Sleeping position, oxygen saturation and lung volume in convalescent, prematurely born infants

Prematurely born infants are often nursed prone in the initial stage of illness, because such positioning is associated with better oxygenation and lung function. However, there has been little research on the effect of sleeping position on convalescent infants. Some studies have suggested that any benefit of the prone position on oxygen saturation at 30-33 weeks' postmenstrual age (PMA) may be small (=2%) and at 36 weeks' PMA may be restricted only to those infants who are oxygen dependent.

Moreover, lung volumes have been shown to be superior in the prone position at 36 weeks' PMA only in infants who are oxygen dependent. Improvement in oxygenation in prone compared with supine position is related to changes in lung volume as well as changes in thoracoabdominal synchrony, ventilation-perfusion heterogenicity and/or intrapulmonary shunting. The latter abnormalities reduce as respiratory distress lessens and PMA increases.

On these basis, a prospective study was conducted in an English tertiary care unit in order to determine whether the effects of sleeping position on lung volume and oxygenation are influenced by PMA and oxygen dependency in convalescent prematurely born infants. In total, 41 Infants born before 32 weeks of gestation, who were at least 32 weeks' PMA and tolerating hourly feeds, without requirement for continuous positive airway pressure or mechanical ventilation, were included into the study.

Infants were studied both supine and prone at two-weekly intervals from 32 weeks' PMA until discharge. Each posture was maintained for 1 h. Pulse oximeter oxygen saturation (SpO2) was monitored continuously, and at the end of each hourly period functional residual capacity (FRC) was measured. Results show that lung volumes were higher in the prone position throughout the study period; there was no significant effect of PMA on lung volumes. Overall, SpO2 was higher in the prone position (p=0.02), and the effect was significant in the oxygen-dependent infants (p=0.03), but not in the non-oxygen-dependent infants. There was no significant influence of PMA on SpO2. In conclusion, this study show that position influenced lung volumes in prematurely born infants from 32 weeks' PMA.

The changes in lung volume, however, were not associated with appreciable changes in oxygenation in infants without respiratory distress. Therefore, it may be possible to suggest that infants who are not dependent on oxygen, from 32 weeks' PMA, should be nursed supine on the neonatal unit. Moreover, it could be recommended to continue oxygen saturation monitoring after 32 weeks' PMA to be certain that longer periods of supine sleeping are not associated with loss of lung volume and hypoxaemia.

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