Children exposed to secondhand smoke often have levels of carbon monoxide in their blood that are similar to those of adult smokers, and

frequently higher levels than adults exposed to secondhand smoke, a new study found.

The study, to be presented at the American Society of Anesthesiologists annual meeting that concludes Oct. 22 in Orlando, Fla., said the younger the child, the greater the potential for exposure.

"The physiology of children -- especially the youngest -- is different from that of adults," Dr. Branden E. Yee, of the anesthesiology department at Tufts Medical Center in Boston, said in a news release issued by the society. "Children breathe in a greater amount of air per body weight compared to adults."

The study measured levels of carboxyhemoglobin, which is formed when carbon monoxide binds to the blood, in 200 children between the ages of 1 and 12. The exact ramifications of high levels of carboxyhemoglobin are not entirely known, but long-term, low-level exposure includes changes in heart and lung tissue as it hampers delivery of oxygen to body tissue.

While household and environmental factors such as stoves, heaters and automobiles are potential sources of carbon monoxide exposure, secondhand cigarette smoke is often the most likely source of elevated carboxyhemoglobin, the researchers said.

Yee said educating parents about the need to change their smoking habits, especially around children, is vital.

"Personalized education coupled with the act of physically showing a parent the carboxyhemoglobin measurement in his or her child's blood may provide a graphic and concrete message to that parent," he said.