Drowning Overview and Physiology


Drowning is the process of experiencing respiratory impairment from submersion/immersion in liquid. Outcomes of drowning may be: death, morbidity, or no morbidity. In other words, a person may die from drowning; be injured in a drowning episode; or escape from drowning through rescue or other means. Drowning is a specific cause of asphyxia, resulting from the immersion of the mouth and nose in liquid - usually water - thus preventing the intake of air. Drowning begins with struggle by victim to stay above water, a period of panic, breath holding, loss of normal breathing pattern and air hunger. Patient outcomes are affected by several factors such as a length of submersion time, a temperature of water, presence of contaminants, freshwater or saltwater microorganisms, first aid treatment and time to a treatment center. Learn more about drowning statistics...

Physiology of drowning

Sudden immersion in cold water and the realisation of danger often causes sharp intakes of breath. As water is taken into the mouth, considerable amounts will be swallowed, reducing buoyancy and compounding the problem.

Initially, water is kept out of the lungs by spasms of the larynx, by the closing the epiglottis, and by repeated swallowing. However, as breathing becomes impossible, hypoxia leads quickly to unconsciousness.

Once consciousness is lost, the larynx relaxes, as does the epiglottis, and water is able to enter the lungs. Drowning may be classified into one of five categories:

  • Near drowning. This occurs if the casualty is rescued before the point of apparent death.
  • Dry drowning. This occurs when water has not entered the lungs.
  • Fresh water drowning. This occurs when ‘fresh’ (not salty) water has entered the lungs. The water interferes with the normal mechanism for exchange of gases in the alveoli. The water also upsets the pH value of the blood as it is rapidly absorbed through the walls of the alveoli and from the digestive system. This in turn can lead to imminent cardiac arrest.
  • Salt water drowning. This occurs when salt water has entered the lungs. The presence of salt in the alveoli draws water from the blood increasing the amount of fluid in the lungs, and increasing the viscosity of the blood. This in turn reduces the heart rate and effectiveness of the circulation, and may lead to cardiac arrest within eight to twelve minutes of rescue.
  • Secondary drowning. This occurs as a result of water having entered the body. Water in the stomach is absorbed into the bloodstream, disturbing the pH balance of the blood. This may lead to death up to 72 hours after rescue. Salt water in the lungs can lead to pulmonary oedema (or shocked lung syndrome) many hours after immersion.

Additional factors

Drowning is rarely straightforward - other factors may be involved.

Hypothermia. Immersion for any length of time in cold water may well reduce body temperature to the point of hypothermia.

Mammalian diving reflex. This reflex (which is little understood) can allow complete recovery of apparently dead drowning victims - particularly the young - who have been submerged for 30 minutes or even longer.

It occurs on sudden immersion into icy water, face first. The body systems, particularly respiratory, circulatory, and nervous, enter a condition of almost total shutdown, giving a condition of ‘suspended animation’ and apparent death.

Prolonged immersion collapse. This can occur following rescue of someone who has been immersed in the water for a considerable times, particularly if they have worn a life jacket, which kept them in an ‘upright’ attitude. Whilst in the upright position, the water exerts pressure and a massaging effect on the legs. This assists the flow of venous blood from the lower areas of the body. On rescue, if the casualty is not laid in a horizontal position, the loss of the water pressure, together with the effects of gravity, can lead to fainting or even sudden death, through pooling of blood in the lower areas.

Near Drowning

Near drowning occurs if the casualty is rescued before the point of apparent death. “Wet” near drowning is an aspiration of fluid, “dry” near drowning – a period of asphyxia secondary to laryngospasm into lungs. Duration of submersion, amount of fluid aspirated and severity of hypoxia are among the main factors affecting the outcome. Other factors affecting the incident outcome are:

  • Gram negative bacteria in drowning victims more virulent can cause immediate lethal sepsis or infections months after incident
  • Fungus: incubation time 1-4 weeks to 6 months, often resistant
  • Strep or staph which can also be present

Causes of Hypoxemia include:

  • Decreased lung compliance
  • Damage to surfactant
  • Reflex inspiratory effort
  • Intrapulmonary shunting
  • Ventilation perfusion mismatching

Pulmonary Effects of Near Drowning

Pulmonary insufficiency can develop insiduously or rapidly and also...

  • Alveoli become unstable
  • Complete/partial alveolar collapse
  • Loss of ventilation resulting in intrapulmonary shunting & hypoxemia
  • CXR / CT: vary from normal to localized, perhilar, or diffuse pulmonary edema
  • Surface tension properties of surfactant affected
  • Surfactant “washed out”
  • Water in alveoli prevents production of new surfactant and damages type 2 pneumocytes
  • Loss of surfactant function

Increased airway resistance secondary to:

  • Plugging of airway wiith debris
  • Release of inflamatory mediators that result on vasoconstriction
  • May impair gas exchange

Combination of above factors as well as a damage to alveolar capillaries & interstitium can lead to ARDS. ARDS develops within 48 hours in approximately 40% of neardrowning victims. Hallmarks of ARDS include severe hypoxemia, decreased lung compliance and bilateral infiltrates on CXR. Recovery occurs in 80% of cases and the most effective treatment is reversal of hypoxemia with mechanical ventilation support.

Neurologic Effects: Hypoxemia and ischemia may cause neuronal damage producing cerebral edema and elevation in ICP.

Cardiovascular Effects: arrhythmia is secondary to hypothermia & hypoxemia and sinus bradycardia and atrial fibrillation are more common than ventricular fibrillation or asystole.

Renal Effects: failure is rarely occurs but if it does, usualy it's due to an acute tubular necrosis or other factors such as shock, hypoxemia, hemoglobinuria or myoglobinuria.

Learn more about drowning statistics...