Modified Rapid Shallow Breathing Index Adjusted With Anthropometric Parameters Increases Predictive Power for Extubation Failure Compared With the Unmodified Index in Postcardiac Surgery Patients

Objective The aim of this study was to determine the best predictors of successful extubation after cardiac surgery, by modifying the rapid shallow breathing index (RSBI) based on patients’ anthropometric parameters. Design Single-center prospective observational study. Setting Two general intensive care units at a single research institute. Participants Patients who had undergone uncomplicated cardiac surgery. Interventions None. Measurements and Main Results The following parameters were investigated in conjunction with modification of the RSBI: Actual body weight (ABW), predicted body weight, ideal body weight, body mass index (BMI), and body surface area. Using the first set of patient data, RSBI threshold and modified RSBI for extubation failure were determined (threshold value; RSBI: 77 breaths/min (bpm)/L, RSBI adjusted with ABW: 5.0 bpm×kg/mL, RSBI adjusted with BMI: 2.0 bpm×BMI/mL). These threshold values for RSBI and RSBI adjusted with ABW or BMI were validated using the second set of patient data. Sensitivity values for RSBI, RSBI modified with ABW, and RSBI modified with BMI were 91%, 100%, and 100%, respectively. The corresponding specificity values were 89%, 92%, and 93%, and the corresponding receiver operator characteristic values were 0.951, 0.977, and 0.980, respectively. Conclusions Modified RSBI adjusted based on ABW or BMI has greater predictive power than conventional RSBI.