Drowning refers to the clinical state of death caused by asphyxial hypoxia resulting from the body being submerged in water or another liquid, leading to reflexive laryngospasm and/or respiratory impairment. Immersion syndrome describes sudden cardiac arrest or sudden death caused by immersion in water that is at least 5°C below body temperature. Post-immersion syndrome refers to respiratory distress that develops after a period of recovery following submersion due to alveolar capillary endothelial injury and leakage, which triggers pulmonary inflammatory responses and inactivation or reduction of alveolar surfactant. This condition is classified as a type of acute respiratory distress syndrome (ARDS). Drowning predominantly occurs in the summer, with higher incidences in coastal countries and regions. According to World Health Organization (WHO) data, approximately 236,000 people die from drowning annually worldwide, with over half being under the age of 30 as of 2019.
Etiology
Drowning is commonly observed in individuals involved in water sports activities such as swimming or boating accidents, divers experiencing head, neck, or spinal cord trauma, or divers who lose consciousness due to events like epilepsy, heart disease, arrhythmias, or hypoglycemia. Factors such as alcohol consumption or the use of medications affecting brain function prior to entering the water, along with prolonged physical activity in the water resulting in exhaustion, also increase risk. Drowning may also occur during natural disasters such as floods, traffic incidents involving water, or intentional acts such as suicide by submersion.
Pathogenesis
Within seconds of submersion, individuals instinctively hold their breath for less than one minute, activating the diving reflex characterized by apnea, bradycardia, and severe peripheral vasoconstriction. This reflex prioritizes blood supply to the heart and brain. When breath-holding ceases, involuntary inhalation occurs, allowing water to enter the airways, which triggers reflexive coughing and occasionally laryngospasm. Increased airway fluid results in severe respiratory impairment, leading to hypoxia, hypercapnia, and metabolic acidosis.
As brain hypoxia progresses, laryngospasm disappears, causing asphyxia and unconsciousness. This is followed by tachycardia, bradycardia, pulseless electrical activity, and eventually cardiac arrest. The drowning process, from submersion to cardiac arrest, typically spans from a few seconds to several minutes.
Drowning is classified based on the type of immersion medium into freshwater drowning and saltwater drowning.
Freshwater Drowning
Freshwater accounts for approximately 90% of drowning incidents, with about 50% occurring in swimming pools. Freshwater, derived from sources such as rivers, lakes, or ponds, has lower osmotic pressure compared to plasma and other bodily fluids. Freshwater absorbed into the body through the respiratory or gastrointestinal tract rapidly enters the bloodstream, increasing blood volume. In severe cases, this can lead to hemolysis, hyperkalemia, and hemoglobinuria. The most significant pathological change associated with freshwater inhalation is pulmonary injury. Damage includes inactivation of alveolar surfactant, reduced lung compliance, alveolar collapse and shrinkage, destruction of respiratory membranes, and a marked decrease in alveolar volume, resulting in ventilation-perfusion mismatch. Even with rapid resuscitation, acute lung injury remains unabated, leading to widespread pulmonary edema or small atelectasis. Additionally, fluid within the alveoli interferes with normal gas exchange, impairing oxygenation.
Saltwater Drowning
Saltwater contains sodium levels that are more than three times higher than plasma. Inhaled saltwater remains in the alveoli for a longer duration compared to freshwater and promotes the movement of water from the bloodstream into the alveolar cavity, causing pulmonary edema, intrapulmonary shunting, reduced gas exchange, and the development of hypoxemia. Saltwater also damages alveolar epithelial cells and pulmonary capillary endothelial cells, increasing permeability and further contributing to the progression of pulmonary edema. Despite differences in osmotic gradients between freshwater and saltwater, the degree of pulmonary injury in both types of drowning is comparable. Both reduce pulmonary compliance, cause pulmonary edema, intrapulmonary shunting, hypoxemia, and mixed acidosis.
Inhalation of 1–3 ml/kg of freshwater or saltwater is sufficient to disrupt alveolar surfactant, causing alveolar collapse, atelectasis, noncardiogenic pulmonary edema, intrapulmonary shunting, and ventilation-perfusion mismatch. Differences exist between freshwater and saltwater drowning in the mechanisms of electrolyte imbalance, hemolysis, and fluid compartmental shifts. The primary cause of sudden death in most drowning victims is severe arrhythmia. Rapid death caused by immersion in ice water is usually attributed to bradycardia or cardiac arrest. Sudden exposure to cold water can stimulate the vagus nerve, prolong the QT interval, and cause massive catecholamine release, triggering ventricular fibrillation, cardiac arrest, and loss of consciousness. The prognosis for immersion syndrome worsens with larger temperature differences between the body and the immersion medium. Pre-wetting the face and head with cold water prior to submersion may provide some preventive effects.
Hypothermia resulting from drowning can sometimes extend the window for resuscitation and improve survival chances by reducing brain oxygen consumption and delaying cellular hypoxia and ATP depletion. As body temperature drops from 37°C to 20°C, each 1°C reduction decreases brain oxygen consumption by approximately 5%. Severe brain hypoxia may contribute to the development of neurogenic pulmonary edema.
Pathology
Autopsy findings reveal that most drowning victims have an inspiratory water volume of less than 4 ml/kg. The lungs of drowning victims are often characterized by increased water content, significantly increased weight, varying degrees of hemorrhage, edema, and alveolar wall rupture. Approximately 70% of drowning victims exhibit aspirated vomitus, sediments, or aquatic vegetation in their airways. Secondary drowning patients may demonstrate sloughing of alveolar epithelial cells, hemorrhage, hyaline membrane formation, and acute inflammatory exudation. Additionally, acute tubular necrosis lesions may be observed.
Clinical Manifestations
In cases of drowning, loss of consciousness, cessation of breathing, or disappearance of major arterial pulsation commonly indicates a state of clinical death. The clinical presentations of near-drowning patients vary significantly among individuals and are influenced by factors such as the duration of submersion, the volume and type of inhaled medium, and the severity of organ injury.
Symptoms
Patients who have experienced near-drowning may present with headache or visual disturbances, severe coughing, chest pain, difficulty breathing, and the production of pink, frothy sputum. Individuals who have inhaled seawater often experience pronounced thirst and may develop chills and fever within the first few hours.
Signs
Drowning victims may present with foam or debris in the mouth and nasal cavities, cyanosis of the skin, facial swelling, conjunctival congestion, and increased muscle tone. Altered mental and neurological states, including restlessness, convulsions, lethargy, or coma, may also occur. Breathing may be shallow, rapid, or absent, with the presence of dry or wet rales detected in the lungs. Cardiac irregularities, weak heart sounds, or complete cardiac arrest may be observed. Abdominal distension and cold extremities are frequently noted.
When diagnosing drowning, the duration of submersion and the presence of head or intracranial injuries require attention. Diving or underwater drowning incidents are sometimes accompanied by head or cervical spine trauma.
Laboratory and Other Examinations
Blood and Urine Tests
Peripheral blood may show a mild increase in white blood cells. In cases of freshwater drowning, elevated potassium levels and the presence of free hemoglobin in blood and urine may be detected. In seawater drowning, hypernatremia or hyperchloremia is possible. Severe cases may exhibit laboratory evidence of disseminated intravascular coagulation (DIC).
Electrocardiography (ECG)
ECG findings may indicate sinus tachycardia, nonspecific ST-segment and T-wave changes, ventricular arrhythmias, or complete cardiac conduction block.
Arterial Blood Gas Analysis
Severe mixed acidosis occurs in approximately 75% of patients, with all individuals presenting with varying degrees of hypoxemia.
X-ray Imaging
Pulmonary infiltration and pulmonary edema may develop within a few hours after drowning, with chest X-rays revealing patchy infiltrates. Early chest X-rays can sometimes underestimate the severity of lung injury. Recovery or further deterioration may occur 12 to 24 hours after hospitalization. Cervical spine X-rays are required when cervical spine injury is suspected. Early CT scans of the brain usually provide limited benefit, whereas MRI conducted 3 to 4 days after drowning is more suitable for predicting the patient’s neurological prognosis.
Treatment
Prehospital Emergency Care
On-site Emergency Measures
The drowning victim is removed from the water as quickly as possible. The prone position with the head lowered is used to facilitate drainage. Oral, nasal secretions, debris, and foreign materials are promptly cleared from the airways. Back-patting may assist in expelling fluid from the airways to ensure they remain unobstructed. For patients with suspected airway obstruction by foreign objects, the Heimlich maneuver can be applied to relieve the obstruction.
Cardiopulmonary Resuscitation (CPR)
For victims experiencing cardiac and respiratory arrest, CPR, endotracheal intubation, and oxygen delivery are initiated immediately on-site. Approximately 5% of drowning victims rescued by lifeguards require CPR, while about 30% of those rescued by bystanders require such intervention. Only those with professional training are qualified to administer CPR in water. Aspiration risk should be monitored during resuscitation, and CPR should not be interrupted during the transfer of the patient.
In-Hospital Management
Oxygen Therapy
Patients receive high-concentration oxygen or hyperbaric oxygen therapy, and mechanical ventilation is employed when necessary based on the severity of the situation. Arterial blood gas levels are monitored in all drowning cases. Conscious individuals may undergo continuous positive airway pressure (CPAP) via a face mask or nasal mask. Patients with severe or progressive respiratory distress, unprotected airway reflexes, head or chest injuries, or those with arterial carbon dioxide (PaCO2) exceeding 50mmHg are intubated and placed on mechanical ventilation. Patients with oxygen saturation below 90% or arterial oxygen pressure (PaO2) below 60mmHg following high-flow oxygen therapy require positive-pressure ventilation.
Rewarming
Hypothermic patients undergo internal or external rewarming to restore core body temperature to at least 30–35°C.
Neurological Resuscitation
For patients with elevated intracranial pressure or in a comatose state, ventilatory support is adjusted to maintain PaCO2 levels between 25–30mmHg. Intravenous infusion of mannitol is used to reduce intracranial pressure and mitigate cerebral edema. Naloxone may be administered empirically.
Antibiotic Therapy
Antibiotics are provided to individuals drowning in contaminated water, displaying infection signs, or presenting with sepsis.
Management of Complications
Appropriate treatment is provided for complications such as seizures, hypotension, cardiac arrhythmias, pulmonary edema, acute respiratory distress syndrome (ARDS), stress ulcers with bleeding, and metabolic or electrolyte abnormalities.
Prognosis
The severity of lung damage and brain hypoxia caused by drowning depends on the volume of medium inhaled and the duration of submersion, rather than whether freshwater or seawater is involved. Patients who regain consciousness within an hour of treatment generally have favorable outcomes. A shorter time from rescue to the recovery of spontaneous breathing is associated with a better prognosis. Approximately 20% of survivors of drowning experience varying degrees of neurological impairments, including central quadriplegia, extrapyramidal syndromes, and peripheral nerve or muscle damage. Occasionally, individuals with prolonged coma, hemodynamic instability, and dilated pupils can still recover full neurological function. In recent years, the mortality rate due to drowning has significantly decreased.
Prevention
Regular and rigorous health examinations are conducted for individuals engaged in water-related occupations.
Individuals with chronic or underlying health conditions avoid participating in aquatic activities.
Alcohol consumption is avoided before engaging in water-based tasks to prevent impaired judgment and self-protective abilities.
Education and training on swimming, water safety, self-rescue, and mutual aid techniques are recommended. Life-saving equipment should be readily available during water-related activities.
Swimming is avoided in complex natural water bodies, and diving or snorkeling in shallow waters is avoided.
Adequate warm-up exercises are completed before entering the water, and swimming in low-temperature water is avoided.