Assessment of the Rapid Shallow Breathing Index, Integrative Weaning Index, and Dead Space to Tidal Volume Ratio by Respiratory Failure Type in Successfully Weaned Emergency Department Patients

<i>Background/Objectives</i>: Mechanical ventilation is essential in the management of acute respiratory failure (RF); however, prolonged use increases the risk of complications. Accurate predictors are therefore needed to guide timely weaning. The Rapid Shallow Breathing Index (RSBI), the dead space to tidal volume ratio (VD/VT), and the Integrative Weaning Index (IWI) are among the key indices used to assess weaning readiness. This study aimed to examine whether these indices differ between patients with Type 1 (hypoxemic) and Type 2 (hypercapnic) respiratory failure who were successfully extubated in the emergency department, in order to explore their physiologic variability across respiratory failure phenotypes. <i>Methods</i>: This cross-sectional study included 35 adult patients (23 with Type 1 RF, 12 with Type 2 RF) who were successfully weaned from mechanical ventilation in the Emergency Department of a tertiary care hospital between 2022 and 2024. RSBI, VD/VT, IWI, and arterial blood gas parameters were recorded. Descriptive and comparative statistical analyses were performed, with significance set at <i>p</i> < 0.05. <i>Results</i>: There were no significant differences in age, gender, or comorbidities between the groups. Type 2 RF patients had higher FiO₂ requirements (37.5% vs. 30.0%; <i>p</i> = 0.03) and PaCO₂ levels (49.1 ± 9.65 mmHg vs. 40.3 ± 4.49 mmHg; <i>p</i> < 0.001). The PaO₂/FiO₂ ratio was lower in the Type 2 group (169 ± 49.6) compared to the Type 1 group (244 ± 95.6; <i>p</i> = 0.017). VD/VT ratios were significantly higher in Type 2 RF patients (0.37 ± 0.04 vs. 0.29 ± 0.13; <i>p</i> = 0.046). RSBI values were identical between groups (40.0 in both; <i>p</i> = 1.00), and IWI values showed no significant difference (70.8 ± 30.7 vs. 79.3 ± 32.5; <i>p</i> = 0.45). <i>Conclusions</i>: Although RSBI and IWI values were similar across respiratory failure types, patients with Type 2 RF demonstrated higher VD/VT ratios and lower PaO₂/FiO₂, indicating reduced gas exchange and alveolar ventilation efficiency. These findings suggest that VD/VT may be a more useful parameter for assessing weaning readiness in hypercapnic patients.