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Drowning
Drowning

Drowning is defined as respiratory impairment as a result of being in or under a liquid.[7][10] Drowning typically occurs silently, with only a few people able to wave their hands or call for help.[1] Symptoms following rescue may include breathing problems, vomiting, confusion, or unconsciousness.[2][3] Occasionally symptoms may not appear until up to six hours afterwards.[3] Drowning may be complicated by low body temperature, aspiration of vomit, or acute respiratory distress syndrome.[4][11]

Drowning is more common when the weather is warm and among those with frequent access to water.[4][5] Risk factors include alcohol use, epilepsy, and low socioeconomic status.[5] Common locations of drowning include swimming pools, bathtubs, natural bodies of water, and buckets.[3][7] Initially the person holds their breath, which is followed by laryngospasm, and then low oxygen levels.[4] Significant amounts of water typically only enter the lungs later in the process.[4] It may be classified into three types: drowning with death, drowning with ongoing health problems, and drowning with no ongoing health problems.[10]

Efforts to prevent drowning include teaching children to swim, safe boating practices, and limiting or removing access to water such as by fencing pools.[5][6] Treatment of those whose who are not breathing should begin with opening the airway and providing five breaths.[7] In those whose heart is not beating and who have been underwater for less than an hour CPR is recommended.[7] Survival rates are better among those with a shorter time under the water.[7] Among children who survive poor outcomes occur in about 7.5% of cases.[7]

In 2015, there were an estimated 4.5 million cases of unintentional drowning worldwide.[8] That year, there were 324,000 drowning deaths, making it the third leading cause from unintentional injuries after falls and motor vehicle collisions.[9] Of these deaths, 56,000 occurred in children less than five years old.[9] Drowning accounts for 7% of all injury related deaths, with more than 90% of these deaths occurring in developing countries.[5][9] Drowning occurs more frequently in males and the young.[5]

Signs and symptoms


Drowning is most often quick and unspectacular.

  • Head low in the water, mouth at water level
  • Head tilted back with mouth open
  • Eyes glassy and empty, unable to focus
  • Eyes open, with fear evident on the face
  • 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.

Drowning begins at the point a person is unable to keep their mouth above water; inhalation of water takes place at a later stage.[13] Most people demonstrating the instinctive drowning response do not show obvious prior evidence of distress.[13]

A person drowning is generally unable to call for help, or seek attention, as they cannot obtain enough air.

Cause


Approximately 90% of drownings take place in freshwater (rivers, lakes and swimming pools) and 10% in seawater. Drownings in other fluids are rare, and often relate to industrial accidents. In New Zealand's early colonial history, so many settlers died while trying to cross rivers that drowning was known as "The New Zealand death".[15]

People have drowned in as little as 30 mm of water lying face down.[16] 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:

  • Ascent blackout, also called deep water blackout – caused by latent hypoxia during ascent from depth, 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. It usually strikes upon arriving near the surface as the pressure approaches normal atmospheric pressure.[17]
  • Shallow water blackout – caused by hyperventilation prior to swimming or diving. The primary urge to breathe is triggered by rising carbon dioxide (CO2) levels in the bloodstream.[18] The body detects CO2 levels very accurately and relies on this to control breathing.[18] Hyperventilation reduces the carbon dioxide content of the blood but leaves the diver susceptible to sudden loss of consciousness without warning from hypoxia. There is no bodily sensation that warns a diver of an impending blackout, and victims (often capable swimmers swimming under the surface in shallow water) become unconscious and drown quietly without alerting anyone to the fact that there is a problem; they are typically found on the bottom.
  • Further complications following the drowning incident – Inhaled fluid can act as an irritant inside the lungs. Physiological responses to even small quantities include the extrusion of liquid into the lungs (pulmonary edema) over the following hours, but this reduces the ability to exchange air and can lead to a person "drowning in their own body fluid". Certain poisonous vapors or gases (as for example in chemical warfare), or vomit can have a similar effect. The reaction can take place up to 72 hours after the drowning incident, and may lead to a serious condition or death.

Populations groups at risk:[19]

  • In the US: Children and young adults: Drowning rates are highest for children under 5 years of age and persons 15–24 years of age.

Behavioral and physical factors:[19][20]

  • Worldwide, people with epilepsy are more likely to die due to accidents such as drowning.

Pathophysiology


Drowning can be considered as going through four stages:[23]

Generally, in the early stages of drowning a person holds their breath to prevent water from entering their lungs.[7] When this is no longer possible a small amount of water entering the trachea causes a muscular spasm that seals the airway and prevents further passage of water.[7] If the process is not interrupted, loss of consciousness due to hypoxia is followed rapidly by cardiac arrest.

A conscious person 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 person can voluntarily hold his or her breath for some time, but the breathing reflex will increase until the person tries to breathe, even when submerged.[24]

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 person 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 between people.

The breath-hold break point can be suppressed or delayed either intentionally or unintentionally.

A continued lack of oxygen in the brain, hypoxia, will quickly render a person unconscious usually around a blood partial pressure of oxygen of 25–30 mmHg.[26] An unconscious person 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 person stands a good chance of recovery if attended to within minutes. More than 10% of drownings may involve laryngospasm, but the evidence suggests that it is not usually effective at preventing water from entering the trachea. The lack of water found in lungs during autopsy does not necessarily mean there was no water at the time of drowning, as small amounts of freshwater are readily absorbed into the bloodstream. Hypercarbia and hypoxia both contribute to laryngeal relaxation, after which the airway is effectively open through the trachea. There is also bronchospasm and mucous production in the bronchi associated with laryngospasm, and these may prevent water entry at terminal relaxation.[27]

The hypoxemia and acidosis caused by asphyxia in drowning affect various organs.

A lack of oxygen or chemical changes in the lungs may cause the heart to stop beating.

The extent of central nervous system injury to a large extent determines the survival and long term consequences of drowning, In the case of children, most survivors are found within 2 minutes of immersion, and most fatalities are found after 10 minutes or more.[28]

If water enters the airways of a conscious person, the person will try to cough up the water or swallow it, often inhaling more water involuntarily. When water enters the larynx or trachea, both conscious and unconscious persons experience laryngospasm, in which the vocal cords constrict, sealing the airway. This prevents water from entering the lungs. Because of this laryngospasm, in the initial phase of drowning, water generally enters the stomach and very little water enters the lungs. Though laryngospasm prevents water from entering the lungs, it also interferes with breathing. In most persons, the laryngospasm relaxes some time after unconsciousness and water can then enter the lungs causing a "wet drowning". However, about 7–10% of people maintain this seal until cardiac arrest.[24] This has been called "dry drowning", as no water enters the lungs. In forensic pathology, water in the lungs indicates that the person 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.[29]

Aspirated water that reaches the alveoli destroys the pulmonary surfactant, which causes pulmonary oedema and decreased lung compliance which compromises oxygenation in affected parts of the lungs. This is associated with metabolic acidosis, and secondary fluid and electrolyte shifts. During alveolar fluid exchange, diatoms present in the water may pass through the alveolar wall into the capillaries to be carried to internal organs. Presence of these diatoms may be diagnostic of drowning.

Of people who have survived drowning, almost one third will experience complications such as acute lung injury (ALI) or acute respiratory distress syndrome (ARDS).[30] ALI/ARDS can be triggered by pneumonia, sepsis and water aspiration and are life-threatening disorders that can result in death if not treated promptly.[30] During drowning, aspirated water enters the lung tissues, causes a reduction in alveolar surfactant, obstructs ventilation and triggers a release of inflammatory mediators which ultimately results in hypoxia.[30] Specifically, upon reaching the alveoli, hypotonic liquid found in fresh water dilutes pulmonary surfactant, destroying the substance.[31] Comparatively, aspiration of hypertonic seawater draws liquid from the plasma into the alveoli and similarly causes damage to surfactant by disrupting the alveolar-capillary membrane.[31] Still, there is no clinical difference between salt and freshwater drowning. Once someone has reached definitive care, supportive care strategies such as mechanical ventilation can help to reduce the complications of ALI/ARDS.[30]

Whether a person drowns in fresh water versus salt water makes no difference in the respiratory management or the outcome of the person.[32] People who drown in fresh water may experience worse hypoxemia early in their treatment, however, this initial difference is short-lived and the management of both fresh water and salt water drowning is essentially the same.[32]

Submerging the face in water cooler than about 21 °C (70 °F) triggers the diving reflex, common to air-breathing vertebrates, especially 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:

  • Bradycardia, a slowing of the heart rate by up to 50% in humans.
  • 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 actual cause of death in cold or very cold water is usually lethal bodily reactions to increased heat loss and to freezing water, rather than any loss of core body temperature. Of those who die after plunging into freezing seas, around 20% 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),[35] and exhaustion and unconsciousness cause drowning, claiming the rest within a similar time.[36] 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.[37]

Submersion into cold water can induce cardiac arrhythmias (abnormal heart rates) in healthy people, sometimes causing strong swimmers to drown.[38] The physiological effects caused by the diving reflex conflict with the body's cold shock response, which includes a gasp and uncontrollable hyperventilation leading to aspiration of water.[39] While breath-holding triggers a slower heart rate, cold shock activates tachycardia, an increase in heart rate.[38] It is thought that this conflict of these nervous system responses may account for the arrhythmias of cold water submersion.[38]

Heat transfers very well into water, and body heat is therefore lost extremely quickly in water compared to air,[40] even in merely 'cool' swimming waters around 70F (~20C).[36] 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.[36] 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.

Upon submersion into cold water, remaining calm and preventing loss of body heat is paramount.[41] While awaiting rescue, swimming or treading water should be limited to conserve energy and the person should attempt to remove as much of the body from the water as possible; attaching oneself to a buoyant object can improve the chance of survival should unconsciousness occur.[41]

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.

Most victims of cold-water drowning do not develop hypothermia quickly enough to decrease cerebral metabolism before ischemia and irreversible hypoxia occur.

Diagnosis


The World Health Organization in 2005 defined drowning as "the process of experiencing respiratory impairment from submersion/immersion in liquid".[10] This definition does not imply death, or even the necessity for medical treatment after removal of the cause, nor that any fluid enters the lungs.

Experts differentiate between distress and drowning.

  • Distress – people in trouble, but who still have the ability to keep afloat, signal for help and take actions.
  • Drowning – people suffocating and in imminent danger of death within seconds.

Forensic diagnosis of drowning is considered one of the most difficult in forensic medicine.

Drowning would be considered as a possible cause of death when the body was recovered from a body of water, or in close proximity to a fluid which could plausibly have caused drowning, or when found with the head immersed in a fluid.

Diatoms should normally never be present in human tissue unless water was aspirated, and their presence in tissues such as bone marrow suggests drowning, however, they are present in soil and the atmosphere and samples may easily be contaminated. An absence of diatoms does not rule out drowning, as they are not always present in water.[23] A match of diatom shells to those found in the water may provide supporting evidence of the place of death.[43] Drowning in salt water can leave significantly different concentrations of sodium and chloride ions in the left and right chambers of the heart, but this will dissipate if the person survived for some time after the aspiration, or if CPR was attempted,[23] and have been described in other causes of death.[43]

Most autopsy findings relate to asphyxia and are not specific to drowning.

Prevention


Most drowning is preventable.

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.

Lifeguards may be unaware of a drowning due to "failure to recognize the struggle, the intrusion of non-lifeguard duties upon lifeguards' primary task-preventive lifeguarding, and the distraction from surveillance duties".[45]

Pool alarms have poor evidence for any utility.[7]

Management


Many people who are drowning manage to save themselves, or are assisted by bystanders or professional rescuers.

Rescue involves bringing the person's mouth and nose above the water surface.

Where it is necessary to approach a panicking person in deep water, 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 can dive downwards to escape.

After a successful approach, negatively buoyant objects such as a weight belt are removed.

Rescue, and where necessary, resuscitation, should be started as early as possible.

The checks for responsiveness and breathing are carried out with the person horizontally supine.

Attempts to actively expel water from the airway by abdominal thrusts, Heimlich maneuver or positioning head downwards should be avoided as there is no obstruction by solids, and they delay the start of ventilation and increase the risk of vomiting, with a significantly increased risk of death, as aspiration of stomach contents is a common complication of resuscitation efforts.[44][48]

Treatment for hypothermia may also be necessary. However, in those who are unconscious, it is recommended their temperature not be increased above 34 degrees C.[11] Because of the diving reflex, people submerged in cold water and apparently drowned may revive after a relatively long period of immersion.[49] Rescuers retrieving a child from water significantly below body temperature should attempt resuscitation even after protracted immersion.[49]

People with a near-drowning experience who have normal oxygen levels and no respiratory symptoms should be observed in a hospital environment for a period of time to ensure there are no delayed complications.[50] The target of ventilation is to achieve 92% to 96% arterial saturation and adequate chest rise.

While surfactant may be used no high quality evidence exist that looks at this practice.[3] Extracorporeal membrane oxygenation may be used in those who cannot be oxygenated otherwise.[3] Steroids are not recommended.[3]

Prognosis


People who have drowned who arrive at a hospital with spontaneous circulation and breathing usually recover with good outcomes.[49] Early provision of basic and advanced life support improve probability of positive outcome.[44]

Longer duration of submersion is associated with lower probability of survival and higher probability of permanent neurological damage.[49]

Contaminants in the water can cause bronchospasm and impaired gas exchange, and can cause secondary infection with delayed severe respiratory compromise.[49]

Low water temperature can cause ventricular fibrillation, but hypothermia during immersion can also slow the metabolism, allowing a longer hypoxia before severe damage occurs.[49] Hypothermia which reduces brain temperature significantly can improve outcome.

The younger the victim, the better the chances of survival.[49] In one case, a child submerged in cold (37 °F (3 °C)) water for 66 minutes was resuscitated without apparent neurological damage.[49] However, over the long term significant deficits were noted, including a range of cognitive difficulties, particularly general memory impairment, although recent magnetic resonance imaging (MRI) and magnetoencephalography (MEG) were within normal range.[51]

Drowning is a major worldwide cause of death and injury in children.

Data on long-term outcome are scarce and unreliable.

Epidemiology


In 2013, drowning was estimated to have resulted in 368,000 deaths, down from 545,000 deaths in 1990.[54] There are more than 20 times that many non-fatal incidents.[55] It is the third leading cause of death from unintentional trauma after traffic injuries and falls.[56]

In many countries, drowning is one of the main causes of preventable death for children under 12 years old. In the United States in 2006, 1100 people under 20 years of age died from drowning.[57] The United Kingdom has 450 drownings per year, or 1 per 150,000, whereas in the United States, there are about 6,500 drownings yearly, around 1 per 50,000. In Asia suffocation and drowning were the leading causes of preventable death for children under five years of age;[58][59] a 2008 report by the organization found that in Bangladesh, for instance, 46 children drown each day.[60]

Males, due to a generally increased likelihood for risk taking, are 4 times more likely to have submersion injuries.[55]

In the fishing industry, the largest group of drownings is associated with vessel disasters in bad weather, followed by man-overboard incidents and boarding accidents at night; either in foreign ports, or under the influence of alcohol.[55] Scuba diving deaths are estimated at 700 to 800 per year, associated with inadequate training and experience, exhaustion, panic, carelessness and barotrauma.[55]

In the United States, drowning is the second leading cause of death (after motor vehicle accidents) in children 12 and younger.[61]

People who drown are more likely to be male, young, or adolescent.[61] Surveys indicate that 10% of children under 5 have experienced a situation with a high risk of drowning.

According to the US National Safety Council, 353 people ages 5 to 24 drowned in 2017.[64]

Society and culture


The word "drowning"—like "electrocution"—was previously used to describe fatal events only, and occasionally that usage is still insisted upon, though the consensus of the medical community supports the definition used in this article.

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.[10][44] 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.[12]

Dry drowning:Drowning in which no water enters the lungs[10][44]

Near drowning: Drowning which is not fatal[10][44]

Wet drowning: Drowning in which water enters the lungs[10][44]

Passive drowning: People who suddenly sink or have sunk due to a change in their circumstances.

Secondary drowning: Physiological response to foreign matter in the lungs due to drowning causing extrusion of liquid into the lungs (pulmonary edema) which adversely affects breathing[10][44]

Silent drowning: Drowning without a noticeable external display of distress.[10][65]

Dry drowning is a term that has never had an accepted medical definition, and that is currently medically discredited.[66][44] Following the 2002 World Congress on Drowning in Amsterdam, a consensus definition of drowning was established. Based on this definition, drowning is the "process of experiencing respiratory impairment from submersion/immersion in liquid."[68] This definition resulted in only three legitimate drowning subsets: fatal drowning, non-fatal drowning with illness/injury, and non-fatal drowning without illness/injury.[69] In response, major medical consensus organizations have adopted this definition worldwide and have officially discouraged any medical or publication use of the term "dry drowning".[66] Such organizations include the International Liaison Committee on Resuscitation,[70] the Wilderness Medical Society,[41] the American Heart Association,[71] the Utstein Style system,[70] the International Lifesaving Federation,[72] the International Conference on Drowning,[68] Starfish Aquatics Institute,[73] the American Red Cross,[74] the Centers for Disease Control and Prevention (CDC),[75][76][77] the World Health Organization [78] and the American College of Emergency Physicians.[79]

Drowning experts have recognized that the end result pathophysiology of hypoxemia, acidemia, and eventual death is the same whether water entered the lung or not.

"Dry drowning" is frequently cited in the news with a wide variety of definitions.[81] and is often confused with the equally inappropriate and discredited term "secondary drowning" or "delayed drowning".[82] Various conditions including spontaneous pneumothorax, chemical pneumonitis, bacterial or viral pneumonia, head injury, asthma, heart attack, and chest trauma have been misattributed to the erroneous terms "delayed drowning", "secondary drowning", and "dry drowning". Currently, there has never been a case identified in the medical literature where a person was observed to be without symptoms and who died hours or days later as a direct result of drowning alone.[66]

In Europe, drowning was used as capital punishment. During the Middle Ages, a sentence of death was read using the words "cum fossa et furca", or "with pit and gallows".[83]

Drowning survived as a method of execution in Europe until the 17th and 18th centuries.[84] 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.

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