Driving Pressures in a Closed-loop and a Conventional Mechanical Ventilation Mode

In 2015, Pediatric Acute Lung Injury Consensus Conference (PALICC) determined the pediatric acute respiratory distress syndrome (PARDS) definition. PALICC recommends using patient-specific tidal volume (VT) according to disease severity. Moreover, in the absence of transpulmonary pressure measurements (PL), an inspiratory plateau pressure limit of 28 cm H2O is recommended, allowing for slightly higher plateau pressures (29-32 cm H2O) for patients with reduced chest wall compliance. In adult ARDS, Amato et al. normalized VT to the compliance(C) by using driving pressure (ΔP) and reported that ΔP was the ventilation variable that best-stratified risk. Changes in ventilator settings resulting in a decrease in ΔP were associated with increased survival. One of the most common modes used in pediatric ventilation nowadays is synchronized controlled mandatory ventilation with adaptive pressure ventilation (APV-CMV). As compared to pressure control mode (P-CMV), APV-CMV prevents low or high VT when the compliance changes by adjusting the applied pressure. Adaptive support ventilation (ASV) is closed-loop ventilation mode, which for a given minute volume set by the clinician, adapts tidal volume (VT) and respiratory rate (RR) according to the patient's respiratory mechanics.

This prospective randomized cross over study aimed to compare ΔP between physician tailored APV-CMV mode and ASV 1.1 in pediatric mechanically ventilated patients with acute respiratory failure. After the enrollment, the patients' ventilation periods will be determined by randomization using sealed opaque envelopes. The minute ventilation, fraction of inspired O2 (FiO2) and positive end-expiratory pressure (PEEP) set by the clinician before study inclusion will be kept unchanged during all study periods. Patients will be ventilated in each mode for 60 minutes. Three consecutive -inspiratory and end-expiratory occlusion will be performed at 30 and 60 min and ΔP will be calculated for each period. Arterial blood gas will be measured at the end of each period. A wash-out period of 30 min using the ventilation mode and setting before inclusion will be performed in between the two study ventilation periods. ΔP will be calculated as the difference between plateau pressure (Pplat) and total PEEP and will be averaged for each ventilation period by using the mean of the six measurements mentioned above. VT will be calculated by integration of flow measurement. Resistance will be calculated by the least-squares fitting method. The expiratory time constant (RCexp) will be derived from the volume-flow curve at 75% of the VT and corresponding flow value. Static compliance (Cstat) will be calculated as VT divided by ΔP.

The primary outcome will be ΔP. The secondary outcome will be VT, RR, Pplat, Ti, Te, Cstat, Resistance, RCexp, pH, PaO2, PaCO2 A pilot study was performed to calculate the sample size. The mean ΔP was 12.4 (±3.31) cm H2O in ASV 1.1 and 13.5 (±4.2) cm H2O in APV-CMV. By using these pilot data, and assuming the power of 0.95 and α-error of 0.05, investigators have calculated the study size as 26 patients.

Inclusion criteria

• All the mechanically ventilated children
• between 1-months and 18-years-old
• without any detectable respiratory effort
• whose clinical condition are not foreseen to change within the next 3 hours

Exclusion criteria

• septic shock
• brain death diagnose,
• with a leak equal or more than 40% of the current VT,
• receiving extracorporeal membrane oxygenation (ECMO) or targeted temperature management (TTM),