Respiratory Instability of Term and Near-Term Healthy Newborn Infants in Car Safety Seats

DISCUSSION

Nearly 4 million infants are born each year in the United States, and 4% to 6% are born at 35 to 36 weeks' gestation.⁶Many of these infants are healthy after birth and receive only basic newborn care in the nursery, but our study showed that 12% of these infants experienced apnea and/or bradycardia in their car seats. These findings confirm the recommendation of the AAP that all infants who are born at <37 weeks' gestation receive an individualized car seat evaluation,¹ regardless of whether the infant requires special care after birth. At the initiation of this study, no nurseries in our community were routinely following this recommendation for preterm infants who were hospitalized in the level I newborn nursery. We were concerned that the evaluation may not be warranted in this group of otherwise healthy infants and that the time and expense of doing the evaluation might be burdensome to families and to the nursery staff. However, the results of the study did affirm the need for car seat evaluations in this population, and the process has been accepted as a routine part of care for these patients. Additional difficulties in implementing the policy may apply to nurseries that are not associated with NICUs. For example, hospitals must have expertise with cardiac-apnea monitoring as artifactual tracings are common, and minor events may not be pathologic.

Although only preterm infants experienced apnea and/or bradycardia while in their car seats, the oxygen saturation values of both term and preterm infants declined over the first hour spent in the car seat. As also noted by Willett et al,³ most of the infants maintained oxygen saturation values of >90% throughout the study. However, 7% of infants spent more than 20 minutes in the car seat with oxygen saturation values between 85% and 90%. Steady-state oxygen saturation values below 90% are not normally seen in healthy infants,^{15 ,16} indicating suboptimal oxygenation in the upright position. This degree of hypoxia is not thought to be harmful, but even healthy full-term infants may be vulnerable to more significant hypoxia with prolonged upright positioning, frequent gastroesophageal reflux, or intercurrent respiratory illnesses.

This study was not designed to evaluate the cause of the abnormal events that occurred while infants were seated in their car seats, as this issue has been explored in other studies. Although these events seem to be related to a combination of immature control of breathing and decreased tidal volume in the upright position,⁴ they are not limited to infants with a clinical history of apnea of prematurity.³ All of the infants in our study were admitted to a normal newborn nursery and cared for without apnea monitors. No infant was clinically suspected to have apnea before the study. However, after significant events in their car seats, 1 infant was found to have apnea of prematurity and another was found to have significant gastroesophageal reflux. This circumstantial evidence is consistent with previous findings that infants with apnea of prematurity may experience further problems in their car seats, but infants without clinically detected apnea of prematurity still are at risk.³

The AAP recommends prone or supine positioning in a car bed for an infant with documented oxygen desaturation, apnea, or bradycardia while seated in a car safety seat.¹ Recommendation of a car bed poses problems for families with twins, triplets, or other children, as the Cosco Dream Ride (Cosco, Inc, Columbus, IN) requires >1 space in the car, and the Cherish Car Bed (Graco, Elverson, PA) fits infants who weigh only up to 9 pounds. Families that travel in trucks also may have difficulties using the car bed. When a car bed was not a viable option for families, we retested the infant in a seat of a different design or with the seat at the most reclined angle permitted by the manufacturer, as this was noted to improve oxygen saturation values in a previous study.⁴ Before recommending a car bed, it also is important to consider that the car seat evaluation may unmask an underlying condition that was not suspected previously (eg, apnea of prematurity in a near-term infant, gastroesophageal reflux).⁵ Furthermore, moving the infant to a car bed usually abolishes the events, but this is not always the case.¹⁷ Our current policy is that premature infants from the newborn nursery who fail their car seat evaluations are moved to a car bed and monitoring is continued for an additional hour. Infants who have events either during the baseline supine period or in the car bed typically are admitted to the NICU for additional evaluation.

In addition to the issues of respiratory stability, this study showed that 24% of preterm and 4% of term infants in this study were unable to be positioned securely in modern car seats supplied by their families, despite the use of blanket rolls. This was attributable, in part, to a large variation in the design of many standard infant car seats. Some do not have belt dimensions that currently are recommended for premature infants.² Others have a steep angle of incline that makes it difficult to stabilize the infant's head. In previous studies, the size of the belt dimensions and the use of blanket rolls to stabilize the head and neck of the infant were important in maintaining proper alignment and thus optimizing safety in a crash situation.^{3 ,4 ,8} Proper size of the car seat and positioning of the infant within the car seat also may aid in maintaining a patent upper airway and thus better respiratory stability in these infants.

The AAP recommends that at discharge, every newborn be restrained properly in a car safety seat.¹⁸ Our study results indicate that there are a number of barriers to accomplishing this goal. In our study, 35% of families had no car seat or brought car seats that were unsafe or did not fit despite the use of blanket rolls. Even with modern car seat designs, no newborn infant in our study could be positioned securely without additional padding at the sides, and even full-term infants occasionally required padding at the crotch strap to ensure a secure fit. For preterm infants, parents often are unprepared for the specific car safety seat issues with which they will have to contend, making it difficult to select an appropriate car seat before birth. Most nurseries do not have standard policies to evaluate car seats and to teach parents how to use blanket rolls to position newborn infants properly, but this should be part of the discharge process. Pre- and postnatal education of families, as recommended in the current AAP guidelines,¹⁸ will help families to ensure the safety of their children while traveling in cars. During the course of the study, it became clear that new parents are overwhelmed with information about their newborn and that parents need simple instructions that can be recalled and used easily later. With this in mind, it may be more effective to make car seat manufacturers aware of the issues of positioning and physiologic stability in newborn infants who use their products. Additional studies to define an optimal design for infant car seats would be helpful in ensuring a uniformly secure fit and physiologic stability, thus making it easier for families to use car seats properly without the need for a complicated set of instructions.

Infant car safety seats play an important role in protecting young infants from injury and death in motor vehicle accidents. However, data in this study show that term and preterm infants are equally susceptible to declining baseline oxygen saturation values in car seats. Although car seats often are used as carriers for newborn infants, our data indicate that preterm and term newborns should not remain in car seats for extended periods of time when they are not traveling. The AAP recommends that travel be minimized for premature infants,¹ and our data suggest that full-term newborns also would benefit from this recommendation. In addition, the use of swings and other types of upright seating devices should be uniformly discouraged during the first months of life.