Ventilator Weaning Calculator

The Rapid Shallow Breathing Index is defined as breaths per minute divided by tidal volume in liters specifically so the result lands in the same numeric range (well under 105 for a favorable breathing pattern) that Yang and Tobin's original 1991 study established as predictive of weaning success. Using milliliters instead would shrink the ratio by a factor of a thousand and make the published 105 breaths/min/L cutoff meaningless, so this calculator always converts the entered tidal volume to liters before dividing.

No -- RSBI below 105 is the best-studied single predictor of weaning success, but published weaning protocols pair it with respiratory muscle strength (NIF), minute ventilation, oxygenation (P/F ratio), and PEEP requirement precisely because relying on one number risks missing a patient who breathes shallowly enough to pass RSBI but cannot sustain adequate gas exchange or has inadequate airway-protective reflexes, which this calculator does not assess at all.

Minute ventilation is respiratory rate multiplied by tidal volume, so it captures total air movement per minute rather than either component in isolation -- a patient can have a normal-looking respiratory rate but still show elevated minute ventilation if each breath is unusually large, or vice versa. A minute ventilation under roughly 10-12 L/min is generally reassuring because it suggests the patient is not compensating for a high metabolic or dead-space burden with excessive total ventilation.

The P/F ratio divides arterial oxygen pressure by the fraction of inspired oxygen, so a low value means the lungs need a disproportionate amount of supplemental oxygen to maintain adequate arterial oxygenation -- a sign of significant gas-exchange impairment. A ratio below roughly 150-200 is generally considered unfavorable for extubation because removing ventilator support typically removes some of the recruitment pressure keeping alveoli open, which can worsen oxygenation further once the patient is off the machine.