Anatomic Alterations of the Lungs

Drowning is defined as suffocation and death as a result of submersion in liquid. Drowning may be classified further as near drowning, dry drowning, and wet drowning. Near drowning refers to the situation in which a victim survives a liquid submersion, at least temporarily. In dry drowning the glottis spasms and prevents water from passing into the lungs. The lungs of dry drowning victims are usually normal.

In wet drowning the glottis relaxes and allows water to flood the tracheobronchial tree and alveoli. When fluid initially is inhaled, the bronchi constrict in response to a parasympathetic-mediated reflex. As fluid enters the alveoli, the pathophysiologic processes responsible for noncardiogenic pulmonary edema begin—that is, fluid from the pulmonary capillaries moves into the perivascular spaces, peribronchial spaces, alveoli, bronchioles, and bronchi. As a consequence of this fluid movement, the alveolar walls and interstitial spaces swell, pulmonary surfactant concentration decreases, and the alveolar surface tension increases.

As this condition intensifies, the alveoli shrink and atelectasis develops. Excess fluid in the interstitial spaces causes the lymphatic vessels to dilate and the lymph flow to increase. In severe cases the fluid that accumulates in the tracheobronchial tree is churned into a frothy, white (sometimes blood-tinged) sputum as a result of air moving into and out of the lungs (generally by means of mechanical ventilation).

Finally, if the victim was submerged in unclean water (e.g., swamp, pond, sewage, or mud), a number of pathogens (e.g., Pseudomonas) and solid material may be aspirated. When this happens, pneumonia may occur, and in severe cases, acute respiratory distress syndrome (ARDS) may develop. Although the theory has been controversial in the past, it is now believed that the major pathologic changes of the lungs are essentially the same in fresh water and sea water wet drownings; both result in a reduction in pulmonary surfactant, alveolar injury, atelectasis, and pulmonary edema (see Figure 40-1).

The major pulmonary pathologic and structural changes associated with wet drowning are as follows:

Etiology and Epidemiology

Each year 6000 to 8000 people drown in the United States. Drowning is the third leading cause of accidental death in the United States. Drowning is the second leading cause of accidental death in people 5 to 44 years of age. About 15% of children experience near drowning by middle-school age. Drowning is most common in teenagers and in children younger than 4 years of age. More than 40% of drownings are in the under-4 age group. Swimming pools with poor adult supervision are the most common sites of drownings. Up to 33% of adults have experienced near drowning at some time. Alcohol use is present in about 50% of adult drownings. African-American children drown at a rate of 4.5 per 100,000 annually, usually in freshwater lakes and ponds. Caucasian children drown at a rate of 2.5 per 100,000 annually, usually in home pools.

Box 40-1 summarizes the general sequence of events that occurs in drowning or near drowning. Victims submerged in cold water generally demonstrate a much higher survival rate than victims submerged in warm water. Table 40-1 lists favorable prognostic factors in cold-water near drowning.