Diaphragmatic Rapid Shallow Breathing Index Versus Diaphragmatic Thickness Fraction for Predicting Weaning Success in Mechanically Ventilated Patients.

Introduction Timely liberation from mechanical ventilation is a central goal of critical care. This study aimed to compare two point-of-care ultrasound indices, the diaphragmatic rapid shallow breathing index (D-RSBI) and the diaphragmatic thickness fraction (DTF), in predicting successful weaning among mechanically ventilated adults. Methods In this prospective, single-center diagnostic-accuracy study, 44 adults who were mechanically ventilated for more than 48 hours but fewer than seven days and who met the readiness criteria for a spontaneous breathing trial (SBT) underwent diaphragm and lung ultrasound before the trial. Weaning outcomes were categorized using the Weaning according to a New Definition (WIND) framework; successful weaning (simple or difficult categories, n = 36) was the reference standard, whereas prolonged weaning (n = 8) was considered the adverse outcome. Diagnostic performance was assessed at operating thresholds and by receiver operating characteristic (ROC) analysis, and the two indices were compared using the DeLong test (SPSS Statistics v23 (IBM Corp., Armonk, NY); MedCalc (Ostend, Belgium)). Results At a threshold of 1.2 breaths/min/mm, the D-RSBI showed strong diagnostic performance for successful weaning, with a sensitivity of 94.44% and specificity of 100% (area under the curve (AUC): 0.99, 95% confidence interval (CI): 0.97-1.00). The DTF discriminated poorly (sensitivity: 61.11%, specificity: 62.50%; AUC: 0.65, 95% CI: 0.42-0.88). The D-RSBI AUC was significantly higher than that of the DTF (DeLong p = 0.004). Notably, all eight patients with prolonged/failed weaning were also the eight most severely ill patients according to the Acute Physiology and Chronic Health Evaluation II score (APACHE II score, 13-21 vs. ≤ 10 in every patient who succeeded), and the direction of association for both indices was opposite to that reported in previous literature. Conclusions In this cohort, a D-RSBI ≥ 1.2 was strongly associated with successful weaning and outperformed the DTF. However, weaning outcome was completely determined by illness severity in this cohort, and the direction of the associations for both indices was inverted relative to prior studies. Therefore, these findings must be interpreted with caution and require validation in larger, multicenter cohorts.