The Rapid Shallow Breathing Index (RSBI) (respiratory rate f / tidal volume VT) is a crucial indicator for predicting whether a patient can successfully wean off mechanical ventilation.

This study aims to explore the clinical value of measuring RSBI using different methods in predicting successful extubation. Study Methods: A prospective study was conducted in the medical and surgical intensive care units of a teaching hospital. Data were collected from patients who required intubation and mechanical ventilation due to respiratory failure from August 2024 to July 2026. The RSBI measured under different ventilator settings was compared with the traditional standard hand-held Wright spirometer measurement. The ventilator measurement methods were divided into three categories: PSV 5 cmH2O with PEEP 5 cmH2O, CPAP 5 cmH2O, and CPAP 0 cmH2O. The study analyzed the differences in RSBI measurements obtained by these methods and their ability to predict successful extubation, as well as other related factors, including the influence of different ventilator models, ventilation modes, and parameter settings on RSBI values. RSBI can vary across different patient populations and measurement methods. This study aims to validate the RSBI displayed by ventilators against the traditional standard measurement, providing a reliable predictive capability for successful extubation.

Furthermore, it seeks to facilitate clinical application and assist healthcare providers in determining the appropriate timing for extubation, reducing unnecessary prolonged use or premature removal of mechanical ventilation, and thereby lowering the incidence of complications and healthcare costs.

In the Intensive Care Unit (ICU), approximately 25% of patients undergoing mechanical ventilation may experience difficulties during weaning from the ventilator. This can lead to delayed extubation, prolonged mechanical ventilation, increased length of stay in the hospital or ICU, and higher healthcare costs. On the other hand, premature extubation can result in secondary complications, increasing morbidity and mortality rates in the ICU. About 15% of patients who stop mechanical ventilation require reintubation within 48 hours. Therefore, it is crucial for intensivists to determine the appropriate timing for weaning from mechanical ventilation and successful extubation.

A study by Yang and Tobin in 1991 discovered that the ratio of respiratory rate to tidal volume (f/VT), known as the Rapid Shallow Breathing Index (RSBI), can serve as a predictor for successful weaning from mechanical ventilation. An RSBI value of <105 is considered indicative of a higher likelihood of successful extubation, while an RSBI value of >105 suggests a greater chance of weaning failure. The Wright spirometer is commonly used in clinical practice to measure RSBI. In practice, the spirometer is connected to the artificial airway, and the ventilator is disconnected for a 60-second respiratory measurement, without the need for additional complex equipment.

However, due to advancements in medical technology, ventilator parameters can also be used to calculate RSBI during Spontaneous Breathing Trials (SBT). Utilizing the ventilator to assess RSBI avoids interruptions in ventilation and reduces measurement risks. Research has shown that ventilator-calculated RSBI is convenient for clinical use and is feasible in predicting weaning outcomes. Nevertheless, variations in ventilator models, such as differences in base flow, type of ventilator, pressure compensation, Positive End-Expiratory Pressure (PEEP), and bias flow, may affect the accuracy of RSBI measurements obtained from the ventilator.

This study aims to further explore whether different measurement methods affect the accuracy of RSBI. However, weaning profiles should be evaluated comprehensively using additional parameters beyond RSBI, especially for patients requiring airway protection, increased secretions, or poor cough strength. Factors such as cough strength and the amount of secretions should be considered. A study on Chronic Obstructive Pulmonary Disease (COPD) patients found that early RSBI measurements did not accurately predict success in SBT; thus, this study will also analyze different disease diagnoses to provide reference for clinical assessment.

End-expiratory lung volume (EELV) is the lung volume at the end of expiration, representing the balance point between chest wall elastic recoil and lung collapse tendency, and is a major factor in determining lung oxygenation capacity. Changes in EELV are clinically significant, with studies indicating that a decrease in dorsal EELV slope is a strong predictor of lung collapse. Additionally, changes in EELV during SBT may be related to the patient's ability to successfully wean from mechanical ventilation. Electrical Impedance Tomography (EIT) measures changes in lung impedance based on variations in tissue and air distribution, providing cross-sectional images. EELV can be estimated from End-expiratory Lung Impedance (EELI), which will be included as an analysis parameter alongside different RSBI measurement methods.

Hypothesis: There is no significant difference between RSBI values obtained from ventilator measurements and those obtained using traditional handheld spirometry in predicting successful extubation.

Clinical Benefits: Traditional handheld spirometry requires temporarily disconnecting the ventilator, exposing staff to aerosolized droplets and potentially causing hypoxemia in patients dependent on oxygen support, which may lead to abnormal physiological parameters and increased patient risk. During the COVID-19 pandemic, traditional spirometry was not suitable due to airborne infection control requirements, and concerns about cross-infection between patients with reusable Wright spirometers were significant. Using the ventilator to measure RSBI is a feasible alternative. Currently, SBT is commonly used to evaluate extubation success in critically ill patients. Using the ventilator for RSBI measurements during SBT facilitates data acquisition and reduces environmental contamination between the ventilator and the patient.

There is still debate over the standard value for RSBI measurements obtained from ventilators compared to traditional methods. Some studies indicate similar results between traditional spirometry and ventilator-measured RSBI, while others show significantly higher RSBI values with traditional spirometry. This study will compare three different ventilator measurement methods with traditional standard measurements to explore differences in predicting extubation success. Additionally, changes in EELI will be compared across the four RSBI measurement methods.

Inclusion Criteria:

• Age 18 years or older.
• Admission to the Intensive Care Unit (ICU).
• Endotracheal intubation with mechanical ventilation for more than 24 hours.
• P/F ratio > 150; FiO2 ≤ 40% and Positive End-Expiratory Pressure (PEEP) ≤ 8 cmH2O.
• Hemodynamically stable, without the need for vasoactive drugs or requiring only low doses.

Exclusion Criteria:

• Significant cardiac ischemia or arrhythmia.
• Patients with a tracheostomy.
• Patients with an endotracheal tube with an internal diameter smaller than 7.0 mm.
• Patients who have undergone repeated intubations within the past month.

ICU patients for whom the attending physician anticipates initiation of a Spontaneous Breathing Trial (SBT) and plans for extubation.