What is already known on this topic
- Both preterm and term infants can show respiratory compromise when placed to sleep in a car seat.
- Car seat trials have been recommended for preterm infants to assess individual risk of respiratory compromise in a car seat before discharge from the neonatal unit without good evidence of their efficacy or accuracy.
Our study shows that a clinical car seat test by a nurse can detect infants with increased obstruction in a car seat but will not detect all infants at risk. In addition, it may assess infants as being at risk when they are no less stable in a car seat than in a cot. This can cause anxiety to parents and result in delay of discharge with no evidence of benefit to the infant. Preterm infants ready for discharge from the neonatal unit in this study had variable and individual cardiorespiratory responses, as measured by PSG, to being placed in a car seat during sleep. Although there were no group differences in the amount of obstruction apnoea experienced by infants after transfer to the car seat some infants did seem to have increases in obstructive apnoea in the car seat at a level that may be clinically important. Immaturity was the most consistent risk factor for cardiorespiratory instability, which occurred in both the cot and car seat. Infants at 35 weeks' PMA are now often being discharged and these infants continue to have respiratory events not recognised by event monitors or staff.22
The strength of our study is that both obstructive and central apnoea were considered as well as the effect of respiratory events on oxygenation. Apnoeas
5 s in length or shorter if associated with a greater than 2% desaturation were included for analysis although it is not clear if all these apnoeas are clinically notable. For this group of infants the range of values for the lowest saturation after apnoea recorded in active sleep was 71–93% for the time in the cot and 76–94% for the period in the car seat. Despite this, prolonged (
1 min) desaturation to <85% was seen in only three infants, two while in the cot and one while in the car seat.
Preterm infants are prone to obstruction particularly with neck flexion.24
Four of the five infants with an increase in obstruction were not yet term corrected age. Vulnerability to obstruction has been postulated as a reason for respiratory compromise in preterm infants in car seats but despite this few studies have measured obstructive apnoea. Willett et al
studying preterm infants ready for discharge found obstructive apnoea was uncommon and not apparently exacerbated by the car seat.3
However many events were associated with what were described as short (5–20 s) mixed apnoeas. Others have shown that keeping the head in the neutral position while the infant is in the car seat can improve the size of the airway.25
In this study the nurse‐observed predischarge test did not detect apnoea in any infant by apnoea monitor. Apnoea monitors that depend on abdominal movement will not pick up obstructive apnoea and impedance monitoring can also miss apnoea in preterm infants.26
We used PSG as the gold standard for detection of apnoeic episodes, allowing us to differentiate obstructive from non‐obstructive events. Most infants with obstruction in the car seat were observed to be in respiratory distress. This assessment can be taught to parents without the need for a car seat test.
What this study adds
- Preterm infants can show as much or even more compromise in a cot after a feed than is seen when they are sleeping in a car seat.
- Some, but not all, preterm infants have an increase in obstructive apnoea after being moved from a cot to a car seat to sleep.
- An observed car seat trial does not reliably pick up all adverse respiratory events experienced by preterm infants while sleeping in a car seat and may produce false positive results, which could potentially delay infant discharge.
Gastro‐oesophageal reflux seemed to be uncommon and more likely during the period in the cot after a feed. This suggests that gastro‐oesophageal reflux is not a major reason for the obstruction experienced by preterm infants in car seats although we may have missed some non‐acid reflux. Not studying the infants in the car seat after a feed may have affected the results by increasing the level of obstruction seen in the car seat, but local clinical practice guidelines recommend that infants should not be placed in a car seat immediately after a feed.
We used the car seat provided by parents even though this meant a variety of car seats were studied. As none of these seats are specifically designed for such small infants it seemed reasonable to use whichever car seat the parents provided as this reflected the current clinical approach in the unit. This meant that for four infants the car seat design was such that the back of the seat was originally set at a 60° angle rather than at 45° as most car seats were. Car seats angled at 60° seemed to be not as well tolerated as those angled at 45° although our numbers were too small to confirm that the angulation of the car seat was a risk factor for obstruction.
A small decrease in central apnoea was seen after transfer to the car seat. This was only just significant and may not be clinically important. All central apnoeas
5 s in length were scored whether or not they were associated with oxygen desaturation or arousal. Periodic breathing was not scored separately. Central apnoea is common in preterm infants of this corrected gestation, and currently there are no clear guidelines about which patterns of central apnoea should be considered clinically noteworthy.
This study deemed a nurse‐led car seat trial not to be accurate enough to warrant use in our neonatal unit. We are still concerned about the vulnerability of infants in car seats and have chosen to use the equivalent amount of nursing time to educate caregivers more specifically about use of the car seat and how to recognise signs of respiratory distress. We advise parents to use car seats that do not have a steeply angled back. Caregivers are also instructed that immature infants being discharged from the neonatal nursery should be watched carefully while in the car seat and transferred back to their cot as soon as possible after the car journey ends.