Drowning is defined as respiratory impairment resulting from submersion or immersion in a liquid medium. This event initiates physiological responses that rapidly compromise the body’s ability to exchange gases, primarily impacting the lungs. The physical and chemical changes within the respiratory system determine the outcome and severity of the injury. Understanding these breakdowns reveals how quickly a life-threatening situation develops once water enters the airway.
The Body’s Initial Protective Response
When water contacts the upper airway, the body triggers an involuntary defensive reflex called laryngospasm. This mechanism involves the tight closure of the vocal cords in the larynx. The closure effectively seals off the trachea, preventing liquid from traveling into the lower respiratory tract.
This protective spasm prevents initial water aspiration into the lungs but is not permanent, typically lasting around one minute. As the body depletes its oxygen stores, the need to breathe overcomes the muscle contraction, and the laryngospasm fatigues.
Once the vocal cords relax, the overwhelming drive to inhale results in the aspiration of water into the lungs. This aspiration marks the transition to mechanical and chemical disruption of the lung structures and leads to extensive damage within the pulmonary system.
Structural Damage from Fluid Aspiration
When water is aspirated into the lungs, it quickly reaches the alveoli, the tiny air sacs responsible for gas exchange. The presence of foreign fluid initiates physical and chemical injuries. A primary consequence is the disruption of surfactant, a fatty lipoprotein substance.
Surfactant normally coats the inner surface of the alveoli, reducing surface tension and keeping the air sacs open. Its destruction causes the alveolar walls to stick together and collapse, a condition known as atelectasis. This collapse severely reduces the surface area available for oxygen to enter the bloodstream.
Water in the alveoli also damages the surrounding alveolar-capillary membrane, the thin barrier separating air from blood. This damage increases the membrane’s permeability, causing fluid to leak from blood vessels into the air sacs. This influx of fluid is called pulmonary edema, which further floods the lungs, creating a foam-like mixture that obstructs the airways and impedes ventilation. Regardless of whether the fluid is fresh or salt water, the resulting physical damage is similar, manifesting as acute lung injury and a severe mismatch between ventilation and blood flow. The lungs become stiff and less compliant, making it difficult to breathe, even if the person is rescued.
Systemic Failure Due to Oxygen Deprivation
The failure of the lungs to function correctly impacts the entire body by halting gas exchange. With the alveoli compromised by collapse and edema, oxygen cannot be transferred effectively into the blood, leading to a rapid drop in blood oxygen saturation, or hypoxemia. Simultaneously, the body cannot expel carbon dioxide, causing it to build up in the bloodstream, a condition called hypercapnia.
The resulting lack of oxygen supply to the tissues is termed hypoxia, which drives systemic failure. The central nervous system, particularly the brain, is highly sensitive to oxygen deprivation and can sustain irreversible damage within minutes. Hypoxia can also trigger cerebral edema, an accumulation of fluid in the brain, further elevating the neurological injury.
The heart is also affected by the lack of oxygen and the resulting metabolic acidosis from the buildup of waste products. This combination of factors can lead to cardiac rhythm disturbances, including a slow heart rate (bradycardia), eventually progressing to cardiac arrest. The outcome of the drowning process is often determined by the extent and duration of the cerebral hypoxia.
Post-Rescue Complications
Even after a person is rescued, damage to the lungs can lead to complications hours or days later. This delayed presentation occurs when a small amount of aspirated fluid causes ongoing inflammation and irritation of the alveolar lining. The inflammation leads to a progressive fluid buildup in the lungs, a delayed form of pulmonary edema.
This delayed condition, sometimes referred to as secondary drowning, can result in increasing difficulty breathing, persistent coughing, and fatigue as the lungs become less efficient. Any victim who has experienced a submersion event should be monitored closely for these respiratory symptoms for up to 72 hours.
Aspiration pneumonia is a serious complication that can develop, particularly if the water inhaled contained bacteria, chemicals, or particulate matter. The introduction of contaminants causes a secondary infection in the damaged lung tissue, requiring immediate medical treatment. Both delayed edema and pneumonia underscore the need for medical evaluation following any water aspiration event.