Patient-Ventilator Interaction: Timing Discordance in Invasive Ventilation

Mechanical ventilation goals include restoration of gas exchange, lung protection, and patient comfort. Improving patient comfort through synchronous patient-ventilator interaction represents a common clinical challenge in the management of these patients. Patient-ventilator discordance describes a mismatch between the patient's intrinsic respiratory timing and effort with the ventilatory support provided by the ventilator. Achieving concordance requires an understanding of physiologic principles related to the control of breathing, expertise in recognition of discordance using the pressure and flow waveforms, and an in-depth knowledge of ventilator operation. Discordance is a common occurrence in ventilated patients, and over the past two decades, the recognition of patient-ventilator discordance has improved with education, simulation, and advances in instrumentation. Despite these advances, the impact of patient-ventilator discordance remains controversial. Growing evidence suggests patient-ventilator discordance is associated with adverse outcomes including mortality, increased sedation requirements, and duration of mechanical ventilation, although a cause-and-effect relationship has not been clearly demonstrated. Discordance may simply be a marker of the severity of illness. However, the impact of discordance varies based on the type and timing of discordance, lung mechanics, and the magnitude of patient effort. Some types of discordance may have positive effects. This article aims to explore the pathophysiology and identification of patient-ventilator discordance related to timing.