PEDIATRICS Vol. 104 No. 2 August 1999, pp. 263-269
Why the Prone Position Is a Risk Factor for Sudden Infant Death Syndrome
Received Oct 28, 1998; accepted Mar 15, 1999.
,
; and Megan Page*,
From the * Department of Neonatal Medicine, Royal Prince Alfred
Hospital, Camperdown, Australia; and the Department of Obstetrics
and Gynecology, University of Sydney, Sydney, Australia.
Introduction. The laryngeal chemoreflex may explain why prone sleeping increases the risk of sudden infant death syndrome (SIDS). Swallowing and arousal are crucial to prevent laryngeal chemoreflex stimulation. Our aim was to examine these reflexes and breathing responses in healthy neonates after pharyngeal infusion of water in the supine versus the prone position, controlling for sleep state.
Methods. A total of 10 term infants were recruited after
parental consent and ethics approval. Polygraphic recordings included
sleep state (active and quiet sleep by electroencephalogram, eye
movements, breathing, and behavior), cardiorespiratory measurements
(nasal airflow, chest wall movements, heart rate, and oxygen
saturation), swallowing, and esophageal activity (solid state pressure
catheter). Initial sleeping position was assigned randomly.
Measurements were made for 1 minute before and after 0.4 mL of water
was instilled into the oropharynx. To detect a 30% decrease in
swallowing, power analysis indicated that 
10 babies were required.
Analysis, blinded to position, was made using nonparametric
statistics.
Results. Of the 164 infusions, the most commonly evoked
airway protective responses to pharyngeal infusion were swallowing
(95%) and arousal (54%). After infusion in active sleep, there was a
significant reduction in swallowing and breathing when the prone
position was compared with the supine position (prone: 21.3 [1.0] swallows/min and 
9.6 [2.1] breaths/min; and supine: 32 (2.2) and 2.9 (1.5), respectively). However, there was no difference
in the occurrence of arousal after water infusion.
Conclusion. These data suggest that airway protection is compromised in the prone sleeping position during active sleep, even in healthy infants exposed to minute pharyngeal fluid volumes of 0.4 mL. This is because swallowing rate is reduced significantly, and there is no compensatory increase in arousal. The reduction in airway protective reflexes when in the prone position and in active sleep may be the mechanism for the increased risk of SIDS in the prone position. Key words: SIDS, prone sleeping, apnea, laryngeal chemoreflex, swallow.
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