With so many simultaneous issues transpiring in our critically ill patients, it is naive to think that one lab marker or one calculation would tell an absolute story. This has led to the erroneous mindset that every time the lactate is elevated, the patient has sepsis when we know that is not true. Another such parameter is the rapid shallow breathing index, aka RSBI (think frisbee but omit the F), for predicting successful extubation. Will the patient fly after extubation? Well, if their RSBI is less than 100, then likely yes was the thought process held by some. We’ve known, though, that there’s certainly more to it than that.

How to Calculate RSBI

RSBI = Respiratory Rate/Tidal Volume. The tidal volume is in liters.

Different studies have had different criteria. Generally speaking, over triple digits meant that they were going to fail extubation.

One can obtain these numbers by looking at the screen on the ventilator. I’d provide screenshots of this but there are so many different ventilators out there that I cannot obtain access to all of them. The other component is that the patient needs to be on a weaning modality such as pressure support. We should we conducting spontaneous awakening trials daily on appropriate patients.

What does the data say?

Trivedi et al. published a paper in CHEST that is unfortunately not free for you to download on the matter. They reviewed studies from 1991 all the way up to 2019. Fantastic work, team. 48 studies in all. Despite all these studies and differing patient populations, they were unable to tease out anything meaningful to determine if RSBI predicts successful extubation.

The RSBI showed moderate sensitivity and poor specificity as a stand-alone test. This means that one could continue to use it, but we need to take other parameters into account. Even if they brought down the number for <80 the results were still not impressive.

What do I do in my practice?

I cannot recall having used RSBI since residency. One of the things I trust more than a number is my clinical judgement. As the paper from Ouellette cited below emphasizes, there are a constellation of parameters that need to be considered. These include hemodynamic stability, resolution or a resolving process of what got them on the vent in the first place and an exit strategy to name a few.

The exit strategy is extremely important if you’re going to attempt a dicey extubation. Is the patient going to need supplemental O2? Will they get by with good ol’ nasal cannula? Will they need a venturi mask? Or will be need to step up our game and provide them with with high-flow nasal oxygen as mentioned in some guidelines or non-invasive ventilation?

This just might be one of those things in critical care where we will not be able to assign an index to due to all the underlying variables. RSBI will be a tool in the toolbelt, but not the multitool itself.

Hat tip to Dr. Parth Shah who caught a mistake I made in this post. Thanks!

Citations for RSBI

Trivedi V, Chaudhuri D, Jinah R, Piticaru J, Agarwal A, Liu K, McArthur E, Sklar MC, Friedrich JO, Rochwerg B, Burns KEA. The Usefulness of the Rapid Shallow Breathing Index in Predicting Successful Extubation: A Systematic Review and Meta-analysis. Chest. 2022 Jan;161(1):97-111. doi: 10.1016/j.chest.2021.06.030. Epub 2021 Jun 26. PMID: 34181953.
Link to Article (NOT FREE)

Ouellette DR. The Decision to Liberate From the Ventilator: More Than Just a Number. Chest. 2022 Jan;161(1):6-7. doi: 10.1016/j.chest.2021.07.016. PMID: 35000708.
Link to Article
Link to FULL FREE PDF

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