Etiology

Inability to keep the airway above the surface of the water precipitates a drowning episode. This may occur due to medical illness, lack of physical ability, or inability to cope with environmental conditions (e.g., temperature, waves, currents, or depth). Falls, boating or motor vehicle accidents, and medical comorbidities (seizures, stroke, intoxication, or cardiac disease) may cause physical or mental incapacitation, leading to drowning. Severity and complications of drowning are related to hypoxemia induced by asphyxiation from submersion, and lung injury from aspiration.

Pathophysiology

The drowning process, from submersion or immersion to cardiac arrest, usually occurs in seconds to a few minutes. In unusual situations, such as a fall into freezing water, this process can last up to 1 hour.[12]

In less than 2% of cases, laryngospasm may be present when the person begins to inhale water.[13][14]​ Airway obstruction results in impaired oxygenation and ventilation, leading to apnea, hypoxemia, and loss of consciousness. Hypoxic cardiac arrest generally occurs after a period of bradycardia and pulseless electrical activity, and not by means of ventricular fibrillation.[15][16]​ In most instances of drowning-related cardiac arrest, the heart tissue is relatively healthy and ceases perfusion due to hypoxic insult.[17][18]

The clinical picture is determined by the reactivity of the airways and the amount of water that has been aspirated, but not by the type of water (salt or fresh). Aspiration of water leads to surfactant destruction and wash-out in the alveoli, and to hypoxia. The effect of the osmotic gradient on the alveolar-capillary membrane can disrupt the integrity of the membrane, increase its permeability, and exacerbate fluid, plasma, and electrolyte shifts.[15] Regional or generalized pulmonary edema result, which may alter oxygen exchange.[15]​​[17]​​[19] As little as 1 to 3 mL/kg of water aspiration produces profound alterations in pulmonary gas exchange and decreases pulmonary compliance by 10% to 40%.[15] The combined effects of fluid in the lungs, loss of surfactant, and increased capillary-alveolar permeability can result in decreased lung compliance, increased right-to-left shunting in the lungs, atelectasis, and alveolitis.[15]

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