Interactions patient-ventilateur en aide inspiratoire

Pressure support is a ventilatory mode which theoretically provides pressurization in synchrony with the patient's inspiratory efforts. However, asynchrony can occur in the presence of altered respiratory mechanics, particularly in obstructive patients. Patient-ventilator asynchrony can manifest itself through signs of respiratory distress during mechanical ventilation, but also, more insidiously, by the presence of ineffective inspiratory attempts, resulting from dynamic hyperinflation due to obstructive airways disease. Severe and prolonged asynchrony is associated with poor outcome. Improving patient-ventilator interactions requires thorough knowledge of the pathophysiological mechanisms involved in the various phases of the respiratory cycle: triggering of the ventilator, pressurization, transition from inspiration to expiration (cycling), and expiration. Understanding the mechanisms present during each phase allows the clinician to optimize the various settings of this mode: level of pressure support, pressurization slope, positive end expiratory pressure, and cycling set point. During non invasive ventilation, leaks can further complicate this difficult process, but the added effort is certainly justified, given the favourable prognostic impact of avoiding intubation.