Introduction

Over the past few decades, avoidance of invasive mechanical ventilation (IMV) and promoting of the use of non-invasive ventilation (NIV) in infants born prematurely has been accepted as a standard of care to reduce lung injury and subsequent development of bronchopulmonary dysplasia (BPD) [1]. Although nasal continuous positive airway pressure (nCPAP) is the most frequently used NIV mode for infants born before 32 weeks gestation, NIPPV was found to decrease the incidence of reintubation within 2–7 days of life compared to nCPAP [2]. Furthermore, synchronized NIPPV is considered the most effective NIV in preventing extubation failure in preterm neonates with respiratory distress syndrome [3]. The advantages of NIPPV over nCPAP include the ability to deliver higher mean airway pressure (MAP) and carbon dioxide (CO2) clearance [4, 5].

Recently, neurally adjusted ventilatory assist (NAVA) for invasive and non-invasive ventilation (NIV-NAVA) has emerged as a new respiratory support mode for preterm infants with respiratory insufficiency. Typically, NAVA mode (invasive and non-invasive) uses the electrical activity (Edi) of the diaphragm to trigger, set the amount of pressure, and cycle off the ventilator which in turn reduces asynchrony during NIV [6, 7]. In comparison to NIPPV, several studies have reported that NIV-NAVA is associated with a higher success rate of preventing reintubation [8,9,10], alongside fewer episodes of bradycardia and apnea of prematurity per day [11]. However, data regarding the effect of NIV-NAVA compared to NIPPV on diaphragmatic function and dimensions in preterm infants remains unknown.

Lung ultrasound (LU) has been increasingly used in neonates as a non-invasive and radiation-free imaging modality to assess lung aeration and diaphragm function. Moreover, there is a growing interest among researchers in using ultrasound to monitor the evolution of diaphragmatic contractility and dimensions during IMV, for clinical and research purposes [41].

We acknowledge our study limitations. First, we had a small sample size that could be attributed to interrupted/low recruitment rate due to the COVID-19 pandemic. Second, the study design was based on consecutive recruitment of all eligible patients but lacked randomization. Thirdly, we did not do a serial ultrasonographic assessment to evaluate the changes of diaphragmatic dimensions and functions over time while infants were supported by these two types of NIV. Another limitation is that infants in the NIV-NAVA group were scanned after short duration post transitioning from NIPPV and the risk of “carryover effect” cannot be ruled out completely. Finally, diaphragm ultrasound is operator dependent; therefore, some variations in the measurements are not uncommon. However, our study results have shown high interobserver reliability which validate, to some degree, the study findings.

Conclusion

In infants born at < 30 weeks’ gestation, NIV-NAVA was associated with significantly higher DE compared to NIPPV reflecting improvement in the diaphragmatic functions. There were no significant differences regarding other measurement such as DTexp, DTins, DTF, and LUS. Further studies, with a larger sample size and serial assessment of the diaphragm are needed to draw a firm conclusion.