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Case–control study
Sleep position does not appear to influence the risk of extreme cardiorespiratory events in vulnerable infants
  1. Dawn E Elder
  1. Department of Paediatrics and Child Health, University of Otago Wellington, Wellington, New Zealand
  1. Correspondence to : Dawn Elder
    Department of Paediatrics and Child Health, University of Otago, Wellington, PO Box 7343, Wellington 6242, New Zealand; dawn.elder{at}

Statistics from

Commentary on: Lister G, Rybin DV, Colton T, et al. Collaborative Home Infant Monitoring Evaluation (CHIME) Study Group. Relationship between sleep position and risk of extreme cardiorespiratory events. J Pediatr 2012;161:22–5.

Implications for practice and research

  • Extreme cardiorespiratory events can be documented during sleep and are more common in immature preterm infants.

  • The supine sleep position does not appear to decrease the risk of Sudden Infant Death Syndrome (SIDS) by decreasing the risk of extreme cardiorespiratory events in vulnerable infants.

  • Reasons for the physiological advantage of the supine sleep position remain speculative and require ongoing study despite decreases in SIDS death rates in recent years.


Despite the successful worldwide introduction of preventative measures to decrease the risk of infants dying of SIDS the final mechanism of death in these infants has not been fully elucidated. While it has been established that placing infants supine for sleep significantly decreases the risk of sudden infant death, theories put forward to explain the physiological advantage of the supine sleep position and disadvantages of the prone sleep position remain speculative.1 Lister et al report further data from the Collaborative Home Infant Monitoring Evaluation (CHIME) research group that help to complete another piece of this puzzle. The group have previously reported that ‘extreme events’ (defined as an apnoea ≥30 s in length or significant bradycardia) are more common in preterm infants and more frequently seen in the first 3 weeks post-term corrected age.2


The CHIME study is a multicentre study initiated in the 1990s to determine whether home cardiorespiratory monitors are effective in monitoring infants at risk of SIDS. The study includes healthy term infants, preterm infants, siblings of infants who died of SIDS and infants who had experienced an apparent life-threatening event. The CHIME study monitor used for data collection records respiratory movement, ECG, pulse oximetry and position. In the current study, infants (n=116) from a cohort of just over 1000, documented as having at least one extreme event (EE) were matched with two control infants without any EE to determine the relationship between sleep position and risk of an extreme cardiorespiratory event. Control data were matched to the first EE recorded for each case infant


The cases and controls (n=231) were well matched with regard to demographic and clinical data. At the point of analysis 36% of cases and 42% of controls were supine, 16% and 18%, respectively, were prone and 47% and 40% in a side/indeterminate position. Neither the prone nor side/indeterminate position was associated with an increased risk of having an EE even after adjusting for potential confounders.


As the authors discuss, these data suggest that the mechanism by which the supine position decreases the risk of SIDS is independent of an effect on prevalence of extreme cardiorespiratory events. The authors also point out that the data presented cannot disprove the possibility the EEs are markers of an infant at risk of SIDS. It is of interest that the proportion of infants sleeping supine was relatively low. As these were mostly preterm infants studied between 1994 and 1998, parents may have been influenced by how their baby was positioned in the neonatal unit.3 The mean postmenstrual age at the time of event analysis was 40 weeks for both groups so infants are not likely to have changed position significantly without assistance. The first EE recorded was used for comparison to specifically rule out the potential bias of a parental change in sleep position in response to experience of an initial extreme event.

These data suggest that the supine sleep position does not decrease the risk of EEs but it remains possible that it provides some protection from the adverse physiological effects that might be associated with an EE. For example, extreme bradycardia is likely to result in a decrease in cerebral perfusion and cerebral oxygenation is already compromised in the prone position.4 No information is provided about whether any changes in oxygenation associated with EEs varied quantitatively with sleep position. Like most research endeavouring to find explanations for sudden infant death, this latest report from the CHIME study group answers one question while highlighting some of the unanswered questions in this area of research and stimulating us to ask many more.

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  • Competing interests None.

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