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

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 (CO(2)) challenge in convalescent, prematurely born infants would be lower in the prone compared with the supine position was therefore tested.

In each position, ventilatory responses to increasing levels of inspired CO(2) 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 CO(2) 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.

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 CO(2) (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 CO(2). FRC was higher in the prone position (p=0.019).

Convalescent, prematurely born infants have a reduced ventilatory response to CO(2) challenge in the prone position, suggesting they may have an impaired ability to respond to respiratory compromise in that position.