Drowning


Drowning is a type of suffocation induced by the submersion of the mouth and nose in a liquid. Submersion injury refers to both drowning and near-miss incidents. Most instances of fatal drowning occur alone or in situations where others present are either unaware of the victim's situation or unable to offer assistance. After successful resuscitation, drowning victims may experience breathing problems, confusion, or unconsciousness. Occasionally, victims may not begin experiencing these symptoms until several hours after they are rescued. An incident of drowning can also cause further complications for victims due to low body temperature, aspiration, or acute respiratory distress syndrome.
Drowning is more likely to happen when spending extended periods near large bodies of water. Risk factors for drowning include alcohol use, drug use, epilepsy, minimal swim training or a complete lack of training, and, in the case of children, a lack of supervision. Common drowning locations include natural and man-made bodies of water, bathtubs, and swimming pools.
Drowning occurs when a person spends too much time with their nose and mouth submerged in a liquid to the point of being unable to breathe. If this is not followed by an exit to the surface, low oxygen levels and excess carbon dioxide in the blood trigger a neurological state of breathing emergency, which results in increased physical distress and occasional contractions of the vocal folds. When significant amounts of water enter the lungs, it is most often later in the process.
While the word "drowning" is commonly associated with fatal results, drowning may be classified into three different types: drowning that results in death, drowning that results in long-lasting health problems, and drowning that results in no health complications. Sometimes the term "near-drowning" is used in the latter cases. Among children who survive, health problems occur in about 7.5% of cases.
Steps to prevent drowning include teaching children and adults to swim and to recognise unsafe water conditions, never swimming alone, use of personal flotation devices on boats and when swimming in unfavourable conditions, limiting or removing access to water, and exercising appropriate supervision. Treatment of victims who are not breathing should begin with opening the airway and providing five breaths of mouth-to-mouth resuscitation. Cardiopulmonary resuscitation is recommended for a person whose heart has stopped beating and has been underwater for less than an hour.

Causes

A major contributor to drowning is the inability to swim. Other contributing factors include the state of the water itself, distance from a solid footing, physical impairment, or prior loss of consciousness. Anxiety brought on by fear of drowning or water itself can lead to exhaustion, thus increasing the chances of drowning.
Approximately 90% of drownings take place in freshwater ; the remaining 10% take place in seawater. Drownings in other fluids are rare and often related to industrial accidents. In New Zealand's early colonial history, so many settlers died while trying to cross the rivers that drowning was called "the New Zealand death".
People have drowned in as little as of water while lying face down.
Death can occur due to complications following an initial drowning. Inhaled fluid can act as an irritant inside the lungs. Even small quantities can cause the extrusion of liquid into the lungs over the following hours; this reduces the ability to exchange the air and can lead to a person "drowning in their own body fluid". Vomit and certain poisonous vapors or gases can have a similar effect. The reaction can take place up to 72 hours after the initial incident and may lead to a serious injury or death.

Risk factors

Many behavioral and physical factors are related to drowning:
  • Drowning is the most common cause of death for people with seizure disorders, largely in bathtubs. Epileptics are more likely to die due to accidents such as drowning. However, this risk is especially elevated in low and middle-income countries compared to high-income countries.
  • The use of alcohol increases the risk of drowning across developed and developing nations. Alcohol is involved in approximately 50% of fatal drownings, and 35% of non-fatal drownings.
  • Inability to swim can lead to drowning. Participation in formal swimming lessons can reduce this risk. The optimal age to start the lessons is childhood, between one and four years of age.
  • Feeling overly tired reduces swimming performance. This exhaustion can be aggravated by anxious movements motivated by fear during or in anticipation of drowning. An overconfident appraisal of one's own physical capabilities can lead to "swimming out too far" and exhaustion before returning to solid footing.
  • Free access to water can be hazardous, especially to young children. Barriers can prevent young children from gaining access to the water.
  • Ineffective supervision, since drowning can occur anywhere there is water, even in the presence of lifeguards.
  • Risk can vary with location depending on age. Children between one and four more commonly drown in home swimming pools than elsewhere. Drownings in natural water settings increase with age. More than half of drownings occurring among those fifteen years and older occurred in natural water environments.
  • Familial or genetic history of sudden cardiac arrest or sudden cardiac death can predispose children to drown. Extensive genetic testing and/or consultation with a cardiologist should be done when there is a high suspicion of familial history and/or clinical evidence of sudden cardiac arrest or sudden cardiac death.
  • Individuals with undetected primary cardiac arrhythmias, as cold water immersion or aquatic exercise can induce these arrhythmias to occur.
Population groups at risk in the US are the old and the young.
  • Youth: drowning rates are highest for children under five years of age and people fifteen to twenty-four years of age.
  • Minorities: the fatal unintentional drowning rate for African Americans above the age of 29 between 1999 and 2010 was statistically significantly higher than that of white people above the age of 29. The fatal drowning rate of African American children of ages from five to fourteen is almost three times that of white children in the same age range and 5.5 times higher in swimming pools. These disparities might be associated with a lack of basic swimming education in some minority populations.

    Freediving

Some additional causes of drowning can also happen during freediving activities:
  • Ascent blackout, also called deep water blackout, is caused by hypoxia during ascent from depth. 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 occurs when arriving near the surface as the pressure approaches normal atmospheric pressure.
  • Shallow water blackout caused by hyperventilation prior to swimming or diving. The primary urge to breathe is triggered by rising carbon dioxide levels in the bloodstream. The body detects levels accurately and relies on this to control breathing. Hyperventilation reduces the carbon dioxide content of the blood but leaves the diver susceptible to a sudden loss of consciousness without warning from hypoxia. There is no bodily sensation that warns a diver of an impending blackout, and people become unconscious and drown quietly without alerting anyone to the fact that there is a problem. They are typically found at the bottom.

    Pathophysiology

Drowning is split into four stages:
  1. Breath-hold under voluntary control until the urge to breathe due to hypercapnia becomes overwhelming
  2. Fluid is swallowed and/or aspirated into the airways
  3. Cerebral anoxia stops breathing and aspiration
  4. Cerebral injury due to anoxia becomes irreversible
People who do not know how to swim can struggle on the surface of the water for only 20 to 60 seconds before being submerged. In the early stages of drowning, a person holds their breath to prevent water from entering their lungs. 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. If the process is not interrupted, loss of consciousness due to hypoxia is followed by cardiac arrest.

Oxygen deprivation

A conscious person will hold their breath and will try to access air, often resulting in panic, including rapid body movement. This uses up more oxygen in the bloodstream and reduces the time until unconsciousness. The person can voluntarily hold their breath for some time, but the breathing reflex will increase until the person 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 an 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 their breath. This typically occurs at an arterial partial pressure of carbon dioxide of 55 mm Hg but may differ significantly between people.
When submerged into cold water, breath-holding time is significantly shorter than that in air due to the cold shock response. The breath-hold breakpoint 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.
Following this, a blackout may occur before the diver feels an urgent need to breathe. This can occur at any depth and is common in distance breath-hold divers in swimming pools. Both deep and distance free divers often use hyperventilation 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.
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. 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 the lungs during autopsy does not necessarily mean there was no water at the time of drowning, as small amounts of freshwater are absorbed into the bloodstream. Hypercapnia and hypoxia both contribute to laryngeal relaxation, after which the airway is 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.
The hypoxemia and acidosis caused by asphyxia in drowning affect various organs. There can be central nervous system damage, cardiac arrhythmia, pulmonary injury, reperfusion injury, and multiple-organ secondary injury with prolonged tissue hypoxia.
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 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 after six minutes from which recovery is generally considered impossible. Hypothermia of the central nervous system may prolong this. In cold temperatures below 6 °C, the brain may be cooled sufficiently to allow for a survival time of more than an hour.
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.