Calculator for RSBI \(= \frac{f}{V_T(\mathrm{L})}\) and Minute Ventilation \(\dot V_E = f \cdot V_T(\mathrm{L})\), with animation and mathematical notation equations.
The Rapid Shallow Breathing Index (RSBI), the ratio of respiratory rate (f) to tidal volume (VT) in liters, was first described by Yang and Tobin (1991) as a bedside predictor of weaning success. The calculation, expressed as f/VT, quantifies the efficiency of a patient’s spontaneous breathing effort. An RSBI ≤ 105 breaths·min⁻¹·L⁻¹ obtained during a spontaneous breathing trial (SBT) has been correlated with a higher likelihood of successful extubation and ventilator liberation.
Clinically, the RSBI serves as a rapid, noninvasive indicator of ventilatory mechanics and patient endurance. A lower RSBI suggests that the patient generates adequate tidal volumes without excessive respiratory frequency—reflecting effective neuromuscular drive, respiratory muscle strength, and ventilatory reserve. Conversely, a high RSBI reflects rapid, shallow breathing and often anticipates weaning failure.
Despite widespread use, RSBI has moderate sensitivity and poor specificity as a stand-alone test across heterogeneous ICU populations; threshold performance varies by disease state and by how the SBT is conducted (e.g., pressure support vs. T-piece). Importantly, RSBI is a ratio: a proportionally low f and low VT can produce a “favorable” RSBI while overall ventilation and gas exchange remain inadequate. RSBI also does not directly capture inspiratory effort, diaphragm performance, secretion burden, mental status, airway protection, or hemodynamic stability. Accordingly, contemporary guidance recommends not using RSBI in isolation but integrating it with a broader liberation assessment.