The RSBI divides respiratory rate by tidal volume to gauge whether a patient is breathing in a sustainable pattern — a key predictor of whether they can come off the ventilator.
Favorable — weaning likely to succeed.
Borderline — weigh with the rest of the picture.
Above threshold — caution.
Weaning likely to fail.
Given: rate 20/min, tidal volume 400 mL.
Fast, shallow breathing pushes the index up and predicts weaning failure.
A value below 105 breaths/min/L predicts successful extubation; above 105 predicts a higher chance of failure. It's measured during a brief spontaneous breathing trial.
Small, fast breaths waste a larger fraction of each breath on dead space and signal that the respiratory muscles can't sustain adequate tidal volumes — a sign of fatigue or high load.
No. It's one piece alongside oxygenation, secretions, mental status, cough strength, and the overall clinical picture. A favorable RSBI supports but doesn't guarantee a successful wean.
During a spontaneous breathing trial with minimal or no support, the respiratory rate and average tidal volume are recorded, then rate is divided by tidal volume in liters.