Since the day her newborn daughter left the hospital, Lakshmi Nair has always used her car seat as instructed.
The 30-year-old first-time mother, who also happens to be an anesthesiologist in private practice at Medical City Hospital in Dallas, works on airways for a living. She said that she has never -- not even once -- imagined that the car seat restraining her daughter, Maithili, now 8 months old, was in any way affecting her breathing.
"I've never had a problem with my car seat," said Dr. Nair. "Even when [Maithili] is sleeping in it and I'm in the backseat [watching her], her breathing has always been normal."
In a new study released Monday in the journal Pediatrics, however, researchers suggested that the car seats could pose a risk to newborn babies -- those younger than 3 months.
But the suggestion elicited strong cautions from medical experts in various fields who pointed out that the risk was largely theoretical and that scaring parents away from using car seats for these children would expose them to real health risks.
Previous studies had brought attention to the risks of car seats in premature babies with very little insight regarding full-term newborns. According to Dr. Bernard Kinane, a pediatrician at Harvard's Mass General Hospital for Children and one of the study's authors, this study is really the first controlled, large-sample examination of variations in blood oxygen levels in newborns kept in different positions, both in and out of the car.
Clinicians have known for some time that changes in posture could affect infants' breathing, especially in regards to the position of their head and neck.
"It's simple; when kids are in a car seat, they tend to have their heads turned down," Kinane said when asked about the study's premise. This sitting position, he said, could very well lead to constriction of a baby's airway.
In the study, 200 2-day-old newborns were placed in three positions -- in a crib, in a car seat and in a car bed. Car beds differ from car seats in that they allow a baby to lay flat while still remaining restrained in a car.
The researches then measured the babies' levels of oxygen saturation, which is the amount of oxygen in the blood compared to the maximum possible amount of oxygen it could carry.
When measuring the oxygen saturation in the different positions in the newborns, the authors found average levels of 97.9 percent for cribs, 96.3 percent for car beds and 95.7 percent for car seats. But the lowest values that the researchers observed in some babies dipped to 83.7 percent for the car bed and 83.6 percent for the car seat. Oxygen saturation levels of less than 90 percent are usually considered low in adults.
However, accepted values for infants cover a wider range, and according to Dr. Elliot Krane, professor of anesthesia and pediatrics at Stanford University, "Being in the 80s [for short time periods] is no big deal."
The authors concluded that parents should limit a newborn's time in a car seat to only the time necessary for travel and no more. They highlighted the fact that some parents keep their newborns in car seats longer, essentially using them like cribs.
But do these changes in lowered oxygen levels matter?
The overwhelming consensus among experts in the fields of pediatrics, neonatology and pediatric anesthesiology was "no."
"The study results are interesting in producing a statistically significant result that does not appear to have any clinically significant implications," said Dr. Steven Donn, a neonatologist and professor of pediatrics at the University of Michigan in Ann Arbor.
Though the authors suggested a link in older children between low oxygen levels with behavioral and intellectual changes and pointed out that the mechanism described in the study could have been partially involved in some rare cases of infant deaths in car seats, none of the experts were able to remember a single case in their clinical experiences in which lowered oxygen levels directly led to injury or death in a newborn.
"I am less concerned than the authors seem to be about long-term consequences of these relatively mild degrees of desaturation," said Dr. Ian Holzman, professor of pediatrics and chief of newborn medicine at Mount Sinai School of Medicine in New York. "To suggest that this may influence future developmental indices seems a bit unlikely and probably does a disservice to an otherwise important safety device."
This sentiment was echoed by Dr. Ira Rubin, a pediatrician in practice in Naperville, Ill. "I don't think that the oxygen saturations mean much since they were not less than 90 percent, and many newborns will be fine if the oxygen saturations are just better than 80 percent," he said.
Pediatricians also noted that in order to realistically scrutinize how a baby's posture in a car seat affects its breathing, one must also look at other postures the baby attains during other activities.
"We also don't know about what [oxygen] saturations are like in any number of other routine circumstances," Krane said, adding that the precise position of the newborns in each of the three devices and the phase of their sleep cycles could also change the measured values.
Dr. F. Sessions Cole, professor and vice chairman of pediatrics and director of newborn medicine at Washington University School of Medicine, pointed out another possible untoward conclusion of the study. "Unfortunately, many parents hold infants in a car seat like position," he said. "I would hesitate to suggest not holding infants based on this study."
Like the experts, first-time mom and anesthesiologist Nair said she understood the theoretical concerns brought to light by the authors. However, despite knowing these risks, she said she feels that in this case, the benefits of her daughter's car seat outweigh the suggestion of risk.
"I'm much more worried about a car accident," she said.