Weight and Age as Predictors for Passing the Infant Car Seat Challenge

DISCUSSION

Car seats are essential for preventing death or injury to newborns and infants during motor vehicle travel¹⁴; however, most car safety seats are designed for the “average” term newborn infant, so many preterm infants who are discharged from the hospital may face specific issues when using standard infant car safety seats. Specifically, they may be prone to respiratory compromise. Early studies noted that preterm infants who were otherwise ready for hospital discharge had frequent episodes of hypoxia during a 90-minute observation period, and the incidence of hypoxia was inversely related to birth weight and GA at birth.^10,15,16 Since then, other at-risk populations of infants have been identified.^17,18 Furthermore, we have found from our experience in the CHILD Clinic and from previous investigation that many infants who fail the ICSC are late preterm infants who were born between 35 and 37 weeks' GA.⁸ Although no long-term studies have determined the prognostic implications of the intermittent oxygen desaturation described in infants who fail the ICSC, the adverse effects of intermittent hypoxia from other disease processes have been well-described¹⁹; therefore, the observation that some preterm infants and infants who are at risk develop breathing problems in standard car safety seats has resulted in the need for informed recommendations regarding the proper screening procedures and equipment that is needed for transporting these infants.

The preterm birth rate has remained constant at nearly 13% for the past several years in the United States, translating to an estimated 500 000 preterm infants who are eligible for ICSCs.⁶ The exact number of infants who fail their ICSC is not known, although 1 single distributor of infant car beds in the United States reported to have sold >4000 car beds in 2009 (private communication). On the basis of estimates of prevalence of ICSC testing and published reports of ICSC failure rates,^4,10 it is likely that >20 000 infants in the United States fail their ICSC each year.

Many neonatal units and special care nurseries that discharge preterm infants in the United States have incorporated ICSCs into their routine discharge assessment for preterm infants; however, some late preterm infants may not require special care or intensive care after birth. This is concerning because only 22% of well-infant nurseries (level I) performed ICSCs according to 1 published report, whereas frequencies reported for specialized newborn care nurseries was much higher (81% for level III and 91% for level II).⁷

The AAP's recommendation to perform some form of ICSC does not include specific guidelines for screening infants; therefore, as may be expected, there is wide variation between units in the duration of observation and monitoring and the criteria for passing the test. Consistent with the recently published AAP guidelines,³ our CHILD Clinic studies children for 90 minutes and records all oximetry data continuously to eliminate artifact and to obtain a minimum of 60 minutes of interpretable data.

In addition to the variability in the testing procedures, there is considerable variation in the recommendations given to parents of infants who fail the ICSC. Some advocate for the use of inserts to provide additional postural support, although the use of these supports does not eliminate oxygen desaturation events.^20,21 Others delay hospital discharge until the infant passes the test, but prolonging hospitalization can add to the financial and emotional costs for the family. The 2009 AAP guidelines recommend use of a car bed that meets Federal Motor Vehicle Safety Standards 213 and that allows an infant to travel supine rather than upright, eliminating slouching that has been hypothesized to cause the observed compromise in respiratory function. In our center, we repeat the ICSC in the car bed to document resolution of respiratory compromise, because rarely a nonpostural cause of respiratory compromise may be determined. We have received anecdotal reports of infants who received a diagnosis of congenital heart disease after a failed ICSC; in addition, we have detected a pneumothorax in an otherwise healthy infant who was brought to the NICU for an ICSC.

Car beds occupy more space than a traditional car seat, and the use of a car bed may create anxiety in families who perceive the assignment of their child to a different mode of transportation as a form of stigmatization. Most parents in our clinic have expressed intense desire to transition from the car bed to the car seat, but guidelines to do so safely are not available. Regardless, infant car seat safety experts and the AAP agree that before discontinuing the use of a car bed, a follow-up study should be arranged to determine whether the infant can travel safely in a semireclined position without apnea, bradycardia, or oxygen desaturation.³

To our knowledge, this is the first study to describe the follow-up evaluation of infants who failed their initial ICSC. In a previous survey study of primary care pediatricians in Massachusetts, we noted that a majority of providers used some form of weight or age to guide their decision about when to transition from car bed to car seat. We hoped that the analysis of these infants would provide a minimum age or weight that predicted successful passage of the ICSC, eliminating the need for repeat testing. This study demonstrates that a majority (88%) of infants do pass the ICSC when performed within 5 to 8 weeks of the initial test. We noted that neither weight nor age seemed to be predictive factors for passing the ICSC. Unfortunately, our analysis suggests that repeat testing is the only way to determine definitively whether an individual infant passes or fails and therefore is ready to transition to the car seat.

Our study has several important limitations. First, this study was retrospective and potential predictors were assessed by medical chart review. Second, our testing method included recorded oximetries and heart rates but did not include impedance apnea monitoring; however, our review of all of the records of infants who failed initial ICSCs with impedance monitoring in place demonstrated that no child failed from isolated apnea without associated desaturation or bradycardia. Consistent with this finding, the literature describes that documented ICSC failures are primarily attributable to desaturations and rarely, if ever, to apnea. Third, 1 of our criteria for failure was an oxygen saturation of <90% for >20 seconds. It has been suggested that an oxygen saturation of <93% may be more appropriate.^19,22 We chose to use an oxygen saturation of <90% as our criterion for several reasons:

1. In a previous study, we found that it is rare for an infant to fail an ICSC when the oxygen saturation range is 90 to 92 and that most infants failed their ICSC with profoundly low oxygen levels.⁸

2. Our inpatient unit and many of the surrounding health care facilities use <90% as criterion for failure; we wanted to use a consistent criterion so as not to confuse parents.

3. Our criterion includes a provision that permits the clinician to assign a failed status if the infant demonstrates increased work of breathing or exhibits frequent brief oxygen desaturation events even when they do not meet the explicit criteria for failure. We believe that this provision adds a level of protection for the infant by enabling the clinician to use observation skills to help detect infants who are having trouble in their car seat even when they meet the explicit criteria for a pass.

4. The minimal levels for target mean baseline saturation at all times and the minimal level to use for a single desaturation episode during a 90-minute screening test may not need to be identical. Additional study into the significance of intermittent brief episodes of desaturation versus longer or more frequent episodes of desaturation is certainly warranted.

Fourth, another possible predictor of ICSC failure, head control, was not assessed in this study. In our survey of pediatricians in Massachusetts that we used to guide this study, head control was not frequently used to transition infants from a car bed to a car seat; however, we believe that there are a number of potential risk factors for car seat–related oxygen desaturation that warrant additional study, such as head control and sleep state.^23,24 Investigation of head control and sleep state requires sensitive and highly accurate measurement techniques; previous studies lacked these sensitive measures, and therefore associations between sleep, head control, and car seat–related oxygen desaturation have not been confirmed.^23,24

Fifth, this study used a convenience sample of children who failed an initial ICSC and were referred to the clinic; however, review of the infants who failed initial testing but were not referred to our clinic had similar clinical characteristics to those who were referred. Finally, although this is the largest description of infants who have failed the ICSC, the sample size may be too small to detect predictors successfully. Standardization of the ICSC would enable tracking of characteristics of infants who pass and fail the ICSC on a larger scale and would potentially assist in identifying risk factors for ICSC failure.