The Clinical Feasibility and Validity of Simple Measurement of Inspiratory Muscle Pressure Index (PMIvent) to Access Inspiratory Effort During Pressure Support Ventilation

The intensity of effort the respiratory system produces after receiving respiratory center drive is referred to as inspiratory effort. It is critical to maintain a relatively normal inspiratory effort during assist mechanical ventilation. During pressure support ventilation (PSV), the support level should be adjusted to match the patient's inspiratory effort.

The inspiratory muscle pressure index (PMI) is an indicator based on airway pressure (Paw), defined as the difference between plateau pressure (Pplat) and airway peak pressure (Ppeak). PMI can reflect the elastic work of the respiratory system at the end of inspiration and has a significant correlation with end-inspiratory muscle pressure (Pmus,ei) and esophageal pressure time product per breath (PTPes). Current studies have shown that PMI is an accurate indicator of inspiratory effort, and it has the outgoing advantages of being non-invasive and easy to obtain.

Previous studies on PMI were based on physiological research and experimental conditions, which require special pressure monitoring devices and software to collect and measure airway pressure. In this investigation, the standard measurement of PMI (PMIref) was the difference between Pplat at one cardiac cycle (0.5-1.2s) following end-inspiratory occlusion (EIO) and Ppeak at EIO. This measurement method can avoid the interference of cardiac artifacts on Paw to the greatest extent. If PMI is going to be used in clinical practice, it is necessary to find a simple measurement method of PMI to replace PMIref. Most ventilators have airway pressure monitoring and end-inspiratory holding functions, and PMI can be measured by freezing the ventilator screen (PMIvent). When obtaining PMIvent, the operator could only select a relatively stationary Pplat by visual inspection, and the cardiac artifacts could not be avoided.

Several additional issues need to be addressed when PMI is going to be used in clinical practice to monitor inspiratory effort in ventilated patients. Is PMI easy to obtain? Can PMIvent replace PMIref? What is the effect of different ventilators on PMIvent measurement? What is the relationship between PMIvent and inspiratory effort? Can PMIvent detect high/low effort? Therefore, the aims of this study were to explore the clinical acquisition rate of PMI, the agreement between PMIvent and PMIref, and the predicted value of PMIvent for inspiratory effort. The overall aim was to determine PMI's clinical feasibility and validity for accessing inspiratory effort during PSV.