The effects of sleeping position on ventilatory responses to carbon dioxide in premature infants

Background: The prone sleeping position, particularly in prematurely born infants, is associated with an increased risk of sudden infant death syndrome. A possible mechanism is an impaired ability to respond to respiratory compromise. The hypothesis that the ventilatory response to a carbon dioxide (CO2) challenge in convalescent, prematurely born infants would be lower in the prone compared with the supine position was therefore tested. Methods: In each position, ventilatory responses to increasing levels of inspired CO2 were assessed. The airway pressure change after the first 100 ms of an occluded inspiration (P-0.1) and the maximum inspiratory pressure with an occluded airway during crying (P-imax) were measured; the ratio of the P-0.1 to the P-imax at each inspired CO2 level and the slope of the P-0.1/P-imax response were calculated. Chest and abdominal wall asynchrony was assessed using inductance plethysmography and functional residual capacity (FRC) measured using a helium gas dilution technique. Results: Eighteen infants with a median postmenstrual age of 35 (range 35-37) weeks were studied. In the prone versus the supine position, the mean P-0.1 (p=0.002), the mean P-imax (p=0.006), the increase in P-0.1 with increasing CO2 (p=0.007) and the P-0.1/P-imax response slope (p=0.007) were smaller. Thoracoabdominal asynchrony was not significantly influenced by position or inspired CO2. FRC was higher in the prone position (p=0.019). Conclusions: Convalescent, prematurely born infants have a reduced ventilatory response to CO2 challenge in the prone position, suggesting they may have an impaired ability to respond to respiratory compromise in that position.