Impact of Proportional Assisted Ventilation on Dyspnea and Asynchrony in Mechanically Ventilated Patients

Rational As opposed to controlled mechanical ventilation, partial modes of assisted ventilation maintains a certain level spontaneous activity of respiratory muscles. As a consequence, assisted ventilation may contribute to prevents ventilator induced diaphragm dysfunction (1-3), improves gas exchanges (4), reduces the use of sedative agents, which can ultimately shorten weaning from mechanical ventilation (5).

The most widely used partial ventilatory assistance mode is pressure support ventilation (PSV) (6), in which a constant preset level of pressure assists each inspiration regardless of the patient's inspiratory effort. Mismatching between patient demand and level of assistance, which the investigators will term patient-ventilator dysharmony in the present project is therefore possible and can be potentially harmful. On the one hand, underassistance may induce respiratory discomfort and dyspnea (7), which is an immediate cause of suffering, generates anxiety and is a source of delayed neuropsychological sequelae such as dark respiratory recollections and post-traumatic stress disorders(8-12). One the other hand, overassistance may cause lung overdistension and volutrauma (13). Finally, both underassistance and overassistance may generate patient-ventilator asynchrony that is associated with poorer clinical outcomes (14). Of notice, underassistance is likely to be associated with an asynchrony named double-triggering while over assistance is more commonly associated with ineffective efforts(15).

Proportional modes of mechanical ventilation have been designed to overcome this weakness of (PSV). Indeed, as opposed to PSV that delivers a constant level of assistance regardless of the patient inspiratory effort, proportional modes of ventilation adjust the amount of assistance delivered with respect to the patient's efforts. Proportional Assisted Ventilation (PAV) is one of these modes and adjusts ventilator assistance to the activity of respiratory muscles estimated by an algorithm (16-23). Previous studies have shown the potential benefits of PAV to prevent the risk of overassistance(24) and in turn to reduce the prevalence of ineffective effort (25-28). In addition, PAV increases the variability of the breathing pattern (17, 20-23, 29-32). To date, data on the impact of PAV on dyspnea and patient ventilator asynchrony are scarce (24-28, 33). Most of these works have been conducted in healthy subjects or in ICU patients with no severe dyspnea nor severe asynchrony (24-28, 33). To our knowledge, there are no data in patients with severe patient-ventilator dysharmony.

Because PAV adjusts the level of assistance to the activity of respiratory muscles, a surrogate of the respiratory drive, it is licit to hypothesize that PAV should prevent severe patient-ventilator dysharmony, defined as either severe dyspnea or severe patient-ventilator asynchrony.

The objective of the present research proposal is to evaluate the impact of PAV on dyspnea and patient-ventilator asynchrony in ICU mechanically ventilated patients in intensive care with severe patient-ventilator disharmony defined as either severe dyspnea or severe patient-ventilator asynchrony.