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Drowning is death caused by the filling of the lungs by a liquid causing the interruption of the body's exchange of oxygen from the air leading to asphyxia. It also includes death caused by filling of the lungs with a hypotonic solution (eg. fresh water) which causes ventricular fibrillation before asphyxia occurs.
Near drowning is the survival of a drowning event involving unconsciousness or significant water inhalation and can lead to serious secondary complications, including death, after the event. Cases of near drowning therefore also require attention by medical professionals.
Secondary drowning is death due to chemical or biological changes in the lungs after a near drowning incident.
In many countries, drowning is one of the leading causes of death for children under 14 years old. The rate of drowning in populations around the world varies widely according to their access to water, the climate and the national swimming culture. For example, typically the United Kingdom suffers 450 drownings per annum or 1 per 150,000 of population whereas the United States suffers 6,500 drownings or around 1 per 50,000 of population. Drowning related injuries are the fifth most likely cause of accidental death in the US. In some regions, drowning is the second most likely cause of injury and death for children after car accidents. The rate of near drowning incidents is unknown. Victims are more likely to be male, young or adolescent. Surveys indicate that 10% of children under 5 have experienced a situation with a high risk of drowning. The causes of drowning cases in the US are as follows:
- 44% are related to swimming
- 17% are related to boating
- 14% are unattributed
- 10% related to scuba diving
- 7% related to car accidents
Drowning risk situations
Most drownings occur in water, 90% in freshwater (rivers and lakes) 10% in seawater, drownings in other fluids are rare and often industrial accidents. 
Common conditions that may lead to drowning include but are not limited to:
- Water conditions exceed the swimmer's ability; - turbulent or fast water, water out of depth, falling through ice, rip currents, undertows, currents, waves and eddies.
- Entrapment; - physically unable to get out of the situation because of a lack of an escape route, snagging or by being hampered by clothing or equipment.
- Impaired judgement and physical incapacitation arising from the use of drugs, principally alcohol.
- Incapacitation arising from the conditions; - cold (hypothermia), shock, injury or exhaustion.
- Incapacitation arising from acute illness while swimming; - heart attack, seizure or stroke.
- Forcible submersion by another person; - murder or misguided children's play.
- Blackout underwater after rapid breathing to extend a breath-hold dive; - shallow water blackout.
- Blackout on ascent from a deep breath-hold dive due to latent hypoxia; - deep water blackout.
People have drowned in as little as 30mm of water lying face down, in one case in a wheel rut. Children have drowned in baths, buckets and toilets, inebriates or those under the influence of drugs have died in puddles. For a more detailed list of causes see swimming.
The physiology of drowning
The body's reaction to submersion
Submerging the face in water triggers the mammalian diving reflex This is found in all mammals, and especially in marine mammals such as whales and seals. This reflex is designed to protect the body by putting it into energy saving mode to maximize the time it can stay under water. The effect of this reflex is greater in cold water than in warm water and has three principal effects:
- Bradycardia, a slowing of 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, the region of the chest between the diaphragm and the neck, to avoid the collapse of the lungs under higher pressure during deeper dives.
The reflex action is automatic and allows both a conscious and an unconscious person to survive longer without oxygen under water than in a comparable situation on dry land.
The reaction to oxygen deprivation
A conscious victim will hold his 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 his 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 his breath. This typically occurs at an arterial partial pressure of carbon dioxide of 55 mm Hg, but may differ significantly from individual to individual and can be increased through training.
The breath-hold break point can be suppressed or delayed either intentionally or unintentionally. Hyperventilation before any dive, deep or shallow, flushes out carbon dioxide in the blood resulting in a dive commencing with an abnormally low carbon dioxide level; a potentially dangerous condition known as hypocapnia. The level of carbon dioxide in the blood after hyperventilation may then be insufficient to trigger the breathing reflex later in the dive and a blackout may occur without warning and before the diver feels any urgent need to breathe. This can occur at any depth and is common in distance breath-hold divers in swimming pools, refer to shallow water blackout for more detail. Hyperventilation is often used by both deep and distance free-divers to flush out carbon dioxide from the lungs to suppress the breathing reflex for longer. It is important not to mistake this for an attempt to increase the body's oxygen store. The body at rest is fully oxygenated very quickly by normal breathing and cannot take on any more. Breath holding in water should always be supervised by a second person, as by hyperventilating, one increases the risk of shallow water blackout because insufficient carbon dioxide levels in the blood fail to trigger the breathing reflex.
The reaction to water inhalation
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 experience laryngospasm, that is 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 causing a "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 indicates that the victim was still alive at the point of submersion; the absence of water in the lungs may be either a dry drowning or indicates a death before submersion.
A continued lack of oxygen in the brain, hypoxia, will quickly render a victim unconscious usually around a blood partial pressure of oxygen of 25-30mmHg. An unconscious victim rescued with an airway still sealed due to laryngospasm stands a good chance of a full recovery. Artificial respiration is also much more effective without water in the lungs. At this point the victim stands a good chance of recovery if attended to within minutes. In most victims the laryngospasm relaxes some time after unconsciousness and water fills the lungs resulting in a wet drowning. Latent hypoxia is a special condition leading to unconsciousness where the partial pressure of oxygen in the lungs under pressure at the bottom of a deep free-dive is adequate to support consciousness but drops below the blackout threshold as the water pressure decreases on the ascent, usually close to the surface as the pressure approaches normal atmospheric pressure. A blackout on ascent like this is called a deep water blackout.
Cardiac arrest and death
The brain cannot survive long without oxygen and the continued lack of oxygen in the blood combined with the cardiac arrest will lead to the deterioration of brain cells causing first brain damage and eventually brain death from which recovery is generally considered impossible. A lack of oxygen or chemical changes in the lungs may cause the heart to stop beating; this cardiac arrest stops the flow of blood and thus stops the transport of oxygen to the brain. Cardiac arrest used to be the traditional point of death but at this point there is still a chance of recovery. The brain will die after approximately six minutes without oxygen but special conditions may prolong this (see 'cold water drowning' below). Freshwater contains less salt than blood and will therefore be absorbed into the blood stream by osmosis. In animal experiments this was shown to change the blood chemistry and led to cardiac arrest in 2 to 3 minutes. Sea water is much saltier than blood through osmosis water will leave the blood stream and enter the lungs thickening the blood. 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. After death rigor mortis will set in and remains for about two days, depending on many factors including water temperature.
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.
Rescue and treatment
Many pools and designated bathing areas either have 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. No person should attempt a rescue that is beyond his or her ability or level of training.
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 himself 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.
Actively drowning victims do not usually call out for help simply because they lack the air to do so. It is necessary to breathe to yell. Human physiology does not allow the body to waste any air when starving for it. They rarely raise their hands out of the water. They use the surface of the water to push themselves up in an attempt to get their mouths out of the water. Lifting arms out of the water always pushes the head down. Head low in the water, occasionally bobbing up and down is another common sign of active drowning.
There can be splashing involved during drowning, usually a butterfly like stroke where the hands barely clear the waters surface, and sometimes victims can look like they are climbing an invisible ladder in the water. These presentations, however, are not the most common.
Extenuating factors such as increased levels of stress, secondary injuries, and environmental factors can increase the likelihood of distress and/or drowning in persons who end up overboard. It is important that you recognize the behaviors associated with aquatic distress and drowning, so you can make informed decisions during emergencies.
Signs or behaviors associated with drowning or near-drowning:
- Head low in the water, mouth at water level
- Head tilted back with mouth open
- Eyes glassy and empty, unable to focus
- Eyes closed
- Hair over forehead or eyes
- Hyperventilating or gasping
- Trying to swim in a particular direction but not making headway
- Trying to roll over on the back to float
- Uncontrollable movement of arms and legs, rarely out of the water.
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 be referred to 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 manoeuver is not recommended; the technique may have relevance in situations where airways are obstructed by solids but not fluids. Performing the manoeuver on drowning victims not only delays ventilation but may induce vomiting, which if aspirated will place the patient in a far worse situation. Moreover, the use of the Heimlich manoeuvre in any choking situation, involving solids or fluids, has become controversial and is generally no longer taught. For more information on this debate refer to the article Henry Heimlich.
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, except in the case of paediatric drownings as a gastric distension can limit movement of the lungs. 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 to 15 °C or 50 to 60 °F). 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.
The reduction of drowning through education has become a significant element of school curricula and is integrated into most water sports training. The elements incoporated into this training vary according to the particular context but tend to pick from the following generic list:
- Learn to swim
- Learn and practice water rescue.
- Know your strengths and limitations in the water.
- Stay within your depth if you are not a strong swimmer.
- Keep a watch out for others.
- Swim with company, find a buddy, children swim with a responsible adult.
- Ensure that children have competent supervision in or near water.
- Swim in areas supervised by lifeguards in preference to areas without.
- Be cautious and very conservative when swimming at night.
- Ensure that your boat is reliable, properly loaded and that functional emergency equipment is onboard.
- Wear a properly fitting lifejacket while enjoying water sports such as sailing, surfing or canoeing.
- Pay attention to the weather, tides and water conditions, especially currents. Currents always look weaker from the outside!
- Never swim while drunk or on drugs.
- Never hyperventilate to extend a breathe-hold dive, see deep and shallow water blackout
- Never rely on swimming aids, they may fail.
- Never play games that will put your life, or others', at risk.
- Never pretend to be a drowning victim, unless ALL bystanders are informed that this is an exercise.
- Never dive into water where you cannot clearly see the bottom or do not know the depth.
- Never walk on ice unless you know absolutely that the ice is thick enough over the entire route.
- Never handle electrical devices in or near the water.
- Never exceed your limits.
- Never swim in cold water.
- List of drowning victims
- Medical emergency
- Artificial respiration
- Shallow water blackout
- Deep water blackout
- Diver rescue
- Dry drowning
- Drowning prevention information from Seattle Children's Hospital.
- Drowning prevention and water safety information from the Washington State Drowning Prevention Network
- emedicine.com article
- Med+NC Show (RTP-TV 2003) Online video about saving drowning victims
- Information on search and recovery of drowning victims