Vertical Displacement Index and Early Treatment-Related Physiological Improvement in Acute Respiratory Failure: An Exploratory Ultrasound-Based Study

Objective: Rapid assessment of early treatment-related physiological improvement in emergency department (ED) patients with respiratory failure (RF) remains challenging. Blood gas analysis is informative but invasive and not ideal for repeated use. The vertical displacement index (VDI), an ultrasound-derived parameter based on pleural motion, may provide dynamic bedside information on early physiological change. This study evaluated whether changes in VDI are associated with early physiological improvement in ED patients with RF. Methods: This prospective observational study was conducted in the EDs of two tertiary care hospitals. Adult patients presenting with dyspnea and clinical evidence of RF were included. VDI was measured by lung ultrasound at baseline and 30 min after initial treatment. The primary endpoint was the change in VDI 30 min after the initial treatment, calculated as the difference between pre-treatment and post-treatment VDI. The expected direction was a post-treatment decrease in VDI, with greater VDI reduction expected to be associated with greater early physiological improvement. Secondary analyses included comparisons of VDI changes across oxygen saturation and diagnostic groups, as well as correlations between ΔVDI and physiological changes. Patients were grouped by admission oxygen saturation (<80%, 80–90%, and ≥90%). Results: Seventy-nine patients were included. Pre-treatment VDI differed significantly between oxygen saturation groups, with the highest values in the most hypoxemic patients (p = 0.028). VDI decreased significantly after treatment in all groups (p < 0.001 for all), with the greatest reduction in the <80% group. By diagnosis, VDI decreased significantly in pulmonary edema, COPD/asthma, and pneumonia, but not in pulmonary embolism (p = 0.138). VDI reduction correlated positively with improvements in oxygen saturation (r = 0.27, p = 0.016) and pH (r = 0.24, p = 0.037), but not with CO2. Conclusions: VDI may be explored as a practical ultrasound-derived bedside parameter associated with early physiological improvement in ED patients with RF.