A few years ago, I took care of a child who changed the way I practice pediatrics. His case underscored the need to ask one key question. "Does your child snore?"

The child was 3, with no real medical problems, except that he was overweight. His mother brought him into my office concerned about his persistent cough and mentioned that he was also short of breath more often when he ran around.

To help him sleep, the woman added, she had to put two pillows under his head. A physical exam showed fluid in the lower parts of his lungs.

If this were an older adult, I would have thought he was in heart failure. But a 3-year-old? Unfathomable.

We sent him to the hospital, where an ultrasound indeed showed heart failure. He was admitted to the intensive care unit and put on medications to help his heart work better. Then he fell asleep.

In 2002, the American Academy of Pediatrics published its first practice guidelines to diagnose and manage obstructive sleep apnea syndrome in children. Since then, much research has been done. The guideline was updated this year. One recommendation that hasn't changed, but that is often ignored, is for clinicians to ask all parents whether their children snore because most parents do not mention this concern during routine visits.

"Don't ask, won't tell" can miss many a diagnosis.

Sleep apnea occurs when the airway is blocked, disrupting normal breathing and sleep. The prevalence of sleep apnea is about 3 percent and is rising, mostly due to the epidemic of childhood obesity, which afflicts more than 20 percent of our city's children.

The problems linked to sleep apnea include bedwetting, behavioral problems, poor weight gain, bad school performance, high blood pressure, uncontrolled asthma, attention problems, mouth breathing, heart strain, and morning headaches. Sleeping with the neck extended or in a seated position may be a clue that children are trying to adjust their bodies to breathe better at night, usually without success.

Obesity is one risk factor for sleep apnea in children. Others are tonsil and adenoidal enlargement, facial structural problems, genetics, and poverty. Also, African American children, regardless of weight, are 3.5 times more likely to have sleep apnea.

So here we are in Philadelphia. A population of 346,000 children, 40 percent in poverty, 44 percent African American. By my calculation, that equates to thousands of exhausted children struggling in school and at home. Thousands deprived of a normal sleep cycle. Thousands undiagnosed.

The causes of sleep apnea vary, but having large adenoids - the tonsilar tissue where the nasal cavity joins the throat - is the most common. This condition develops most often at age 2 to 4. Can you imagine adenoids the size of a ping-pong ball interfering with a child's normal breathing?

The second most common cause is obesity. This can lead to fatty infiltration of the soft tissue around the throat, which can partially block the opening to the lungs, causing the typical snoring, gasping, and cessation of breathing that keeps parents awake at their children's bedside, worrying that each labored breath might be the last.

How do we diagnose sleep apnea in children?

If you are a parent whose child snores or has long pauses in breathing at night, let your doctor know. If you are a day-care worker and hear these sounds, let the parents know.

The gold standard to diagnose sleep apnea is polysomnography, a sleep study.

The study is done in a certified lab where the child sleeps with several monitors that check oxygen and carbon dioxide levels, heart rate, chest-wall movements, and sometimes brain-wave activity. If the sleep study comes back abnormal, it's usually recommended that the adenoids and tonsils be removed.

If a child is morbidly obese or the surgery isn't a success, there are other options, such as a breathing machine at night (continuous positive airway pressure, or CPAP) which is difficult for children to use consistently, or another type of surgery.

What about my 3-year-old patient? Soon after he was stabilized and had fallen asleep in the ICU, the nurses rushed into his room, responding to monitors blaring that his oxygen level had dropped into a dangerous range.

As the nurses clamored by his bedside, another sound emerged amid the monitor alarms: Snoring. The child's mother, quite relaxed, propped his head up on several pillows, waking him from his chaotic sleep. She then turned to the nurses and smiled. "That's what I've been doing each time he does this at night," she said calmly, "just like my husband."

At a follow-up visit a week after his ordeal, the boy's heart was back to normal. I looked into his mouth and stared in wonder at the noticeable absence of tonsilar tissue, which had been removed. "Sleeping better?" I asked. "Much," his mother replied with a grin.

Daniel Taylor is an associate professor at Drexel University College of Medicine and a pediatrician with St. Christopher's Hospital for Children. His e-mail address is Daniel.Taylor@DrexelMed.edu.