Lung protective ventilation is not a new concept in the world of mechanical ventilation. Extensive research has been published, and is continuing to be performed, to determine and confirm various mechanisms of lung injury. Diaphragm protective ventilation is relatively new concept in mechanical ventilation, with ongoing research looking at various mechanisms affecting this most important respiratory muscle. This article will aim to summarize the current state of lung protective ventilation, introduce diaphragm protective ventilation to those unfamiliar with it, and describe the various monitoring tools that can be incorporated into clinical practice to evaluate respiratory drive.
To describe the central ideas behind lung and diaphragm protective ventilation, we’ve invited Dr. Ewan Goligher to answer some these questions.
What would you consider the key elements of consideration for Lung Protective Ventilation?
The general concept of lung-protective ventilation is to minimize the stress and strain applied to the injured lung. The key lung-protective interventions—pressure and volume-limited ventilation, and prone positioning—work by decreasing stress and strain on the lung. Increasing PEEP may also have this benefit in patients with substantial potential for lung recruitment. So, behind all our efforts to protect the lung is the goal of minimizing stress and strain on the lung. The best available measure of lung stress and strain is the driving transpulmonary pressure, the pressure distending the lung with each tidal breath. The best available experimental and clinical evidence suggests that the tidal stretch (driving pressure) is more important than the peak stretch (plateau pressure), although both should be considered.
Monitoring Options for Lung Protective Ventilation
|Tidal volume (VT)||VT 4–8 ml/PBW|
|Airway driving pressure (ΔPaw)||ΔPaw < 15 cmH2O|
|Airway plateau pressure (Pplat)||≤ 28-30 cmH2O|
|Airway pressure swing during a whole breath occlusion (ΔPocc)||Predicted ΔPL,dyn < 15–20 cmH2O|
|Esophageal pressure (Pes) and transpulmonary pressure (PL)||ΔPL,dyn < 15–20 cmH2O (lung protective)|
What would you consider the key elements of consideration for Diaphragm Protective Ventilation?
To answer this question, we have to consider the type of injury you aim to protect against disuse atrophy, or injury due to excessive effort. The strongest evidence we have on this subject is in the area of disuse atrophy. Simply stated, if the diaphragm is not being used, atrophy occurs quickly in mechanically ventilated patients. However, growing evidence suggests that excessive diaphragm activity (loading) can cause diaphragm injury, potentially leading to diaphragm weakness and clinical complications such as increased time on the ventilator.
If you had an extremely complicated patient in which keeping all elements of Lung Protective Ventilation within acceptable range is difficult, what would be the TWO most important elements of Lung Protective Ventilation you would consider?
I’d argue that the two key elements of lung-protective ventilation are limiting tidal stress and limiting peak stress. Accordingly, both driving and plateau pressures should be the primary focus in these complicated patients.
We are often taught the benefits of spontaneous breathing during mechanical ventilation. How could respiratory effort contribute to lung injury during invasive mechanical ventilation?
Again, the basic issue is lung stress and strain. Just as a ventilator applies pressure to the lung, the respiratory muscle contractile force applies pressure to the lung as it inflates. The challenge for clinicians is that our traditional monitoring strategies do not allow us to “see” the effect of respiratory muscle effort on lung stress—we do not assess the pressure on the lung generated by the muscles. Consequently, respiratory muscle effort during spontaneous breathing can substantially increase lung stress and strain without an obvious increase in airway pressures. Recent papers have demonstrated that plateau pressure can provide an accurate measure of peak lung stress in many patients on assisted ventilation, so it’s possible to measure the driving pressure and plateau pressure resulting from both the ventilator-delivered pressure and the respiratory muscle pressure. However, given the regional variation in force generation in patients with spontaneous breathing and severe lung injury, these usual measurements can seriously underestimate regional lung stress and strain. Regional imaging techniques like EIT are required to detect this. Essentially, excessive respiratory muscle effort should be avoided to protect the lung from injury.
Common Monitoring Options for Patient Effort
|Airway occlusion pressure P0.1||1 to 4 cmH2O (-1 to -4 depending how ventilator displays the value)|
|Airway pressure swing during a whole breath occlusion (ΔPocc)||Predicted Pmus 5–10 cmH2O (ΔPocc 8–20 cmH2O)|
|Esophageal pressure (Pes) and transpulmonary pressure (PL)||ΔPes 3–15 cmH2O (diaphragm protective)|
|Diaphragm inspiratory thickening fraction on ultrasound (TFdi)||TFdi 15–30%|
What are some clinical strategies that can be attempted to try and maintain an acceptable range of inspiratory effort?
Clinicians should individualize ventilator settings to ensure patient interaction is optimal (synchronous), this can be done through adjustments of flow, inspiratory time, or cycle % (for example) depending on the mode being used. Ensuring oxygenation is adequate and PEEP is not insufficient or excessive (a challenge itself). Finally, the choice of sedation (and its dose) should focus on effort reduction without impacting respiratory rate.
Ideally, we would like preserve diaphragm function while protecting the lung during invasive mechanical ventilation. If this could not be accomplished, would one (lung or diaphragm) take priority over the other?
The amount of data supporting the benefits of lung protective ventilation certainly outweigh the data supporting a diaphragm protective strategy. Currently, the lung would take priority. Further research is needed to confirm how these two concepts can be managed together.
Goligher, E.C., Jonkman, A.H., Dianti, J. et al. Clinical strategies for implementing lung and diaphragm-protective ventilation: avoiding insufficient and excessive effort. Intensive Care Med 46, 2314–2326 (2020). https://doi.org/10.1007/s00134-020-06288-9