It is rare but it is something for parents to be aware of. A person can drown up to 24 hours after ingesting a small amount of water in the lungs. Read more here.

Part of the article follows.
***   ***   ***
“Dr. Daniel Rauch, a pediatrician from New York University Langone Medical Center, told TODAY’s Meredith Vieira that there are warning signs that every parent should be aware of. Johnny Jackson exhibited some of them, but unless a parent knows what to look for, they are easily overlooked or misinterpreted.

The three important signs, he said, are difficulty breathing, extreme tiredness and changes in behavior. All are the result of reduced oxygen flow to the brain.

Johnny had two of those signs — he was very tired when he got home, and he had had the accident in the pool. But like most parents, Cassandra Jackson had no idea this could be related to water in his lungs.

Delayed reaction
Rauch said that the phenomenon of dry drowning is not completely understood. But medical researchers say that in some people, a small amount of inhaled water can have a delayed-reaction effect.

“It can take a while for the process to occur and to set in and cause difficulties,” Rauch said. “Because it is a lung process, difficulty breathing is the first sign that you would be worried about.”

The second sign is extreme fatigue, which isn’t always easy to spot. “It’s very difficult to tell when your child is abnormally tired versus normal tired after a hot day and running around in the pool,” Rauch said. “The job of the lungs is to get oxygen into the blood and your brain needs oxygen to keep working, so when your brain isn’t getting oxygen, it can start doing funny things. One of them is becoming excessively tired, losing consciousness and the inability to be aroused appropriately.”

Finally, there are changes in behavior, Rauch said — another tough call when dealing with very small children, whose moods and behavior can change from one minute to the next.

“Another response of the brain to not getting oxygen is to do different things,” Rauch explained, saying parents should be concerned “if your child’s abnormally cranky, abnormally combative — any dramatic change from their normal pattern.”

He admitted, “It is very difficult to pick this up sometimes.” But spotting the warning signs and getting a suspected victim to an emergency room can save a life, he added.

Victims of dry drowning are treated by having a breathing tube inserted so that oxygen can be supplied under pressure to the lungs. “Then we just wait for the lung to heal itself,” he said.”