The goal of this interventional study is to evaluate the effect of different positive end-expiratory pressures (PEEP) on lung and diaphragm function in patients mechanically ventilated with pressure support ventilation in the intensive care unit. The main questions aim to answer:
Does higher PEEP level affect diaphragm contractions and ventilatory efficiency? Does higher PEEP level limit inspiratory efforts? Does higher PEEP level affect lung compliance?
The participants will be subjected to three different PEEP levels during pressure support ventilation:
Low PEEP (4 cmH2O), Medium PEEP (10 cmH2O), High PEEP (16 cmH2O).
The lung and diaphragm function will be evaluated using high-resolution esophageal manometry, electrical activity of the diaphragm, external diaphragm ultrasound and spirometric ventilator data.
Mechanical ventilation with pressure support or mechanical ventilation with possibility to transition to pressure support
Oxygen requirement ≤ 50%
Pressure support ≤ 12 cmH2O
PEEP ≤ 12 cmH2O
Circulatory instability
Brain death diagnosis/brain death evaluation
Norepinephrine dose > 0.4 µg/kg/min
Muscle relaxation administered within 2 hours
Crossover
Low positive end-expiratory pressure
Procedure/SurgeryLow (4 cmH2O) positive end-expiratory pressure (PEEP) will be applied during pressure support ventilation. The PEEP level will be kept for 10 minutes prior to data acquisition.
Medium positive end-expiratory pressure
Procedure/SurgeryMedium (10 cmH2O) positive end-expiratory pressure (PEEP) will be applied during pressure support ventilation. The PEEP level will be kept for 10 minutes prior to data acquisition.
High positive end-expiratory pressure
Procedure/SurgeryHigh(16 cmH2O) positive end-expiratory pressure (PEEP) will be applied during pressure support ventilation. The PEEP level will be kept for 10 minutes prior to data acquisition.
Inspiratory effort
Inspiratory effort will be measured by the tidal change in esophageal pressure (in cmH2O) during assisted breathing. The esophageal pressure will be measured using a high-resolution manometry catheter. The change from expiratory to inspiratory esophageal pressure will represent the tidal change and be used to estimate the inspiratory effort.
Inspiratory drive
The electric activity of the diaphragm (Eadi) will be measured using a NAVA (neurally adjusted ventilatory assist) catheter. The change from end-expiratory to inspiratory Eadi will be calculated. This represents the inspiratory drive. The Eadi will be measured in Voltage.
Effort-to-drive ratio
The effort-to-drive ratio (EDR) will be calculated as the inspiratory effort (tidal change in esophageal pressure) divided by the inspiratory drive (tidal change in electric activity of the diaphragm).
Neuromechanical efficiency
The neuromechanical efficiency will be calculated as the change in airway pressure during an occlusion test (Pocc) (measured from end-expiration to maximum negative pressure during the occlusion manoeuvre) divided by the inspiratory change in electric activity of the diaphragm (from end-expiration to inspiration).
Airway driving pressure
Difference in airway pressure between end-expiration and during an inspiratory hold will be calculated from the ventilator data.
Lung compliance
Lung compliance will be calculated as the tidal volume divided by the change in transpulmonary pressure from end-expiration to end-inspiration.
Thickening fraction of the expiratory abdominal muscles (TFabd)
The abdominal muscles will be visualized by ultrasound in the anterior axillary line, midway between the inferior border of the ribcage and the iliac crest. The thickening fraction will be calculated as \[(expiratory thickness - end-inspiratory thickness) / end-inspiratory thickness \].
Oxygenation
The PFI (PaO2/FiO2 ratio) will be calculated as arterial PaO2 (partial pressure of oxygen) divided by the FiO2 (fraction of inspired oxygen)
Central venous oxygen saturation (ScvO2)
Oxygen saturation of venous blood drawn from a central venous catheter.
Tidal volume
The volume change from end-expiration to end-inspiration. Will be acquired from the ventilator.
Respiratory rate
The number of breaths per minutes (respiratory rate) will be calculated from the volume-time curve acquired from the ventilator.
Dead space
Dead space (volume of gas not participating in gas exchange) will be calculated from the difference between arterial and end-expiratory partial pressure of Carbon dioxide, using blood gas analysis and capnography.
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Vastra Gotaland Region
Lead sponsor
Sahlgrenska University Hospital
Collaborator
Göteborg University
Collaborator
