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.
Positive — extubation likely to succeed.
Borderline — weigh the full clinical picture.
Negative — above threshold, higher failure risk.
Negative — weaning likely to fail.
A value above 105 should not prevent extubation if the overall clinical picture is favorable. Several factors can falsely elevate the RSBI:
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 is a positive result — it supports extubation when other criteria are met. Above 105 is negative, predicting a higher failure risk. The original Yang & Tobin threshold was 105.
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 — and it is not meant to answer whether a patient is ready for extubation on its own. It's one piece alongside oxygenation, secretion burden, mental status, cough strength, and the overall clinical picture.
During a spontaneous breathing trial with minimal or no ventilator support, the respiratory rate and average tidal volume are recorded over one to two minutes, then rate is divided by tidal volume in liters.
Female sex (naturally smaller tidal volumes), a smaller endotracheal tube (increased resistance lowers measured Vt), and active suctioning during measurement (transiently raises respiratory rate) can all push the index above 105 even when the patient is ready to wean.