NAVA Unloading - Effects on Distribution of Ventilation

Study Overview
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Brief Summary
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Title: Reduced Unloading in NAVA Improves distribution of Ventilation in ICU patients. Objectives: To investigate if NAVA targeted to moderate respiratory muscular unloading results in redistribution of ventilation to the dorsal regions of the lungs To verify if the redistribution of ventilation translates to a better gas exchange and to a potentially lung protective ventilation strategy (lower airway pressures) To verify the possibility to set NAVA at different levels of unloading, based on Neuro-Ventilatory Efficiency. Study Design: Randomised Crossover of Pressure Support and NAVA at different levels of unloading. Population: Adult Intubated patients at the Neurosurgical ICU, ventilated for more than 48h, in weaning phase from mechanical ventilation. Study duration: 2,5h Number of subjects: 12

Detailed Description
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Critically ill patients on mechanical ventilation are at risk for developing respiratory muscle atrophy. Partial Assist modes such Pressure Support (PS) and Neurally Adjusted Ventilatory Assist (NAVA) are developed to maintain patients´own effort in breathing. However there are no recommendations on how to set the optimal ventilator support in NAVA to avoid over- or underassistance. A previous Electrical Impedance Thomography (EIT) study has shown a redistribution of ventilation towards the dorsal regions of the lung in acute lung injury patients ventilated with NAVA, compared to PS. In the present study, the assist is targeted to different respiratory muscle unloading, predefined and based on the Neuro-Ventilatory Efficiency (NVE). The NVE will be measured at 10min intervals and NAVA level adjusted if needed, to keep constant the level of unloading in each study step. Protocol: Once enrolled, the patients are ventilated in PS (PScli1) as set by the clinician. They are then ventilated in NAVA at 3 different levels of muscle unloading in randomized order. At NAVAcli, the assist level matches to PScli1 in terms of muscle unloading. With NAVA40% and NAVA60%, the patients have 40% and 60% unloading, respectively. In the last study step the patients are back to PS (PScli2). Each patient is his/her own control and goes through the 5 ventilation periods, of 30min each. In the last 5 min of each study step, the CoV (obtained through the EIT data), blood gas samples (for oxygenation and ventilation) and ventilatory parameters are obtained and analyzed. The investigators hypothesize that It is possible to set NAVA at different levels of unloading, based on NVE. Moderate muscle unloading (corresponding to NAVA40%) keeps the diaphragm active and thereby leads to more dorsal distribution of ventilation compared to PScli and to higher unloading in NAVA. Secondarily and as a consequence of the redistribution of ventilation, we hypothesize that the gas exchange will remain unchanged or will improve and that the airway pressures will decrease for moderate unloading (NAVA40%).

Official Title
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Reduced Unloading in NAVA Improves Distribution of Ventilation in ICU Patients

Conditions
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Acute Respiratory Failure

Intervention / Treatment
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* Device: Neurally adjusted ventilatory assist
* Device: PScli1
* Device: PScli2


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Patients belonging to Neurosurgical ICU Intubated for ≥48h Weaning phase from Mechanical Ventilation Exclusion Criteria: bleeding disorders (PK INR>1,5 or APTT>50s or platelet count <50000/µL) or unstable intracranial pressure (ICP>20 mmHg during the latest 8 hours) or unstable circulation (requiring high vasopressor dose, for example Noradrenalin >0,2µg/kg/min) or too severe lung disease (PFI ≤ 26,7 kPa or PEEP >10 cmH2O or FiO2>0,5 at study entry point) or fever> 38,5°C or tendency to hyperventilation (PaCO2 < 4,5 kPa at study entry point).

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Supportive Care
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: PScli1<br>Patients are ventilated in Pressure support (PS) according to the Clinical settings for 30min. | Device: PScli1<br>* Pressure support set by clinicians prior to inclusion<br>* Other names: Pressure support;|
| Active Comparator: NAVAcli<br>Patients are ventilated in Neurally Adjusted Ventilatory Assist (NAVA) and the assist is set in order to match to respiratory muscle unloading reached with PScli1. Patients are ventilated in NAVAcli for 30min. | Device: Neurally adjusted ventilatory assist<br>* Ventilation supported by NAVA Blood gas analysis Respiratory Parameters At the end of the study step Neuro-Ventilatory Efficiency and Neuro-Mechanical Efficiency are measured.<br>* Other names: NAVA;|
| Active Comparator: NAVA40%<br>Patients are ventilated in Neurally Adjusted Ventilatory Assist (NAVA) and the assist is set in order to target 40% muscle unloading based on the Neuro-Ventilatory Efficiency (NVE) measurement. Patients are ventilated in NAVA40% for 30min. | Device: Neurally adjusted ventilatory assist<br>* Ventilation supported by NAVA Blood gas analysis Respiratory Parameters At the end of the study step Neuro-Ventilatory Efficiency and Neuro-Mechanical Efficiency are measured.<br>* Other names: NAVA;|
| Active Comparator: NAVA60%<br>Patients are ventilated in Neurally Adjusted Ventilatory Assist (NAVA) and the assist is set in order to target 60% muscle unloading based on the Neuro-Ventilatory Efficiency (NVE) measurement. Patients are ventilated in NAVA60% for 30min. | Device: Neurally adjusted ventilatory assist<br>* Ventilation supported by NAVA Blood gas analysis Respiratory Parameters At the end of the study step Neuro-Ventilatory Efficiency and Neuro-Mechanical Efficiency are measured.<br>* Other names: NAVA;|
| Active Comparator: PScli2<br>Patients return to PS ventilation, according to the Clinical settings as in PScli1 for 30min. | Device: PScli2<br>* Pressure support at the same level as prior to the study<br>* Other names: Pressure support;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Center of Ventilation (CoV), expressed in percent (ventral to dorsal) | The distribution of ventilation is summarized by the CoV, a parameter obtained by the EIT monitor. Recordings are made at the end of each study step (total 5), lasting 30min. | Total study time is 2,5 hours | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Gas Exchange (PaO2 and PaCO2) | Comparison between study steps | During the last 5min of each study step (each 30min), total 5 steps. Total study time 2,5 hours | 
| Airway Pressure |  | 2,5 hours | 
| Muscle unloading based on Neuro-Ventilatory Efficiency and Neuro-Mechanica Efficiency |  | 2,5 hours | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Neurally adjusted ventilatory assist