The term preoxygenation means different things to different people. In most of the anesthesia literature when that term appears, what is actually meant is denitrogenation. This meaning has been muddled to encompass all of preintubation oxygenation prep. This meaning actually works for most elective anesthetic cases, as if you take a relatively well patient and denitrogenate them with an FiO2 1.0 source, you will also accomplish the other steps of preintubation preparation without thought. However in the critically ill patient in the field, the ED, or the ICU (or the OR when the patient is not well), oxygen is only part of the picture to accomplish an oxygen reservoir.
I was recently part of a conversation on a mailing list with a group working on an ETO2 project. During a discussion of the above ideas, Nick Caputo (of amazing-airway-studies fame) said the better term may be Oxygenation Optimization. That was pretty good, but it did not form the properly scatological acronym that we need here on EMCrit. Henceforth I will refer to…
Preintubation Oxygenation Optimization
POO consists of 3 separate acts, all of which are essential to prevent rapid desaturation during airway management:
1. Denitrogenation (known in the literature as preoxygenation): Alveolar washout of nitrogen +/- blood/cellular washout) with the proxy marker being ETO2. If you don't have ETO2 (you are going to be hearing a lot more about this from Dr. Caputo and a host of other excellent researchers), then you are forced to use time-based surrogates, i.e. 3 minutes of cont. breathing on high FiO2 source.
2. Physio Shunt Redution/Elimination: full alveolar recruitment to the maximal extent possible. If you have not achieved 100% sat on FiO2 1.0 (patient should already be on such a source for step 1) then it is a negative marker of success (Achieving 100% sat unfortunately is not a positive marker). A better marker is PaO2 (actually the Aa gradient but this is easily intuited when on FiO2 1.0). The ideal would be to calculate a shunt fraction (ain't gonna happen). If you are not achieving this step with FiO2 augmentation, you need to increase the mean airway pressure with PEEP/CPAP.
3. Optimization of SvO2: Venous admixture with low SvO2 blood is the cause of rapid desat in crit care intubations (shunt combined with low SvO2=dead in seconds). See this EMCrit Podcast for more on this. I guess the surrogates here would be a quick echo and the quality of your SpO2 waveform , which probably should be added to my teaching of how not to kill a patient when intubating. If the CO looks like crap, augment that before you intubate.
It is very easy to achieve 1 of these without the others. And when we roll all of them into one term=failed discussions/failed planning/failed intubations.
So POO will keep you out of the poo. You might ask why not just reclaim the term preoxygenation and make it mean all of the above, but that would make all of the existing literature even more difficult to parse.
For More on Preox, see the EMCrit Preox Page
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- EMCrit Wee – Stop Kneejerk Intubation with the EMCrit Crew - March 30, 2020