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The report by Richardson et al in this issue of The Journal, adds to their extensive past studies on arousal from sleep in infants 1. The present work on arousals in swaddled infants is an important addition to the literature. As the author’s indicate, swaddling has become a much more common practice in the U.S. than it was in the recent past. Historically, swaddling was, for the most part, a universal practice prior to the eighteenth century. The present work by Richardson et al is unique in that arousal to a tactile stimulus is reported as opposed to spontaneous arousals.
Richardson et al address several important issues. First, is a low threshold for arousal necessarily a good thing? This may not be the case because cortical arousals may be disadvantageous in certain situations 2. Cortical arousal in infants is often accompanied by hypoventilation especially with crying, which can precipitate sudden severe desaturations in an infant in an asphyxial rebreathing environment. In certain cases this may precipitate sudden unexpected death 3. Moreover, frequent arousals, caused by a low arousal threshold may result in habituation and thereby increase the theshold for arousal, which would be disadvantageous in asphyxia-induced arousals. Fortunately in the present study, as noted previously, swaddling does not appear to impair sub-cortical arousals that are essential for adequate pulmonary function and appear to be the primary mechanism in terminating obstructive apneas in infants 2, 4.
Does the tactile stimulus employed by Richardson et al adequately reflect arousal caused by asphyxia? This is highly relevant because asphyxial and/or hypoxia is widely believed to be major preceding event leading to SIDS deaths. How accurately arousal to a tactile stimulus correlates with that caused by asphyxial stimuli remains unclear. Certainly cortical arousal is needed to escape from life threatening asphyxiating environments either by change in head position or when crying alerts caretakers to a dangerous situation. Equally relevant is that cortical arousal does not appear to be necessary for terminating central or mixed apnea in infants 5,6,7, hence, impairment of cortical arousal associated with swaddling might not be a disadvantage in terminating these types of apnea.
Can swaddling actually increase the risk for SIDS as suggested by the Author’s? This is certainly true for prone sleeping infants 8. In this case, head lifting and turning to avoid an asphyxial environment are impeded when the arms are restrained at the baby’s side rather than positioned beside the infant’s head. In contrast the mechanisms of swaddlings effect on decreasing SIDS risk in supine infants seem clear. An immobilized infant can’t crawl into dangerous asphyxiating environments. Also, swaddling prevents infants from pulling bedding over their heads. Both are risk factors for accidental suffocation and/or SIDS. The only evidence for an increased SIDS risk in swaddled infants comes from a non-peer reviewed abstract 9. Significantly, this study did not distinguish between infants swaddled when prone vs. infant’s swaddled supine. As indicated above, prone swaddled infants are at greatly increased risk for SIDS 8. Particularly relevant here, is that two published studies found that swaddling actually reduces SIDS risk when infants sleep in the supine position 8, 10.
However, the potential dangers of swaddling infants should not be entirely dismissed. The authors have confirmed prior studies indicating that swaddling is associated with increased respiratory rate 11,12. As the author’s surmise, this is likely due to decreased functional residual capacity resulting from increased extra thoracic pressure. In theory decreased functional residual capacity might be deleterious in certain situations where pulmonary function is compromised as in the case of viral pneumonia. Also one might expect that cough might be compromised because forceful coughing must be preceded by inhalation that increases lung volume. Notably a popular publication giving advice to parents recommends that the tighter the swaddle the better the calming effects on infants 13. Taking all this into account, caretakers need some simple method for determining thoracic pressure in swaddled infants to insure that the thoracic pressure imposed that does not compromise lung function and still preserves its calming effects.
In summary, the present article adds significant new information on arousal thresholds to tactile stimuli in swaddled infants. However, it should be noted that currently there is insufficient evidence that infants swaddled while supine are at any increased risk for SIDS. All in all it would appear that the advantages of swaddling supine sleeping infants outweigh the risks, if any.
This research was funded by National Institute of Child Health and Human Development Grant HD-10993.
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