Go with the flow—clinical importance of flow curves during mechanical ventilation: A narrative review

Abstract

Most clinicians pay attention to tidal volume and airway pressures and their curves during mechanical ventilation. On the other hand, inspiratory-expiratory flow curves also provide a plethora of information, but much less attention is paid to them. Flow curves chronologically show the velocity and direction of inspiration and expiration and are influenced by the respiratory mechanics, the patient's effort, and the mode of ventilation and its settings. When the ventilator setting does not synchronize with the patient's respiratory pattern, the patient can easily have worsening breathing effort, patient-ventilator asynchrony, which can lead to prolonged ventilator support or lung injury. The information provided by the flow curves during mechanical ventilation, such as respiratory mechanics, the patient's effort, and patient-ventilator interactions, are very helpful when adjusting the ventilator setting. If clinicians can monitor and assess the flow curves information appropriately, it can be a useful diagnostic and therapeutic tool at the bedside. There may be association between inspiratory effort and flow, and this may further guide us, especially in the weaning process and when patients are not synchronizing with the ventilator. In this review, we try to gather information about "flow" that is scattered around in the literature and textbooks in one place. We will summarize the different flow waveforms utilized in commonly used ventilator modes with their advantages and disadvantages, information gained by the flow curves (i.e., flow-time, flow-volume, and flow-pressure), how to detect and manage asynchronies, and some ideas for future uses. Flow waveforms shapes and patterns are very beneficial for the management of patients undergoing mechanical ventilatory support. Attention to those waveforms can potentially improve patient outcomes. Clinicians should be familiar with this information and how to act upon them.

Transpulmonary driving pressure during mechanical ventilation–validation of a non‐invasive measurement method

“…In paper III we found that by applying respiratory resistance the time constant increased but so did the intrinsic PEEP. This is in coherence with previous studies that have shown that increased resistance in healthy lungs increases time constant, induces hyperinflation [149][150][151], increases carbon dioxide and decreases cardiac output [149,152]. Increasing PEEP irrespective of resistance increases the time constant too.…”

Static and Dynamic Measurements of Compliance and Driving Pressure: A Pilot Study

“…Since deflation may not occur uniexponentially (Hamahata et al, 2020), there are potentially multiple time constants throughout expiration. For the purposes of this study, two time constants were measured, and their mean was used to obtain an average for the compliance equation.…”

Mechanical ventilation for the non-critical care trained practitioner. Part 1

“…Reproduced by permission from Canadian Journal of Respiratory Therapy. 4 Whether the patient is actively breathing (active) or not (passive) the resultant airway pressure, flow wave forms and tidal volume might be different (Figure2)…”

“…Reproduced by permission from Canadian Journal of Respiratory Therapy. 4 Compliance/Resistance/Time-constant/Auto-PEEP Knowledge of the respiratory mechanics play a crucial role in diagnosing respiratory failure, in trending progress or regress of disease during treatment and in the weaning process.…”