This review explains the principles of lung and diaphragm-protective mechanical ventilation. The overall aim of this approach is to limit the adverse effects of mechanical ventilation on the lung and the diaphragm at the same time. This requires understanding of the pathophysiology of ventilator-induced lung injury, critical illness-associated diaphragm weakness and especially respiratory drive. We discuss clinical applicable techniques to monitor lung and diaphragm function, and how to use these techniques to optimize ventilator settings and sedation. Future techniques that allow to control respiratory drive are discussed. |
Introduction
Principles and rationale
Principles of lung-protective ventilation
Principles of diaphragm-protective ventilation
Monitoring strategies
Parameter | Use | Advantages | Disadvantages | Suggested targets for lung and diaphragm-protective ventilation |
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Tidal volume (VT) | Indirect surrogate marker of risk of ventilator-induced lung injury Expired tidal volume may be used to detect volumes delivered above set volume in volume-controlled mode | Readily available | Strain is quantified by VT/EELV (end-expiratory lung volume), thus VT alone is not a precise measure of lung strain Does not reflect lung stress and does not correct for “baby lung” size | VT 4–8 ml/PBW |
Airway driving pressure (ΔPaw) | Monitor lung stress and strain resulting from inflation with tidal volume | Readily available | Does not reflect regional lung stress when respiratory effort is high Overestimates the transpulmonary pressure (PL) if chest wall elastance is increased and in the presence of expiratory muscle activity | ΔPaw < 15 cmH2O |
Paw and flow waveforms | Detect patient-ventilator dyssynchronies | Readily available Readily detects flow starvation, breath stacking, and premature cycling dyssynchronies | Some dyssynchronies may not be immediately evident without close inspection and additional monitoring of effort | Maintain patient-ventilator synchrony |
Airway occlusion pressure (P0.1) | Monitor respiratory drive and detect presence of low or high respiratory effort | Non-invasive Automated measurement available on most ventilators | Elevated respiratory drive does not always result in elevated respiratory effort (i.e., in the presence of respiratory muscle weakness or short inspiratory time) | P0.1 1–4 cmH2O |
Airway pressure swing during a whole breath occlusion (ΔPocc) | Assess for excessive respiratory effort and tidal lung stress | Non-invasive Easily measured at the bedside Can predict respiratory muscle effort (Pmus) and transpulmonary pressure swing (ΔPL,dyn) Detect apnea, auto-triggering Differentiate different forms of dyssynchrony | Though sensitive and specific for high respiratory effort and dynamic lung stress, the technique is not sufficiently accurate to replace direct measurement | Predicted Pmus 5–10 cmH2O (ΔPocc 8–20 cmH2O) Predicted ΔPL,dyn < 15–20 cmH2O |
Esophageal pressure (Pes) and transpulmonary pressure (PL) | Directly measure and monitor respiratory effort and tidal lung stress | Minimally invasive Provides gold standard information about lung stress (ΔPL) and respiratory effort (ΔPes, PTPes) | Requires equipment and training Balloon must be calibrated before each measurement Absolute values of Pes of unclear utility | ΔPes 3–15 cmH2O (diaphragm protective) ΔPL,dyn < 15–20 cmH2O (lung protective) |
Transdiaphragmatic pressure swing (ΔPdi) and gastric pressure swing (ΔPga) | Directly measure and monitor diaphragmatic effort and expiratory effort | Minimally invasive Provides direct measurement of diaphragmatic effort Provides information about expiratory muscle activity | Requires equipment and training Balloon must be calibrated before each measurement No calibration for Pga Difficult to assess post-inspiratory effort (eccentric loading) | ΔPdi–15 cmH2O |
Diaphragm inspiratory thickening fraction on ultrasound (TFdi) | Non-invasive assessment of diaphragmatic contractility | Provides an index of diaphragmatic effort during mechanical ventilation (tidal TFdi) Provides an index of diaphragmatic function (maximal TFdi) | Requires equipment and training Continuous monitoring is not feasible | TFdi 15–30% |
Diaphragm electrical activity (EAdi) | Monitor electrical activity of the diaphragm | Minimally invasive Continuous information with automated output Variation in EAdi correlates with variation in respiratory effort | Requires equipment and training No reference values | Normalize target EAdi based on Pocc, ΔPdi, or ΔPes |
Clinical strategies to facilitate lung and diaphragm-protective ventilation
Inspiratory ventilator settings
Expiratory ventilator settings
Resolving dyssynchrony
Sedation strategies
Drug class | Inspiratory effort and tidal volume | Respiratory rate | Ventilatory response to hypercapnia and hypoxemia | Effect on diaphragm function and patient-ventilator interaction |
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Benzodiazepines | ↓ | ⟷ or ↑ ↓ at high doses | ↓ | Delay restoration of diaphragm activity |
Propofol | ↓ | ⟷ or ↑ ↓ at high doses | ↓ | May ↑ dyssynchrony (i.e., ineffective efforts because of lower respiratory effort) |
Opioids | ⟷ or ↑ | ↓ | ↓ | May ↓ dyssynchrony (i.e., fewer ineffective efforts because of slower, deeper respiratory efforts) |
Dexmedetomidine | ⟷ | ⟷ | ⟷ | ↓ dyssynchrony by decreasing agitation/delirium |