Real-time Effort Driven VENTilator Management

Ventilation Therapy; Complications, Diaphragm Disease, Pediatric Respiratory Diseases

This study is a Phase II controlled clinical trial that will obtain comprehensive, serial assessments of respiratory muscle strength and architecture to understand the evolution of ventilator-induced respiratory muscle weakness in critically ill children, and test whether a novel computer-based approach (Real-time Effort Driven ventilator management (REDvent)) can preserve respiratory muscle strength and reduce time on MV. REDvent offers systematic recommendations to reduce controlled ventilation during the acute phase of MV, and uses real-time measures from esophageal manometry to adjust supported ventilator pressures such that patient effort of breathing remains in a normal range during the ventilator weaning phase. This phase II clinical trial is expected to enroll 276 children with pulmonary parenchymal disease, anticipated to be ventilated \> 48 hrs. Patients will be randomized to REDvent-acute vs. usual care for the acute phase of MV (interval from intubation to first spontaneous breathing trial (SBT)). Patients in either group who fail their first Spontaneous Breathing Trial (SBT), will also be randomized to REDvent-weaning vs. usual care for the weaning phase of MV (interval from first SBT to passing SBT). The primary clinical outcome is length of weaning (time from first SBT until successful passage of an SBT or extubation (whichever comes first)). Mechanistic outcomes surround multi-modal serial measures of respiratory muscle capacity (PiMax), load (resistance, compliance), effort (esophageal manometry), and architecture (ultrasound) throughout the course of MV. Upon completion, this study will provide important information on the pathogenesis and timing of respiratory muscle weakness during MV in children and whether this weakness can be mitigated by promoting more normal patient effort during MV via the use of REDvent. This will form the basis for a larger, Phase III multi-center study, powered for key clinical outcomes such as 28-day Ventilator Free Days.

Study Aims: SA1: To determine if REDvent acute and/or weaning phase protocols can shorten the duration of weaning from MV (Primary outcome). SA2: To determine if changes to direct measures of respiratory muscle strength, load, effort, and architecture throughout the duration of MV are related to weaning outcomes. SA3: To determine if patient effort of breathing during both acute and weaning phases of MV is independently associated with the development of respiratory muscle weakness. Study Design: Single-center randomized controlled trial (138 children per arm) using REDvent (intervention arm) as compared with usual care ventilator management including a standardized daily SBT (control arm). Acute phase randomization will occur upon study enrollment, and patients who fail the first SBT will undergo a weaning phase randomization. The investigators will obtain serial measurements of respiratory system capacity, load, effort of breathing, and diaphragm architecture throughout the course of MV. Acute Phase: The acute phase is defined as the time from intubation until the patient meets weaning criteria, passes the initial oxygenation test (decrease PEEP to 5 cmH2O and FiO2 to 0.5, maintains SpO2 \> 90%), and undergoes a Spontaneous Breathing Trial (SBT). 1. Intervention Arm (REDvent-acute): Patients will be managed with pressure control plus pressure support ventilation using a computerized decision support tool that will recommend changes to ventilator settings approximately every 4 hr (with or without a new blood gas). If the patient is spontaneously breathing, it will incorporate real-time measures of effort of breathing (esophageal manometry) to keep it in a target range. 2. Control Arm (Control-acute): Ventilator management will be per usual care until the patient meets weaning criteria and passes the oxygenation test. Weaning Phase: The weaning phase is defined as the time from the first Spontaneous Breathing Trial (SBT) until the patient successfully passes an SBT or is extubated (whichever comes first). Patients who pass the initial SBT at the end of the acute phase will not undergo weaning phase randomization. 1. Intervention Arm (REDvent-weaning): Patients will be managed in a pressure support/CPAP mode of ventilation with assessments or changes to the level of pressure support every 4 hours, targeting maintaining effort of breathing (esophageal manometry) in a normal range. An SBT will be conducted daily, and the weaning phase will continue until the patient passes the SBT. 2. Control Arm (Control-weaning): Ventilator management will be per usual care. An SBT will be conducted daily, and the weaning phase will continue until the patient passes the SBT. Analysis Plan and Sample Size Justification: Aim 1: The primary outcome is weaning duration. Sample size has been determined to adequately power 3 separate comparative analyses: (a) REDvent-acute versus Acute Phase control (b) REDvent-weaning phase versus Weaning Phase control (c) REDvent both phases versus control both phases. Power is based on 2 planned methods for analysis: cox proportional hazard ratios for multivariable analysis and univariate analysis with an independent t-test using log transformation (as needed) to account for the expected distribution of weaning duration. For all three of the planned comparisons above, with the proposed sample size the investigators would be adequately powered (\>0.8) to detect a difference in weaning duration of ≥ 1 day, or a hazard ratio of ≥ 1.4 between groups. The secondary outcomes are ventilator free days and extubation failure. Directly comparing control only patients to REDvent only patients, with an expected standard deviation for VFDs between 5 to 9 days, the investigators will be able to detect a 2-day change in VFDs between groups with a power between 0.35 and 0.82. Re-intubation rates are expected to be 10%, allowing the investigators to confirm that REDvent is not inferior to usual care in regards to re-intubation with a non-inferiority margin of 0.10 with a power of 0.8 and alpha of 0.05. Aim 2: The primary outcome of this aim is weaning duration. For respiratory muscle strength the investigators will compare the first measured aPiMax (after resolution of the acute phase, before the first SBT), the trajectory and value of the daily aPiMax during the weaning phase prior to extubation, the lowest and highest measured aPiMax, and aPiMax on the day of extubation against weaning duration. For analysis, aPiMax will be dichotomized at 30 cmH2O, and weaning duration will be compared between patients with aPiMax \> 30 versus ≤ 30 cmH2O using a t-test with or without log-transformation, or Mann-Whitney U test, depending on the distribution. From preliminary data, it is anticipated at least 35% of patients (n=84) will have aPiMax ≤ 30 cmH2O. Based on a similar power analysis as presented above, this would allow the investigators to determine whether low aPiMax is associated with a ≥ 1-day increase in weaning duration, with an alpha of 0.05 and power of 0.8. The investigators will perform identical analysis for ePiMax. Diaphragm Thickness analysis will compound daily ultrasound measures to detect the relative change in diaphragm thickness from study day 1 until passage of an SBT. The investigators will compare the change in thickness after resolution of the acute phase (on the day of the first SBT) against weaning duration, in a similar manner as proposed above for aPiMax. In addition to weaning duration, the investigators will also examine whether the respiratory measures taken just prior to or during each SBT are associated with the patient passing the SBT. For example with aPiMax and ePiMax, the investigators will examine if there is a dose response relationship between PiMax measured just before the SBT and the rate of passage of the subsequent SBT. Aim 3: The primary outcome of this aim is aPiMax \< 30 cmH2O.The analysis will focus on determining whether the degree of patient effort of breathing is independently associated with the development of respiratory muscle weakness. For the acute phase, the investigators will generate a time-weighted average PRP during the acute phase and graph it against aPiMax at the first SBT. They will subsequently dichotomize aPiMax at the first SBT and compare mean time weighted average PRP in the acute phase between aPiMax groups (\> 30 vs. ≤ 30 cmH2O). For the weaning phase, the investigators will graph the changes in aPiMax throughout the weaning phase (from first failed SBT until successful SBT) against time-weighted average PRP, with the anticipation that low PRP will be associated with either further reductions in aPiMax, or no improvement, while PRP in the physiologic range of 150-400 will be associated with improvement in aPiMax. The investigators will subsequently dichotomize aPiMax (at 30 cm H2O) at the time of successful passage of an SBT and compare time-weighted average PRP in the weaning phase between aPiMax groups. Subsequently, the investigators will build a multivariable logistic regression model on the outcome of aPiMax ≤ 30 cmH2O to determine if time-weighted PRP in the acute phase, weaning phase or both have an independent association with preserving aPiMax, after controlling for confounding variables.

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