Dissipated Energy is a Key Mediator of VILI: Rationale for Using Low Driving Pressures

Abstract

Positive pressure ventilation should never be seen as a simple and safe intervention, either in patients under general anesthesia for surgery in whom ventilation usually lasts minutes to hours, or in critically ill patients who generally need invasive ventilation for days to weeks. Indeed, positive pressure ventilation is increasingly recognized as a potentially harmful intervention, with ventilator-induced lung injury (VILI) as one of its most important adverse-effects [1]. So-called ‘lungprotective’ ventilation strategies, i.e., ventilation strategies aiming at prevention of VILI, have a strong potential to benefit patients with acute respiratory distress syndrome (ARDS) as well as patients with uninjured lungs [2].

What is the best way to protect the lungs during positive pressure ventilation? Should ‘lung-protective’ mechanical ventilation always include the use of low tidal volumes, because clinical studies showed that tidal volume restriction improved outcome of ARDS patients [3, 4] and suggested benefit in patients with uninjured lungs [5–7]? And should it always include higher levels of positive end-expiratory pressure (PEEP), because PEEP up-titration has been shown to improve outcome of ARDS patients [8]?

Recently, another ventilator setting has been suggested that could reduce harm from positive pressure ventilation. In a large cohort of patients with ARDS the “driving pressure”, defined as the plateau pressure or its equivalent minus the level of PEEP, appeared to be strongly and independently associated with mortality [9]. This review focuses on the interaction between energy dissipated in the lung during positive pressure ventilation as a rationale for aiming for the lowest driving pressure by manipulating tidal volume size and the level of PEEP in individual patients.