Rebreathing is a model for the relationship between a prone sleeping position and sudden infant death syndrome. This study used a mechanical simulation model to establish the relationship between types of bedding and rebreathing potential for an infant placed prone (face down) at different postnatal ages. The infant mannequin was connected to a respirator set to deliver physiologically appropriate combinations of tidal volume (VT) and respiratory rates (RR) across a range of postnatal ages (0-18 months). Before measurements were made, CO2 flow was regulated to 5 ± 0.1% of end-tidal PCO2 (EtCO2). After the model was placed in a prone position, any increase in the fractional concentration of inspired CO2 (FiCO2) was measured. FiCO2 increased immediately and rapidly, and reached a maximum value within a few minutes. The maximum FiCO2 ranged from under 2% to over 10%, depending on the bedding. FiCO2 was also affected by VT and RR. This model is not applicable to actual infants because of the large tissue stores of CO2 in infants; however, it is useful for evaluation of gas diffusibility of bedding and will simplify the investigation of sleeping environments when a baby is found dead with its face covered by soft bedding. In general, the higher the FiCO2, the greater the rebreathing potential. Theoretically, considering the paucity of body stores of O2, changes in FiO2 would be affected not by changes in FiCO2, but by CO2 production and gas movement around the infant's face. The rapid decrease of FiO2 is approximated at the inverse of the FiCO2 timecourse, suggesting the significance of not only CO2 accumulation but also O2 deprivation in the potential space around the baby's face.
- Mathematical evaluation
- Respiratory simulation
- Sudden infant death
ASJC Scopus subject areas
- Pathology and Forensic Medicine