Neural Pressure Support for Low Pulmonary Compliance

Acute respiratory failure (ARF) is a critical condition caused by impaired function of the lungs.1,2 The cornerstone of ARF management is invasive mechanical ventilation (IMV).3,4 Unfortunately, despite lifesaving, IMV is associated with several side effects (e.g., ventilator-associated pneumonia, ventilator associate induced lung injury, diaphragmatic dysfunction), and thus liberation from invasive mechanical ventilation is an everyday effort for critical care physicians.5

Pressure support ventilation (PSV) is one of the most widely used mechanical ventilation modes for liberation from IMV.6 PSV is a partial ventilatory mode: the ventilator and the patient co-operate to generate the inspiratory and expiratory pressures, flows, and volumes. During conventional PSV, the initiation of the breath is triggered by a reduction in expiratory pressure or a drop in expiratory flow.7 The termination of the breath occurs when the inspiratory flow falls to a predetermined fraction of the peak inspiratory flow.8

The main goal of mechanical ventilation is to help restore gas exchange and reduce the work of breathing (WOB) by assisting respiratory muscle activity.9 Knowing the determinants of WOB is essential for the effective use of mechanical ventilation and also to assess patient readiness for weaning. To reduce WOB, PSV needs to be synchronous and smooth interaction should happen between the ventilator and the respiratory muscles.10

Ideally, the ventilator trigger and cycling should coincide with the beginning and end of the patient's inspiratory effort.11 However, patient-ventilator asynchrony is common during PSV,12,13 thereby contributing to an increased work of breathing and an increased duration of mechanical ventilation.14

An important objective of assisted or patient-triggered mechanical ventilation is to avoid ventilator-induced diaphragmatic dysfunction by allowing the patient to generate spontaneous efforts.15 A second objective is to reduce the patient's work of breathing by delivering a sufficient level of ventilatory support.16 Finally, intuition suggests that a good match between patient respiratory efforts and ventilator breaths optimizes patient comfort and reduces work of breathing.17 Patient-ventilator asynchrony can be defined as a mismatch between the patient and ventilator inspiratory and expiratory times.18 Although inspiratory and expiratory delays are almost inevitable with most ventilatory modes, several patterns of major asynchrony exist and can be easily detected by clinicians.14