface of a frozen lake, or merely a drunk person passing out in a small puddle. (PCP users frequently lose their sense of direction as well, and drowning is a major cause of death for them.) A few centimeters of water are sufficient for drowning if the victim lies face down on the water. Another cause of drownings are adverse weather and water and conditions, including waves and tidal or rivers currents. Drowning may also be due to strong negative buoyancy, where the victim is forced underwater by an object that is denser than water. Finally, drowning may be caused by another person forcing the victim under water, i.e. murder. 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)
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.
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 related not to the amount of oxygen in the blood but 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 hold their breath. This typically occurs at a 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.
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, 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.
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.
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 and is called secondary drowning. Inhaling certain poisonous vapors or gases will have a similar effect.
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.
Rescue and Treatment
Many pools and designated bathing areas either have either lifeguards, a pool safety camera system for local or remote monitoring, or computer aided drowning detection. However, bystanders play an important role in drowning detection and either intervention or the notification of authorities by phone or alarm.
If a drowning occurs or a swimmer becomes missing, bystanders should immediately call for help. The lifeguard should be called if present. If not, Emergency medical services and Paramedics should be contacted as soon as possible.
The first step in rescuing a drowning victim is to bring the victim's mouth and nose above the water surface. For further treatment it is advisable to remove the victim from the water. Conscious victims may panic and thus hinder rescue efforts. Often, a victim will cling to the rescuer and try to pull themselves out of the water, submerging the rescuer in the process. To avoid this, it is recommended that the rescuer approach the panicking victim with a buoyant object, or from behind, twisting the victim's arm on the back to restrict movement. If the victim pushes the rescuer under water, the rescuer should dive downwards to escape the victim.
After successfully approaching the victim, negatively buoyant objects such as a weight belt are removed. The priority is then to transport the victim to the water's edge in preparation for removal from the water. The victim is turned on his back. A secure grip is used to tow panicking victims from behind, with both rescuer and victim laying on their back, and the rescuer swimming a breaststroke kick. A cooperative victim may be towed in a similar fashion held at the armpits, and the victim may assist with a breaststroke kick. An unconscious victim may be pulled in a similar fashion held at the chin and cheeks, ensuring that the mouth and nose is well above the water.
There is also the option of pushing a cooperative victim lying on his back with the rescuer swimming on his belly and pushing the feet of the victim, or both victim and rescuer lying on the belly, with the victim hanging from the shoulders of the rescuers. This has the advantage that the rescuer can use both arms and legs to swim breaststroke, but if the victim pushes his head above the water, the rescuer may get pushed down. This method is often used to retrieve tired swimmers. If the victim wears lifejacket, buoyancy compensator, or other flotation device that stabilizes his position with the face up, only one hand of the rescuer is needed to pull the victim, and the other hand may provide forward movement or may help in rescue breathing while swimming, using for example a snorkel.
Special care has to be taken for victims with suspected spinal injuries, and a back board (spinal board) may be needed for the rescue. In water, CPR is very difficult, and the goal should be to bring the victim to a stable ground quickly and then to start CPR.
If the approach to a stable ground includes the edge of a pool without steps or the edge of a boat, special techniques have been developed for moving the victim over the obstacle. For pools, the rescuer stands outside, holds the victim by his hands, with the victims back to the edge. the rescuer then dips the victim into the water quickly to achieve an upward speed of the body, aiding with the lifting of the body over the edge. Lifting a victim over the side of a boat may require more than one person. Special techniques are also used by the Coast Guard and military for helicopter rescues.
After reaching dry ground, all victims should seek medical assistance, especially if unconscious or if even small amounts of water have entered the lungs. An unconscious victim may need artificial respiration or CPR.
The Heimlich maneuver is needed only for obstructed airways, not for water in the airways. Performing the Heimlich maneuver on drowning victims not only delays ventilation, it may induce vomiting - the vomit may then be aspirated, leading to serious injury or death. Furthermore, news articles have raised concerns that the entire concept is not only useless, but that Dr. Henry Heimlich used fabricated case reports to promote the idea: http://complaint.active.ws
100% Oxygen is highly recommended, including an intubation if necessary. Treatment for hypothermia may also be necessary. Water in the stomach need not be removed. Other injuries should also be treated (see first aid). Victims that are alert, awake, and intact have nearly a 100% survival rate.
Drowning victims should be treated even if they have been submerged for a long time. The rule "no patient should be pronounced dead until warm and dead" applies. Children in particular have a good chance of survival in water up to 3 minutes, or 10 minutes in cold water (10-15C or 50-60F). Submersion in cold water can slow the metabolism drastically. There are rare but documented cases of survivable submersion for extreme lengths of time. In one case a child survived drowning after being submerged in cold water for 70 minutes. In another, an 18 year old man survived 38 minutes under water. This is known as cold water drowning.
- Learn to swim and arrange for your family to learn to swim!
- Children should never be unsupervised while in or near water.
- Supervised swimming facilities with lifeguards should be preferred over swimming locations without supervision.
- Swimming alone should be avoided. Swim accompanied by a responsible adult.
- Never enter deep water if you cannot swim.
- Never rely on swimming aids, since they may fail.
- Never swim while drunk or after a big meal.
- Wear a lifejacket while enjoying water sports such as sailing, surfing, or canoeing.
- Pay attention to the weather and water conditions, especially currents. Currents always look weaker from the outside!
- Never pretend to be a drowning victim, unless all bystanders are informed that this is an exercise.
- Learn and practice water rescue if possible.
- Never dive into shallow or cloudy water. Always check depth and safety before diving. If you dive head first, stretch your arms to the front to reduce injuries to the head if there is a collision.
- Do not walk on frozen lakes, rivers or oceans unless the ice is thick enough over the entire area walked on
- Do not handle electric powered devices in or near the water.
- When boating, ensure your boat is operational and emergency equipment is onboard.
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