The researchers called on manfufacturers to change the design of infant car seats. (CBC)

Infant car seats save lives in traffic collisions, but they should not be used as a substitute for a crib, say researchers who found mild respiratory problems in healthy newborns placed in the seats.

Infant car seats require infants to be placed in an upright position compared with sleeping flat in a crib. It's thought that the seats can compress the chest wall of newborns and reduce the amount of oxygen they are able to breathe.

"In healthy term newborns, significant [oxygen] desaturations were observed in both car beds and car seats as compared with hospital cribs, Dr. Bernard Kinane, chief of pulmonary pediatrics at Massachusetts General Hospital, in Boston, and his colleagues concluded in Monday's issue of the journal Pediatrics.

"The use of these devices should, therefore, be restricted to protection from injury and death in traffic accidents, and they should never serve as a replacement for a crib. In addition, further modifications of car safety devices are clearly needed to minimize the respiratory compromise that had been consistently documented in current models."

It's known that premature infants can experience periods of low oxygen while they are in car seats. Specially designed car seats known as car beds can help prevent the low-oxygen events for preemies or newborns at risk of respiratory problems.

In the study, researchers found cars seats and car bed resulted in mild respiratory compromise in about 20 per cent of newborns.

The team looked at 200 healthy newborns who were placed sequentially for 30 minutes in a hospital crib, 60 minutes in a car bed, and 60 minutes in a car seat.

Average oxygen saturation levels were 95.7 per cent in a car seat, 96.3 per cent in a car bed and 97.9 per cent in a hospital crib, the researchers found.

The average total time spent with mildly lower oxygen saturation levels also differed significantly for car seats and car beds compared with a hospital crib.

When the experiment was repeated with 50 infants sleeping for two hours, the results were similar.

Check recline angle of car seat

If body positioning in the devices promotes REM (rapid eye movement) sleep then oxygen saturation levels would be reduced, the researchers said. But they did not determine the stage of sleep, which is one of the limitations of the study.

Parents often use car seats, and car beds are often used for many hours at a time for reasons other than travel, which the study's authors discouraged.

Car seats are designed for use in cars only.

At some Canadian hospitals, nurses will check whether a newborn is strapped into the seat properly.

But the way the car seat is positioned in the car itself is also important. Generally, infant car seats should sit at a 45-degree angle to prevent a baby from slumping and closing its airway.

Caregivers are advised to read the owner's manual for the car seat, since each car-seat manufacturer specifies the correct reclining angle for their device. Some fire and emergency officials also offer DVDs to explain the installation process.