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  • Drowning and near drowning are most common in young males; drugs and alcohol are frequently associated with such events.

  • Underwater immersion is associated with increases in central blood volume and cardiac output, decreases in thoracic gas volume, and increases in urine output resulting in dehydration; vagally mediated bradycardia may also occur.

  • Water inhalation (often with particulate matter) during drowning or near drowning may elicit laryngospasm, bronchospasm, surfactant depletion/dysfunction, aspiration of vomitus, and/or lung injury.

  • Hypoxemia may culminate in bradycardia and pulseless electrical activity; global anoxic brain injury and acute tubular necrosis may also ensue.

  • Controlled hypothermia (32°C to 34°C for at least 24 hours) may attenuate brain injury in drowning victims; corticosteroids and osmotic diuretics are not effective.

  • 33 feet depth in seawater (FSW) exerts one atmosphere of pressure; accordingly, at 33 FSW, a diver is at 2 atmospheres of pressure.

  • Barotrauma may occur in any tissue location where gas is trapped in a closed space; the most common events occur in the middle ear, sinuses, and lungs.

  • Pulmonary overpressurization usually occurs with ascent that is too rapid; this can lead to pneumothorax, pneumomediastinum, or arterial gas embolization (AGE); AGE leads to air entry into pulmonary veins and systemic dissemination. Treatment is prompt recompression with hyperbaric oxygen.

  • Decompression sickness is caused by the formation of inert gas bubbles in the tissues after dissolved gas becomes supersaturated by a decrease in the ambient pressure.


Medical illnesses associated with immersion in water and underwater diving are a special interest in Pulmonary and Critical Care Medicine. These illnesses are caused by important pathophysiological mechanisms leading in some cases to serious respiratory problems, including hypoxemia, pneumonia, and acute respiratory distress syndrome (ARDS). Caring for these patients requires specialized knowledge and resources, and the paucity of randomized controlled trials is a problem in both areas. However, the great popularity of water sports, including recreational SCUBA diving, makes familiarity with these activities and their associated medical problems highly important for the specialist in respiratory diseases and critical care medicine.

Aquatic environments are deceptively dangerous, and physical skill, experience, and common sense are needed to enjoy them safely. Too often, swimmers, boaters, or divers ignore signs of danger and find themselves in trouble. Some people have impaired faculties with alcohol or other drugs, or inadvertently encounter an aquatic environment for which they are not prepared, or as for small children, without proper supervision. These mistakes translate to a surprisingly large number of incidents, sometimes with disastrous consequences.


Three quarters of the earth’s surface is covered by water, yet innately, humans cannot swim. Without swimming skills, even brief submersion, sometimes in quite shallow water, can result in drowning. Most tragically, the bulk of near-drowning victims are young; and death by drowning occurs most often in children. These accidents occur with greatest frequency ...

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