Etiology and Pathogenesis

Hypoxemia is the driving force of the process of drowning, initially caused by apnea and then caused by aspiration. After submersion, drowning victims typically hold their breath and struggle. Small amounts of water are aspirated, and involuntary laryngospasm and hypoxia ensue. With continued hypoxia, the vocal cords relax, and larger amounts of water are aspirated. Even greater amounts of water are swallowed than aspirated, and vomiting is common. The cascade of pulmonary damage from drowning can occur with aspiration of as little as 1 to 3 mL/kg of water.

The effects of aspiration and continued submersion are many (Figure 6-2). Within the alveoli, water prevents diffusion of oxygen across the capillary/alveolar membrane. The capillary endothelium becomes increasingly permeable, resulting in pulmonary edema. Aspiration of gastric contents contributes to lung injury. As pulmonary edema and intrapulmonary shunt progress, hypoxia, hypercarbia, and acidosis ensue. These metabolic disturbances decrease myocardial contractility, increase systemic vascular resistance, and contribute to arrhythmias. If submersion continues long enough, drowning will progress to cardiac arrest. Clinically, there is little difference between fresh and salt-water drownings; however, there are some putative pathophysiologic differences. Whereas fresh water is particularly destructive to surfactant, salt water causes osmotic forces to draw additional fluid into the alveoli. Electrolyte disturbances are rare; however, ingestion of large amounts of fresh water can cause hyponatremia, and salt water ingestion can cause hypernatremia. Ingestion of large quantities of fresh water in the setting of hypoxemia may lead to hemolysis, although this is also a rare event.

Figure 6-2 Pathophysiology of drowning.

Hypothermia is often present and causes peripheral vasoconstriction, which preserves blood flow to the central organs. Increased core blood flow triggers central volume receptors to perceive greater blood volume and thus produce less antidiuretic hormone, resulting in diuresis and volume depletion.

Clinical Presentation

The duration of submersion and hypoxia will determine the clinical presentation and outcome in drowning victims. Submersions less than 5 minutes are associated with intact survival, but submersions more than 25 minutes have almost universally poor outcomes. Many victims are rescued from the water in cardiac arrest, and immediate, effective cardiopulmonary resuscitation (CPR) can improve survival rates and neurologic outcome. After pulses are restored, signs of shock may be present, including hypotension, diminished peripheral pulses, altered level of consciousness, acidosis, and decreased urine output. Patients may appear cold, cyanotic, and unresponsive. More mildly affected patients may have isolated pulmonary findings such as wheezes, crackles, cough, or hypoxia. Neurologic findings range from an alert child to any amount of central nervous system compromise, including coma with flexor or extensor posturing.

Many studies have evaluated factors associated with good outcomes, and better prediction is possible with parameters measured later in the hospital course than at initial presentation or in the field. There have been reports of pediatric survivors with good outcomes despite ominous predictors such as submersion over 1 hour. Thus, all patients should receive aggressive initial resuscitation in the field and emergency department (ED), regardless of circumstances surrounding the drowning. After initial resuscitation, failure to exhibit reflexes or response to external stimuli within the first 24 hours of care predicts a poor neurologic outcome.

Unusually good outcomes have occurred in cold-water drownings in children. It is believed that sudden exposure of the face to icy water triggers a protective “diving reflex” that causes apnea, bradycardia, and vasoconstriction. The resultant decreased metabolic demands seem to improve the chances of neurologic recovery compared with warm-water drownings of similar duration. An alternative theory is that rapid cerebral cooling leads to decreased cerebral metabolic demand and is responsible for these outcomes. Ultimately, these good outcomes are relatively rare, and the reasons for them remain unclear.

It is important to consider potential coexistent injuries and risk factors for drowning. Drowning may be associated with other trauma, including head injury, blunt abdominal trauma, and spinal injury (Figure 6-3). Seizures, cardiac arrhythmias, hypoglycemia, and intoxication can all contribute to a drowning event.

Figure 6-3 Injury to the cervical spine during drowning.