A Study on the Diagnostic Accuracy of Tidal Volume-Diaphragmatic Contraction Velocity: A Novel Index for Weaning Outcome Prediction

Objectives: Weaning failure from mechanical ventilation (MV) is primarily caused by increased respiratory load and decreased respiratory neuromuscular competency, leading to a rapid shallow breathing pattern. We hypothesized that the product of diaphragmatic contraction velocity (a sonographic estimate of respiratory load) and tidal volume (an estimate of breathing pattern), termed the volume-velocity index (VVI), may predict weaning outcomes. Design: The diagnostic accuracy of VVI (mL*cm/s) in predicting weaning outcomes was prospectively assessed, along with its relationship to indices of breathing effort, including esophageal pressure swings (ΔPes), the pressure-time product of esophageal pressure (PTPes), and maximal inspiratory pressure (MIP). A power analysis, informed by the results of an inception cohort, determined the required sample size for the validation cohort. Patients were enrolled through consecutive sampling. Weaning failure was defined as failure of the spontaneous breathing trial (SBT) or the need for MV within 48 hours. Setting: The study was conducted in a tertiary academic ICU. Patients: VVI was evaluated in critical care patients undergoing a SBT for the first time. Interventions: None. Measurements and Main Results: In the inception cohort ( n = 30), VVI was significantly higher in successful weaning compared to failures (764.76 [±432.61] vs. 278 [±183.66], p < 0.001). It correlated with ΔPes ( r = 0.74, R 2 = 0.55), PTPes ( r = 0.76, R 2 = 0.58), and MIP ( r = 0.75, R 2 = 0.55) all p values less than 0.001. In the validation cohort ( n = 40), VVI was higher in successful weaning (840 [550, 1220] vs. 250 [225, 302.5], p < 0.001) and predicted weaning success with an area under the receiver operating characteristic of 0.92 (95% CI, 0.83–1). Conclusions: VVI effectively differentiates between weaning success and failure, shows a strong correlation with respiratory effort indices, and may enhance weaning protocols.