Drowning Asphyxia Death

[William Dupere]

Drowningis 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 incident. 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, vomiting, 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 of vomit, or acute respiratory distress syndrome (respiratory failure from lung inflammation).

Drowning is more likely to happen when spending extended periods of time near large bodies of water.[4][6] 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.[6] Common drowning locations include natural and man-made bodies of water, bathtubs, and swimming pools.[3][7]

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.[9] Significant amounts of water usually only enter the lungs later in the process.[4]

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.[10] Sometimes the term "near-drowning" is used in the latter cases. Among children who survive, health problems occur in about 7.5% of cases.[7]

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 (such as with fencing of swimming pools), and exercising appropriate supervision.[6][5] Treatment of victims who are not breathing should begin with opening the airway and providing five breaths of mouth-to-mouth resuscitation.[7] Cardiopulmonary resuscitation (CPR) is recommended for a person whose heart has stopped beating and has been underwater for less than an hour.[7]

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 (rivers, lakes, and a relatively small number of swimming pools); the remaining 10% take place in seawater.[11] Drownings in other fluids are rare and often related to industrial accidents.[12] 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".[13]

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 (pulmonary edema) 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 (as in chemical warfare) 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.[15]

A conscious person 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 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 tries to breathe, even when submerged.[28]

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 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.[29] 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.[30]

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.[32]

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.[33][34]

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.[32]

Aspirated water that reaches the alveoli destroys the pulmonary surfactant, which causes pulmonary edema and decreased lung compliance, compromising oxygenation in affected parts of the lungs. This is associated with metabolic acidosis, 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. The 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).[37] ALI/ARDS can be triggered by pneumonia, sepsis, and water aspiration. These conditions are life-threatening disorders that can result in death if not treated promptly.[37] During drowning, aspirated water enters the lung tissues, causes a reduction in pulmonary surfactant, obstructs ventilation, and triggers a release of inflammatory mediators which results in hypoxia.[37] Specifically, upon reaching the alveoli, hypotonic liquid found in freshwater dilutes pulmonary surfactant, destroying the substance.[38] 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.[38] 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.[37]

Whether a person drowns in freshwater or salt water makes no difference in respiratory management or its outcome.[39] People who drown in freshwater may experience worse hypoxemia early in their treatment; however, this initial difference is short-lived.[39]

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 maximise the time it can stay underwater. The strength of this reflex is greater in colder water and has three principal effects:[40]

The reflex action is automatic and allows both a conscious and an unconscious person to survive longer without oxygen underwater 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 people who are treated with deep hypothermia.[42][43]

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