Acceptable Range of Inspiratory Effort During Mechanical Ventilation

Study Overview
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Brief Summary
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Partially assisted mechanical ventilation is ideally titrated to maintain adequate inspiratory muscle activity (i.e. preventing disuse atrophy) while avoiding excessive (i.e. fatiguing) inspiratory loads. The advent of ventilator modes enabling flow and pressure assistance in proportion to patient inspiratory effort (i.e. Proportional Assist Ventilation (PAV), Neurally-Adjusted Ventilator Assist (NAVA)) permit careful titration of ventilatory support to achieve desired levels of patient inspiratory effort. However, data on the acceptable range of values for inspiratory effort and respiratory muscle load-capacity balance during mechanical ventilation are currently very limited. Such data are critical to inform a physiologically sound evidence-based approach to titrating partially-assisted ventilatory support. This study is designed to ascertain a physiologically acceptable range of inspiratory effort in mechanically ventilated patients. The study protocol includes measurements of the respiratory system during spontaneous breathing as well as evaluating the diaphragm in real-time with the use of ultrasonography. The experimental design outlined in the present study is predicated on the assumption that the range of values for inspiratory effort and load-capacity balance observed in patients who are successfully weaned from mechanical ventilation represent the safe and appropriate range of target values.

Conditions
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Elective Cardiac Surgery

Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: - Adult patients (>17) receiving invasive mechanical ventilation following elective cardiac surgery who will undergo a trial of spontaneous breathing Exclusion Criteria: Pregnant women Decompensated cardiac insufficiency or acute coronary syndrome Severe COPD Contraindications to esophageal catheter placement, namely known esophageal varices

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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What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Maximal inspiratory effort generated by a patient |  | During 10-15 minutes of the spontaneous breathing trial | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Diaphragmatic thickening fraction |  | 15 minutes | 
| Diaphragmatic excursion |  | 15 minutes | 
| Success or failure of the spontaneous breathing trial |  | 15 minutes | 
| Muscular load-capacity balance measured by the tension-time index of the respiratory muscles |  | 15 minutes | 
| Airway occlusion pressure (P0.1) performed manually and as measured by the ventilator |  | 15 minutes | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Spontaneous Breathing Trial, Inspiratory Effort, Mechanical Ventilation, Respiratory muscle load-capacity balance