• sids
• epidemiology
• general paediatrics

For more than 25 years we have known that infants placed prone for sleep are at increased risk of dying unexpectedly, and avoiding the prone sleep position for infants leads to a much lower incidence of such deaths.1 2 What is less clear, despite many published investigations into the physiology and possible pathophysiology of sleep position in infants, is why this is the case.

Multiple hypotheses of varying credibility have been proposed to account for the association between infants sleeping prone and increased risk of unexpected deaths,3 4 but no single clear pathophysiological mechanism has yet been identified to fully explain the link between observed physiology and the pathway leading to death. Physiological studies to date suggest the possibility of multiple, probably interacting mechanisms making infants more vulnerable in the prone sleep position.

Several physiological features of the prone sleeping position in infants have been identified:

• The arousal threshold is higher and the ratio of subcortical to cortical arousals is lower when prone than when supine.5

• Heat loss is reduced when prone compared with when supine.6

• In growing preterm infants, the ventilatory response to inhaled carbon dioxide is lower when prone than when supine.7

• Baroreflex sensitivity as assessed by the response …