Lung volume changes during apnoeas in preterm infants.

OBJECTIVE

Mechanisms of non-invasive high-frequency oscillatory ventilation (nHFOV) in preterm infants are unclear. We aimed to compare lung volume changes during apnoeas in preterm infants on nHFOV and nasal continuous positive airway pressure (nCPAP).

METHODS

Analysis of electrical impedance tomography (EIT) data from a randomised crossover trial comparing nHFOV with nCPAP in preterm infants at 26-34 weeks postmenstrual age. EIT data were screened by two reviewers to identify apnoeas ≥10 s. End-expiratory lung impedance (EELI) and tidal volumes (VT) were calculated before and after apnoeas. Oxygen saturation (SpO2) and heart rate (HR) were extracted for 60 s after apnoeas.

RESULTS

In 30 preterm infants, 213 apnoeas were identified. During apnoeas, oscillatory volumes were detectable during nHFOV. EELI decreased significantly during apnoeas (∆EELI nCPAP: -8.0 (-11.9 to -4.1) AU/kg, p<0.001; ∆EELI nHFOV: -3.4 (-6.5 to -0.3), p=0.03) but recovered over the first five breaths after apnoeas. Compared with before apnoeas, VT was increased for the first breath after apnoeas during nCPAP (∆VT: 7.5 (3.1 to 11.2) AU/kg, p=0.001). Falls in SpO2 and HR after apnoeas were greater during nCPAP than nHFOV (mean difference (95% CI): SpO2: 3.6% (2.7 to 4.6), p<0.001; HR: 15.9 bpm (13.4 to 18.5), p<0.001).

CONCLUSION

Apnoeas were characterised by a significant decrease in EELI which was regained over the first breaths after apnoeas, partly mediated by a larger VT. Apnoeas were followed by a considerable drop in SpO2 and HR, particularly during nCPAP, leading to longer episodes of hypoxemia during nCPAP. Transmitted oscillations during nHFOV may explain these benefits.

TRIAL REGISTRATION NUMBER: ACTRN12616001516471.