The Effect of Initial Oxygen Exposure on Diaphragm Activity in Preterm Infants at Birth

Background: The initial FiO₂ that should be used for the stabilization of preterm infants in the delivery room (DR) is still a matter of debate as both hypoxia and hyperoxia should be prevented. A recent randomized controlled trial showed that preterm infants [gestational age (GA) < 30 weeks] stabilized with an initial high FiO₂ (1.0) had a significantly higher breathing effort than infants stabilized with a low FiO₂ (0.3). As the diaphragm is the main respiratory muscle in these infants, we aimed to describe the effects of the initial FiO₂ on diaphragm activity. Methods: In a subgroup of infants from the original bi-center randomized controlled trial diaphragm activity was measured with transcutaneous electromyography of the diaphragm (dEMG), using three skin electrodes that were placed directly after birth. Diaphragm activity was compared in the first 5 min after birth. From the dEMG respiratory waveform several outcome measures were determined for comparison of the groups: average peak- and tonic inspiratory activity (dEMG_peak and dEMG_ton, respectively), inspiratory amplitude (dEMG_amp), area under the curve (dEMG_AUC) and the respiratory rate (RR). Results: Thirty-one infants were included in this subgroup, of which 29 could be analyzed [n = 15 (median GA 28.4 weeks) and n = 14 (median GA 27.9 weeks) for the 100 and 30% oxygen group, respectively]. Tonic diaphragm activity was significantly higher in the high FiO₂-group (4.3 ± 2.1 μV vs. 2.9 ± 1.1 μV; p = 0.047). The other dEMG-parameters (dEMG_peak, dEMG_amp, dEMG_AUC) showed consistently higher values in the high FiO₂ group, but did not reach statistical significance. Average RR showed similar values in both groups (34 ± 9 vs. 32 ± 10 breaths/min for the high and low oxygen group, respectively). Conclusion: Preterm infants stabilized with an initial high FiO₂ showed significantly more tonic diaphragm activity and an overall trend toward a higher level of diaphragm activity than those stabilized with an initial low FiO₂. These results confirm that a high initial FiO₂ after birth stimulates breathing effort, which can be objectified with dEMG.