RSBI Calculator - Rapid Shallow Breathing Index

The rapid shallow breathing index is the ratio of respiratory frequency (f) to tidal volume (TV), measured in liters:

RSBI = f / TV

Respiratory frequency is a simple count of breaths per minute. To measure tidal volume, you should use a spirometer. Using this device, you will also find other parameters, like the patient's vital capacity, and other lung capacities, e.g., total lung capacity. Find out more in our specific tools: vital capacity calculator and how to calculate total lung capacity

Measuring RSBI requires the temporary stopping of the mechanical ventilation but leaving the endotracheal tube in.

1. This RSBI calculator is very easy to use. Take a look at the panel on your left.
2. First, input the patient's respiratory rate, which means the number of breaths per minute.
3. In the second field, put in the tidal volume, measured in milliliters. You may have noticed the RSBI formula uses TV (tidal volume) in liters, and here we ask you to give it in milliliters - but it's okay - the RSBI calculator will deal with it.
4. The third field is your result.
5. You'll also find a short comment below the result.

Patients with respiratory failure are sometimes in such a severe state they need to be put on mechanical ventilation for some time. The classical solution requires sedating the patient, and then connecting them to the ventilator through an endotracheal tube. Breathing disorders are always reflected in arterial blood gases measurements (not always in the arterial blood pH, though).

But, counter-intuitively, the goal of mechanical ventilation therapy is... to get rid of it as soon as possible. As soon as the patient can breathe properly on their own, they should be taken off the machine. To estimate the chances of a positive outcome, physicians use a few tests to assess the patient's state. One of them is RSBI.

RSBI - rapid shallow breathing index - is simple to use as it has only one cut-off point, 105. If the RSBI score is lower than 105 is a good prognosis that the future weaning from mechanical ventilation will be successful, and - logically - a result above 105 indicates a reduced chance to do that.

Where does this measure come from? Well, persons who are not able to breathe effectively on their own tend to breathe rapidly (in the medical language breathing with a frequency greater than 20 breaths/minute is called tachypnea) and shallowly. Thus, their RSBI score will be high. On the other hand, people without respiratory disorders take deeper, slower breaths - and so their RSBI will be low.