LAUSR

We appreciate Dr. Mandal’s et al. [1] thoughtful letter in response to our article “Dynamic PEEP Study: A Noninvasive Diagnostic Exam to Assess for Effective PEEP in Children with Severe BPD” [2]. Regarding the comment about PEEP levels and patient position, we agree that PEEP can influence lung volumes and pulmonary compliance. In contrast, overt use of PEEP can lead to dynamic hyperinflation and air trapping. Thus finding the adequate PEEP level for each patient is particularly important for clinical management, which was the primary goal of our study. The authors inquire about the role of prone positioning and PEEP levels. We agree that prone positioning influences functional residual capacity and oxygenation in ARDS, which can be seen early in life in severely premature infants [3]. The manuscript by Aguirre-Bermeo et al. [4] cited by the authors involves an adult population with ARDS where indeed changes in positioning improved oxygenation (Pa/FIO2) and decreased lung strain. However, infants with established severe BPD have different respiratory mechanics with very heterogeneous lungs characterized by regions with varying airway resistance, compliance, and time constants [5, 6]. In this setting, prone positioning does not provide the same impact that in ARDS. In addition, prone positioning for daily care, including physical and occupational therapy, is not ideal in chronic patients, such as patients with severe BPD. In terms of ventilator parameters, we used a strategy based on this particular population's respiratory mechanics, including high tidal volumes, longer inspiratory times, and lower rates. This ventilator strategy enhances gas exchange, decreases the risk of atelectasis, decreases dead space ventilation, and can improve pulmonary vascular resistance. Moreover, it has also been shown to improve survival in patients with severe BPD [5–7]. The authors also inquired if any monitoring parameters were used to evaluate the changes in PEEP levels. All patients in the study were admitted to the neonatal intensive care unit (NICU), where monitoring of oxygen saturation and CO2 levels via end-tidal CO2 (EtCO2), transcutaneous CO2 (TcCO2), or blood gas analysis are standard of care. After optimization of ventilator settings, including PEEP oxygenation and ventilation parameters improved. For instance, in case number three, the EtCO2 levels decreased from 100 to 60 s (Fig. 1). In addition,