Lung- and Diaphragm-Protective Ventilation

Abstract

Mechanical ventilation can cause acute diaphragm atrophy and injury, and this is associated with poor clinical outcomes. Although the importance and impact of lung-protective ventilation is widely appreciated and well established, the concept of diaphragm-protective ventilation has recently emerged as a potential complementary therapeutic strategy. This Perspective, developed from discussions at a meeting of international experts convened by PLUG (the Pleural Pressure Working Group) of the European Society of Intensive Care Medicine, outlines a conceptual framework for an integrated lung- and diaphragm-protective approach to mechanical ventilation on the basis of growing evidence about mechanisms of injury. We propose targets for diaphragm protection based on respiratory effort and patient-ventilator synchrony. The potential for conflict between diaphragm protection and lung protection under certain conditions is discussed; we emphasize that when conflicts arise, lung protection must be prioritized over diaphragm protection. Monitoring respiratory effort is essential to concomitantly protect both the diaphragm and the lung during mechanical ventilation. To implement lung- and diaphragm-protective ventilation, new approaches to monitoring, to setting the ventilator, and to titrating sedation will be required. Adjunctive interventions, including extracorporeal life support techniques, phrenic nerve stimulation, and clinical decision-support systems, may also play an important role in selected patients in the future. Evaluating the clinical impact of this new paradigm will be challenging, owing to the complexity of the intervention. The concept of lung- and diaphragm-protective ventilation presents a new opportunity to potentially improve clinical outcomes for critically ill patients.

Keywords: artificial respiration; lung injury; mechanical ventilation; myotrauma.

Figure 1.

Mechanisms of injury to the lung and diaphragm during mechanical ventilation. Ventilator settings and sedation exert complex and interacting effects on the mechanisms of lung and diaphragm injury. Reducing ventilator-applied pressures may fail to protect the lung because of a resultant increase in respiratory effort when respiratory drive is intact. Suppressing respiratory drive to protect the lung by increasing sedation can lead to disuse diaphragm atrophy. Conversely, maintaining respiratory drive to avoid diaphragm atrophy may result in patient self-inflicted lung injury and load-induced diaphragm injury if respiratory effort is excessive. Thus, a careful balancing act between excessive and insufficient ventilation and sedation may be required to protect both the lung and the diaphragm concomitantly. Similarly, positive end-expiratory pressure (PEEP) can exert complex and competing effects on the mechanisms of injury, and all of these effects may need to be considered when setting PEEP in individual patients. The risk of injury to the lung and diaphragm is likely “dose dependent”—the injury risk depends on the magnitude of stress and strain in the baby lung and the magnitude of respiratory efforts generated during assisted breaths and asynchronies. P-SILI = patient self-inflicted lung injury; VILI = ventilator-induced lung injury.

Figure 2.

Monitoring strategies for lung- and diaphragm-protective ventilation. These tracings illustrate the utility of semiinvasive monitoring by esophageal manometry and noninvasive monitoring strategies using respiratory maneuvers on the ventilator. Esophageal pressure (Pes) swings (ΔPes) reflect patient respiratory effort. Transpulmonary pressure (Pl) swings (ΔPl,dyn; the difference between airway pressure [Paw] and Pes) directly assess dynamic lung stress. Driving Paw (ΔPaw) and transpulmonary driving pressure (ΔPl) can be quantified even when patients make spontaneous respiratory efforts by applying an end-inspiratory occlusion to measuring plateau pressure (Pplat). Pplat may be higher than peak Paw when patients make spontaneous respiratory efforts (as shown) because the lung is inflated by respiratory muscle effort as well as positive pressure from the ventilator. The Paw swing during Pocc can be used to predict both ΔPl,dyn and respiratory effort (53). Airway occlusion pressure (P_0.1) can be used to detect insufficient or excessive respiratory drive. Pocc = expiratory occlusion pressure.

Figure 3.

Conceptual framework for lung- and diaphragm-protective ventilation. Major goals (homeostasis, lung protection, and diaphragm protection) are achieved by delivering mechanical ventilation according to proposed therapeutic targets. The goal of the strategy is not primarily to restore normal physiology but to minimize injury and optimize patient outcomes. QOL = quality of life.