Diminished Response to Carbon Dioxide in Premature Infants

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Abstract
Reduced ventilatory response to CO2 (less than 50 cm3/min/mm Hg increase in minute ventilation) has been demonstrated in premature infants of 28–32 weeks postconceptional age. Diminished ventilatory response to CO2 may be due either to mechanical limitations on respiratory work or true loss of chemosensitivity. Although premature infants are neurologically immature they have been shown to have chemoreceptor activity for oxygen. They are also known to have stiff lungs and high total pulmonary resistance. The present study was undertaken to determine if mechanical or neurological factors limited CO2 response of premature infants. Adult patients have been shown to increase work during CO2 stimulation even though they do not increase minute ventilation as much as healthy subjects. Pulmonary work was therefore calculated from tracings of tidal volume and intraesophageal pressure during rebreathing of 5%CO2 – 40% O2 on 13 occasions in 12 infants. Evidence of CO2 sensitivity, demonstrated by increased respiratory work, was found in 5 of 7 infants who failed to increase minute volume in response to CO2. Two infants increased neither minute volume nor respiratory work, suggesting true absence of chemoreceptor activity. Both mechanical and neurological factors may limit the response to CO2 in premature infants.

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