出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/10/30 17:27:23」(JST)
| Drowning / Near drowning | |
|---|---|
| Classification and external resources | |
Vasily Perov: The drowned, 1867
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| ICD-10 | T75.1 |
| ICD-9 | 994.1 |
| DiseasesDB | 3957 |
| MedlinePlus | 000046 |
| eMedicine | emerg/744 |
| MeSH | C23.550.260.393 |
Drowning is the process of experiencing respiratory impairment from submersion/immersion in liquid. Near drowning is the survival of a drowning event involving unconsciousness or water inhalation and can lead to serious secondary complications or death, possibly up to 72 hours after the event.[1][2] It occurs more frequently in males and the young.[3]
Drowning itself is quick and silent, although it may be preceded by distress which is more visible.[4] A person drowning is unable to shout or call for help, or seek attention, as they cannot obtain enough air. The instinctive drowning response is the final set of autonomic reactions in the 20 – 60 seconds before sinking underwater, and to the untrained eye can look similar to calm safe behavior.[4][5] Lifeguards and other persons trained in rescue learn to recognize drowning people by watching for these instinctive movements.[4]
Drowning is the 3rd leading cause of unintentional injury death worldwide, accounting for 7% of all injury related deaths (est. 388,000 deaths by drowning in 2004, excluding those due to natural disasters), with 96% of these deaths occurring in low-income and middle-income countries.[6] In many countries, drowning is one of the leading causes of death for children under 12 years old. For example, in the United States, it is the second leading cause of death (after motor vehicle crashes) in children 12 and younger.[3] The rate of drowning in populations around the world varies widely according to their access to water, the climate and the national swimming culture.
The following definition was accepted by the World Congress on Drowning in 2002[7] and subsequently by the World Health Organisation in 2005: "Drowning is the process of experiencing respiratory impairment from submersion/immersion in liquid."[8] This definition does not imply fatality, or even the necessity for medical treatment after removal of the cause, nor that any fluid necessarily enters the lungs. The WHO further recommended "Drowning outcomes should be classified as: death, morbidity, and no morbidity. There was also consensus that the terms wet, dry, active, passive, silent, and secondary drowning should no longer be used."[8]
Experts differentiate between distress and drowning. They also divide drowning into passive and active:
Active drowning – people such as non-swimmers and the exhausted or hypothermic at the surface, who are unable to hold their mouth above water and are suffocating due to lack of air. Instinctively, people in such cases perform well known behaviors in the last 20–60 seconds before being submerged, representing the body's last efforts to obtain air. Notably such people are unable to call for help, talk, reach for rescue equipment, or alert swimmers even feet away, and they may drown quickly and silently close to other swimmers or safety.[citation needed]
Drowning is most often quick and unspectacular. Its media depictions as a loud, violent struggle have much more in common with distressed non-swimmers, who may well drown but have not yet begun. In particular, an asphyxiating person is seldom able to call for help.[9] The instinctive drowning response covers many signs or behaviors associated with drowning or near-drowning:
Pia notes that drowning begins at the point a person is unable to keep their mouth above water; inhalation of water takes place at a later stage.[10] Most people demonstrating the instinctive drowning response do not show prior evidence of distress.[10]
Approximately 90% of drownings take place in freshwater (rivers, lakes and swimming pools) and 10% in seawater. Drownings in other fluids is rare, and often relates to industrial accidents.[citation needed]
People have drowned in as little as 30 mm of water lying face down, in at least one case in a wheel rut.[citation needed] Children have drowned in baths, buckets and toilets; inebriates or those under the influence of drugs have died in puddles.
Drowning can also happen in ways that are less well known:
A continued lack of oxygen in the brain, hypoxia, will quickly render a victim unconscious usually around a blood partial pressure of oxygen of 25–30 mmHg. An unconscious victim rescued with an airway still sealed from 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. 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.
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 Reflex reactions to immersion and cold water immersion below).
As well as the direct effect of oxygen deprivation, there are also dangerous effects on blood chemistry if water is taken into the lungs. The mechanism for this is different for fresh and seawater.
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.
Submerging the face in water colder than about 21 °C (70 °F) triggers the mammalian diving reflex, found in mammals, and especially in marine mammals such as whales and seals. This reflex protects the body by putting it into energy saving mode to maximize the time it can stay under water. The strength of this reflex is greater in colder water and has three principal effects:
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 exact mechanism for this effect has been debated and may be a result of brain cooling similar to the protective effects seen in patients treated with deep hypothermia.[12][13]
In very cold or freezing water reflex reactions can be lethal instead, killing up to 70% of people within 15–30 minutes, as they give rise first to cold shock, a combination of uncontrolled gasping and massively increased blood pressure with possible cardiac arrest, followed by the rapid loss of control of bodily functions needed for swimming and gripping. (see cold water immersion below)
A conscious victim will hold his or her 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 or her breath for some time, but the breathing reflex will increase until the victim will try to breathe, even when submerged.[14]:702
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 (see Hypercapnia). During apnea, the oxygen in the body is used by the cells, and excreted as 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 or her 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. 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 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.
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. Because of this laryngospasm, water enters the stomach in the initial phase of drowning and very little water enters the lungs. Unfortunately, this can interfere with air 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 7–10% of victims maintain this seal until cardiac arrest.[14] This was 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. Absence of water in the lungs may be either a dry drowning or indicates a death before submersion.[15]
"[S]omething that almost no one in the maritime industry understands ... That includes mariners [and] even many (most) rescue professionals: It is impossible to get hypothermic in cold water unless you are wearing flotation, because without flotation you won’t live long enough to become hypothermic."
— Mario Vittone, lecturer and author in water rescue and survival[16] [Emphasis in original]
Cold water has a number of effects on drowning and survival. Hypothermia (loss of core body temperature) is the best known, but the body can endure lowered temperatures for a considerable time, and also protects itself by moving blood circulation to protect the core.
Heat transfers very well through water, and body heat is therefore lost extremely quickly in water compared to land,[17] even in merely 'cool' swimming waters around 70F (~20C).[18] A water temperature of 10 °C (50 °F) can lead to death in as little as one hour, and water temperatures hovering at freezing can lead to death in as little as 15 minutes.[18] This is because cold water can have other lethal effects on the body, so hypothermia is not usually a reason for drowning or the clinical cause of death for those who drown in cold water.
The actual cause of death in cold or very cold water are usually lethal bodily reactions to increased heat loss and to freezing water, rather than any loss of core body temperature. For example, plunged into freezing seas, around 20% of victims die within 2 minutes from cold shock (uncontrolled rapid breathing and gasping causing water inhalation, massive increase in blood pressure and cardiac strain leading to cardiac arrest, and panic), another 50% die within 15 – 30 minutes from cold incapacitation (loss of use and control of limbs and hands for swimming or gripping, as the body 'protectively' shuts down the peripheral muscles of the limbs to protect its core),[16] and exhaustion and unconsciousness cause drowning, claiming the rest within a similar time.[18] A notable example of this occurred during the sinking of the Titanic, in which most people who entered the −2 °C (28 °F) water died within 15–30 minutes.[19]
Hypothermia (and also cardiac arrest) present a risk for survivors of immersion, as for survivors of exposure; in particular the risk increases if the survivor, feeling well again, tries to get up and move, not realizing their core body temperature is still very low and will take a long time to recover.
Rescue involves bringing the person's mouth and nose above the water surface. A drowning person may cling to the rescuer and try to pull himself out of the water, submerging the rescuer in the process. Thus it is advised that the rescuer approach with a buoyant object, or from behind, twisting the person's arm on the back to restrict movement. If the rescuer does get pushed under water, they should dive downwards to escape the person.
After a successful approach, negatively buoyant objects such as a weight belt are removed. The priority is then to transport the person to the water's edge in preparation for removal from the water. The person is turned on their back with a secure grip used to tow from behind. If the person is cooperative they may be towed in a similar fashion held at the armpits. If the person is unconscious they may be pulled in a similar fashion held at the chin and cheeks, ensuring that the mouth and nose are well above the water.
Special care has to be taken for people with suspected spinal injuries, and a back board (spinal board) may be needed for the rescue. In water, CPR is ineffective, and the goal should be to bring the person to a stable ground quickly and then to start CPR. Once on ground chest compressions are performed by the "A-B-C" scheme (Airway opening-Breaths-Compressions).[20] 100% oxygen is neither recommended nor discouraged.[21] Treatment for hypothermia may also be necessary.
The Heimlich maneuver is not recommended;[22] the technique may have relevance in situations where airways are obstructed by solids but not fluids. Performing the maneuver on drowning people 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 maneuver 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.
Because of the mammalian diving reflex (see above), person submerged in cold water and apparently drowned may revive after a relatively long period. In one case, a child submerged in cold (37 °F (3 °C)) water for 66 minutes was resuscitated without neurological damage.[23] Rescuers retrieving a child from water significantly below body temperature should attempt resuscitation even after protracted immersion.[23]
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.
The acronym RID was originated by Frank Pia to summarize important reasons why lifeguards may be unaware of a drowning. The term stands for "failure to recognize the struggle, the intrusion of non-lifeguard duties upon lifeguards' primary task-preventive lifeguarding, and the distraction from surveillance duties".[24] In his paper on the RID factors,[24] Pia makes a number of observations on the role, and the required behavior and training, of lifeguards, as well as the importance of administrators directing lifeguards to this role and avoiding double tasking them (due to the very brief time of 20 – 60 seconds required for drowning to occur). He ended by summarizing the role of lifeguards as guardians of life, and that they should be directed exclusively to this duty and none other, while on surveillance, due to the high value placed on human life.
Disability-adjusted life year for drowning per 100,000 inhabitants in 2004.[25]
Drowning resulted in 350,000 deaths in 2010, down from 430,000 deaths in 1990, making it the third leading cause of death from unintentional trauma after traffic injuries and falls.[26]
In the United States in 2006, 1100 people under 20 years of age died from drowning.[27] 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. In Asia, according to a study by The Alliance for Safe Children, suffocation and drowning were the most easily preventable causes of death for children under five years of age;[28][29] a 2008 report by the organization found that in Bangladesh, for instance, 46 children drown each day.[30]
People who drown are more likely to be male, young or adolescent.[3] Surveys indicate that 10% of children under 5 have experienced a situation with a high risk of drowning. About 175,000 children die through drowning every year.[31] The causes of drowning cases in the US from 1999 to 2006 are as follows:[32]
31.0% Drowning and submersion while in natural water
27.9% Unspecified drowning and submersion
14.5% Drowning and submersion while in swimming pool
9.4% Drowning and submersion while in bathtub
7.2% Drowning and submersion following fall into natural water
6.3% Other specified drowning and submersion
2.9% Drowning and submersion following fall into swimming pool
0.9% Drowning and submersion following fall into bathtub
In Europe, drowning was used as capital punishment. In fact, during the Middle Ages, a sentence of death was read using the words "cum fossa et furca", or "with drowning-pit and gallows." Furthermore, drowning was used as a way to determine if a woman were a witch. The idea was that witches would float and innocent women would drown. For more details, see trial by drowning. It is understood that drowning was used as the least brutal form of execution, and was therefore reserved primarily for women, although favored men were executed in this way, as well.
Drowning survived as a method of execution in Europe until the 17th and 18th centuries.[33] England had abolished the practice by 1623, Scotland by 1685, Switzerland in 1652, Austria in 1776, Iceland in 1777, and Russia by the beginning of the 1800s. France revived the practice during the French Revolution (1789–1799) and was carried out by Jean-Baptiste Carrier at Nantes.[34]
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| リンク元 | 「溺死」「水死」 |