Ventilatory response to added dead space and position in preterm infants at high risk age for SIDS

Abstract

International audienceObjective: The vulnerability of prematurely born infants to Sudden Infant Death Syndrome (SIDS) in the prone position might be explained by a reduced ability to respond to a stress, such as hypercarbia, in that position; our objective, therefore, was to further explore the influence of position on the response to a stress. Working hypothesis: The ability of prematurely born infants to respond to added dead space in the prone compared to the supine position would be impaired at the high risk age for SIDS. Patients: Twenty infants, median gestational age of 30 (range 24-32) weeks were studied at a median postmenstrual age (PMA) of 45 weeks. In addition, comparisons were made to the results of 25 infants studied at 36 weeks PMA. Methodology: Infants were studied supine and prone. Breath by breath minute volume was measured at baseline and after a dead space was incorporated into the breathing circuit; the time constant of the response was calculated. The pressure generated in the first 100 msec of an occlusion (P0.1), the maximum inspiratory pressure during an airway occlusion and functional residual capacity (FRC) were also measured in both positions. Results: The median time constant was longer (38 (range 15-85) versus 26 (range 2-40) seconds (p=0.002)). P0.1 lower (p=0.003) and FRC higher (p=0.031) in the prone compared to the supine position. In the prone position, the time constant correlated with PMA (p=0.047), ie. the rate of response to added dead space was significantly damped with increasing postnatal age up to the critical age for SIDS. Conclusions: The dampened rate of response to added dead space in the prone compared to the supine position lends support to the hypothesis that a poorer response to a stress may contribute to prematurely born infants increased risk of SIDS in the prone position

Sleeping position and responses to a carbon dioxide challenge in convalescent prematurely born infants studied post-term

“…In this study, the infants had a significantly lower P 0.1 in the prone compared to the supine position, confirming our earlier findings 6. As above, P 0.1 is influenced by respiratory muscle strength, but we found no significant differences in the Pimax results between positions.…”

“…There was, however, no tendency for differences in the P 0.1 or P 0.1 /Pimax levels between prone and supine to vary by CO 2 level, that is the infants did not have a lower ventilatory response to the CO 2 challenge in the prone compared to the supine position. This does not contradict our previous results6 as we demonstrated a slower ventilatory response to added dead space in the prone compared to the supine position rather than a difference in the size of the response. Indeed, in both positions, the infants were able to fully compensate for the added dead space, but they did it more slowly in the prone position 6.…”

“…This does not contradict our previous results6 as we demonstrated a slower ventilatory response to added dead space in the prone compared to the supine position rather than a difference in the size of the response. Indeed, in both positions, the infants were able to fully compensate for the added dead space, but they did it more slowly in the prone position 6. At 36 weeks PMA, Martin et al 14 reported a reduced response to hypercapnia in the supine position, whereas we found the opposite, that is a reduced ventilatory response to the CO 2 challenge with a smaller P 0.1 /Pimax response slope in the prone position 8.…”

“…We have demonstrated that convalescent prematurely born infants studied post-term had a reduced ability to respond to added dead space (tube breathing) in the prone compared to the supine position 6. The major stimulus during tube breathing is hypercapnia 7.…”

Critical diaphragm failure in sudden infant death syndrome

“…Such increases in EEV can significantly impair diaphragm performance, and, as Rehan and colleagues conclude, ‘in adults, diaphragm strength and endurance as well as the efficiency of breathing are reduced by 40%–50% with this magnitude of increase in lung volume’. Greenough and colleagues have reported similar results in several clinical studies with premature infants and observe that respiratory muscle strength is significantly reduced in the prone compared to the supine position in ( 106–108 ).…”