Clinical review: Patient-ventilator interaction in chronic obstructive pulmonary disease

In patients with chronic obstructive pulmonary disease (COPD), mechanical ventilation, both invasive (MV) and noninvasive (NIV), often proves challenging due to the interaction between the various pathophysiological mechanisms of the disease and the goals of ventilatory support [1,2]. Thanks to increased knowledge gained over the years, the severe complications associated with dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEPi) [3], first described over 20 years ago [4], have become less frequent [2,3]. However, some aspects of MV in these patients remain very difficult to manage, in particular patient-ventilator interaction, that is, the combination of the patient's spontaneous breathing activity and the ventilator's set parameters [5,6]. Further complicating the matter, during NIV, leaks at the patient-mask interface can interfere with various aspects of ventilator function, thereby increasing the risk of patient-ventilator asynchrony [7-10].Overall, whereas the goal of ventilatory support is to provide some degree of unloading to the respiratory muscles, the opposite effect can occur if the patient and the ventilator engage in a tug-of-war between conflicting goals rather than sharing the respiratory workload, which can in turn lead to failure of NIV or the prolonged need for MV [5,6].The purpose of this paper is to review the basic mechanisms involved in patient-ventilator interaction in COPD patients, and to outline some of the possible paths towards improving this often difficult relationship.In a spontaneously breathing subject, the pressure generated by the respiratory muscles (Pmus) during inspiration is dissipated to overcome both the elastic and resistive forces opposing respiratory system inflation, as described by the equation of motion of the respiratory system:Pmus = (Rrs × V') + (Ers × V) (equation 1)where Ers is respiratory system elastance, Rrs is respiratory system resistance, V' is inspiratory flow, and V is volume of th