Comparison of neurally adjusted ventilatory assist and synchronized intermittent mandatory ventilation in preterm infants after patent ductus arteriosus ligation: a retrospective study

Patent ductus arteriosus (PDA) is a condition that frequently affects preterm infants, with an incidence of roughly 46% in those less than 32 weeks gestation, and exceeding 70% in infants less than 28 weeks gestation [1, 2]. The condition results from a shunt that directs blood from the aorta to the pulmonary artery, leading to pulmonary congestion and a reduction in systemic blood flow. This in turn results in decreased lung compliance and tissue perfusion [3]. If medical therapy is contraindicated or does not succeed in preterm infants with significant PDA, surgical ligation becomes a necessity. Many premature infants who undergo PDA ligation rely on mechanical ventilation. Consequently, managing their post-surgery respiratory needs is of paramount importance. A key concern is lung immaturity, which can intensify respiratory difficulties in premature infants. Neurally adjusted ventilatory assist (NAVA) is an emerging ventilation mode that could address this issue by detecting diaphragmatic electrical activity to synchronize support with spontaneous breathing [4]. Research indicates that NAVA is both feasible and safe for use in neonates, infants, and children with conditions such as acute respiratory distress syndrome, prematurity, and bronchiolitis [5‐8]. However, there is limited experience in utilizing NAVA in children after congenital heart surgery. This study explores our experiences with NAVA following PDA ligation in preterm infants. We assessed the feasibility of NAVA versus SIMV after PDA ligation in preterm infants using ventilation parameters, oxygenation metrics, and sedation requirements as the basis for comparing the efficacy of the two modes in providing adequate ventilation and oxygenation.

Infants after congenital heart surgery often require mechanical ventilation. However, recently, most infants after cardiac surgery are extubated in the operating room. The exception is patients with complex neonatal congenital heart disease or ligation of the ductus arteriosus in premature infants, which often require prolonged mechanical ventilation. These infants require not only additional respiratory assistance but also comprehensive hemodynamic management, including various inotropes, to sustain sufficient cardiac output and avert cardiopulmonary complications. Additionally, patent ductus arteriosus results in increased pulmonary blood flow and congestion. Coupled with lung immaturity in preterm infants, this congestion leads to a greater need for respiratory support [14]. Therefore, it is very important to optimize the ventilation strategy of the patient’s hemodynamics while avoiding unnecessary increases in medical support. in medical support [15].

At our CICU, it has become standard practice to introduce NAVA to patients following PDA ligation in preterm infants if patient-ventilator asynchrony affects hemodynamics. Because of the immature lung development of premature infants, they are more susceptible to ventilator-associated lung injury (VILI). VILI will aggravate the lung development disorder occurring after birth, causing serious sequelae such as bronchopulmonary dysplasia [16]. The optimal ventilation mode should provide adequate and steady tidal volume and minute ventilation at low airway pressure. It should also be able to rapidly adapt to sudden or unpredictable changes in lung mechanics or patient requirements. NAVA records the EAdi through the esophageal catheter, and the degree of assistance is determined by the patient’s breathing needs, synchronizing the ventilator’s breathing with the patient’s inhalation, thereby reducing the patient’s need for pressure [17]. Crulli et al. conducted a study in 28 children with congenital heart disease after surgery and found that the PIP and MAP were significantly reduced after NAVA respiratory support compared with conventional ventilation [18]. Liet et al. compared hemodynamic parameters in a physiology pilot study of 6 children and found that inspiratory pressure was lower and blood pressure was higher with NAVA compared with conventional ventilation [19]. In our study, a similar situation was observed. That is, the airway PIP and the MAP were significantly reduced compared with SIMV. Furthermore, we found that oxygenation under NAVA was improved over SIMV modes, which was similar to the results of the previous study [17]. Therefore, better oxygenation can be achieved with lower airway pressure under NAVA, which may help minimize ventilator-induced lung injury. This adds to the limited literature in this population.

Our study found that the sedation requirement during NAVA ventilation was significantly lower than that of SIMV ventilation mode. A randomized controlled study of 170 pediatric intensive care patients by Kallio et al. also found less sedation required with NAVA compared to conventional ventilation [20]. Lee et al. retrospectively analyzed NAVA and conventional ventilation in 14 ventilator-dependent preterm infants with bronchopulmonary dysplasia and found that sedation requirements were significantly reduced in the NAVA group [21]. SIMV mostly use pressure-triggered or flow-triggered, both of which have an inherent delay in-breath initiation compared to NAVA. Since the triggering of NAVA is driven by electrical signals from the diaphragm, synchronization of the patient with the ventilator is almost always present. This synchronization between the patient and the ventilator helps minimize patient discomfort and anxiety, with reduced sedation requirements following the administration of NAVA [5, 22].

To the best of our knowledge, this is the first study to document the use of NAVA following ductal ligation in premature babies. However, this study has some limitations. Firstly, since it was a retrospective study, some inherent biases may have arisen. When reviewing the information in the electronic medical record system, we found that the data available did not allow the assessment of patient-ventilator synchronization or work of breathing. Second, this study was performed in preterm infants following ductal ligation surgery, which may hinder the application of the current findings to other infants with congenital heart disease. Moreover, limitations including small sample size, brief observation timeframe, and absence of long-term follow-up could also impact the precision of the findings. Although a small retrospective study, the results suggest the value of NAVA for PDA ligation in preterm infants. Additionally, the results will offer some reference value for further prospective studies moving forward, and encourage the use of NAVA in the perioperative management of congenital heart defects. Other factors like congenital defects, medications, feeds, fluids, ventilator settings, sedation, and anesthesia were uncontrolled. Standardizing these variables in prospective studies is necessary to isolate NAVA’s effects after PDA closure. Moreover, it is important to note that the observed differences in PIP and MAP between the NAVA and SIMV groups may be partially attributed to the use of target tidal volume in the NAVA mode. In NAVA, PIP automatically adjusts according to the patient’s tidal volume, whereas in SIMV, PIP settings require manual adjustment by clinicians. This inherent difference in ventilation strategies could contribute to the observed variations in PIP and MAP between the two groups. However, the early evidence of benefit warrants future rigorous NAVA assessment in this cohort following ductal ligation, while accounting for additional factors, to allow definitive conclusions.

The use of NAVA appears to be feasible in preterm infants after patent ductus arteriosus ligation. Compared to SIMV, early use of NAVA post PDA ligation in preterm infants was associated with decreased PIP and MAP. Early NAVA was also associated with reduced sedation needs and improved oxygenation. Further prospective studies should be conducted to fully evaluate the effects of NAVA in this vulnerable patient population.