Passive drowning: People who suddenly sink or have sunk due to a change in their circumstances. Examples include people who drown in an accident due to sudden loss of consciousness or sudden medical condition. 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. Silent drowning: Drowning without a noticeable external display of distress. Dry drowning
Dry drowning is a term that has never had an accepted medical definition, and that is currently medically discredited. Following the 2002 World Congress on Drowning in Amsterdam, a consensus definition of drowning was established: it is the "process of experiencing respiratory impairment from submersion/immersion in liquid." This definition resulted in only three legitimate drowning subsets: fatal drowning, non-fatal drowning with illness/injury, and non-fatal drowning without illness/injury. 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". Such organizations include the International Liaison Committee on Resuscitation, the Wilderness Medical Society, the American Heart Association, the Utstein Style system, the International Lifesaving Federation, the International Conference on Drowning, Starfish Aquatics Institute, the American Red Cross, the Centers for Disease Control and Prevention (CDC), the World Health Organization and the American College of Emergency Physicians.Drowning experts have recognized that the resulting pathophysiology of hypoxemia, acidemia, and eventual death is the same whether water entered the lung or not.
In most people, the laryngospasm relaxes sometime 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. 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. An absence of water in the lungs may be either a dry drowning or indicates a death before submersion.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). 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. 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. Specifically, upon reaching the alveoli, hypotonic liquid found in freshwater dilutes pulmonary surfactant, destroying the substance.