Vulnerability of respiratory control in healthy preterm infants placed supine☆,☆☆,★

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Abstract

Objective: We tested the hypothesis that healthy preterm infants have attenuated ventilatory responses to hypercapnia, associated with a decreased rib cage contribution to ventilation, in the supine versus prone position. Study design: We elicited hypercapnic ventilatory responses from 19 healthy preterm infants (postconceptional age 35 ± 1 weeks) who were being prepared for hospital discharge. The O2 saturation was continuously monitored. Before and during CO2 rebreathing, ventilation was measured with a nasal mask pneumo-tachygraph and was derived from chest wall motion as determined by respiratory inductance plethysmograph. This measuring method allowed us to compare both ventilation and the percentage rib cage contribution to ventilation between supine and prone positions. Statistical analysis employed analysis of variance with repeated measures. Results: The supine position was associated with a higher respiratory rate (p<0.02) and lower O2 saturation (p <0.007) than the prone position. The increase in ventilation in response to hypercapnia was lower in the supine than in the prone position. This was statistically significant for the respiratory inductance plethysmograph (p <0.008) but not the pneumotachygraph (p =0.077), and was associated with a smaller rib cage contribution to ventilation in the supine than in the prone position (p <0.0001). Conclusion: Respiratory control may be vulnerable when healthy preterm infants are placed supine. Widespread avoidance of the prone position may not be appropriate for such patients. (J PEDIATR 1995; 127:609-14)

Section snippets

METHODS

The study population consisted of 19 healthy premature infants (14 girls), with a gestational age of 29.8 ± 2.6 weeks, birth weight 1376 ± 425 gm, postnatal age at study 5.3 ± 3.1 weeks, postconceptional age at study 35.2 ± 1.4 weeks, and weight at time of study 1876 ± 135 gm (all expressed as mean ± SD). The infants were clinically stable and receiving all nutrients enterally. No infant was receiving supplemental O2 at the time of study, and theophylline therapy had been discontinued in all of

RESULTS

Ventilatory measurements derived from the pneumotachygraph, end-tidal PCO2, and O2 saturation are summarized in the Table during normocapnia and hypercapnia in each sleep state and position. The supine position was associated with a higher respiratory rate (p <0.02) and lower O2 saturation (p <0.007) than the prone position across sleep states and levels of CO2. Tidal volume and minute ventilation did not differ significantly between positions.

As anticipated, inhalation of CO2 increased

DISCUSSION

These results indicate that stable preterm infants have attenuated ventilatory responses to hypercapnia when placed in the supine versus the prone position. This was documented by the respiratory inductance plethysmograph and further supported by the nasal mask pneumotachygraph measurements. We propose that a diminished hypercapnic ventilatory response in supine preterm infants before their hospital discharge may have implications for their respiratory stability.

Previous studies have

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    ☆

    From the Divisions of Neonatology and Pediatric Pulmonology, Department of Pediatrics, Case Western Reserve University School of Medicine and Rainbow Babies and Childrens Hospital, Cleveland, Ohio

    ☆☆

    Reprint requests: Richard J. Martin, MD, Rainbow Babies and Childrens Hospital, Department of Pediatrics, 11100 Euclid Ave., Cleveland, OH 44106.

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    0022-3476/95/$5.00 + 0 9/23/67089

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