Jul 8, 20217 min read

Weapon of Choice During Your RSI: Pre-Oxygenation

When I think of Deadpool, I think of a medic… Rad as hell, gets the job done and usually has good intentions. Buuuut, Deadpool is also very chaotic, oftentimes choosing the cool weapons, or the more flashy approach, over the practical ones. The weapon/approach he selects varies depending on the circumstances. But the “wow” or “cool” factor that gets the most attention… seems to be his general choice. This is often the same thought I have about medics (but applies to many other pre-hospital and in-hospital providers as well) — Especially during procedures such as RSI.

You don’t often hear about the boring side of interventions or procedures such as RSI. In fact, I would bet that during your shift change you’ve heard ‘war story’ banter about procedures such as RSI, with questions along the lines of, “What size tube did you use” or “What induction agent did you choose?” Even though those are good things to discuss and things we’d all like to know, it’s really just a small spec in the grand scheme of the procedure. And honestly, it oftentimes doesn’t have as large of an impact on morbidity and mortality as other portions of the overall procedure.

That’s where pre-oxygenation comes in. It seems to be the neglected portion of the overall procedure (but not the only one). With all of the FOAMed material out there on this, I’m really clueless as to why this is a subject that needs attention. But during some of my ‘war story’ banter, I hear many - often times very intelligent providers - pushing their drugs for induction and paralysis when the patient has saturations in the 80's… WHAT?! But they followed it up, bragging about all the other rad things they did or saw. C’mon, man!

I know what some of you may be thinking: “But, Jared, you weren’t there.” Sure, you’re right… I wasn’t. But I can also hear a story that makes me grit my teeth in nervousness. The problem I have with this is the fact that there are plenty of accredited courses and education opportunities out there that try to prevent such atrocities from occurring. The other problem I have is that plenty of people are having success without taking all of the proper precautions to assure their chances of success are the greatest, let alone giving the patient the best shot at surviving such an invasive procedure. Many providers don’t see what’s wrong with what they are doing because the patient faired well after the encounter, regardless of their poor choices.

When you think of choosing a weapon for RSI, we often think of the equipment seen in the above picture. Which, ideally, it would be nice to have all of it, although it’s not always the case. Now, I was gonna choose the nasal cannula (as my weapon of choice) with the direction I was going with the blog, but as I started writing, I opted for an approach instead. And if you haven’t guessed it, it’s the utilization of pre-oxygenation prior to induction and paralysis. Preoxygenation is my "Weapon of Choice."

*** “Placement” is highlighted, because it’s the most discussed portion of RSI, but plays such a small role in the grand scheme of the entire procedure ***

Above, you’ll see an image of the ‘7 P’s of RSI.” Which, is only one of many mnemonics that are over-utilized and easily forgotten in our industry. Some others may have heard about the ‘8 P’s of RSI.’ It’s the same 💩. Even though I’m not a huge fan of mnemonics, I DO believe that this is one that IS helpful when doing initial education on RSI (emphasis on initial education). It’s kind of a step-by-step guide to learning the process.

If you haven’t noticed, pre-oxygenation is one of the ‘7 P’s of RSI.’ Meaning that it’s obviously 1/7th of the entire procedure (DUH!). Even though it’s only 14.285714% of the entire procedure, I find it to be one of the most important. Why do I think it’s really important? Because of this:

^^^ This is referred to as the oxyhemoglobin desaturation curve. The chart shows the time to desaturation in patients who have been adequately pre-oxygenated prior to induction. Look at it closely, it’s actually pretty darn interesting.

Why is it important?

Well, it’s a chart that gives us an approximation of the time until desaturation during a procedure such as rapid sequence induction. It illustrates that if a patient is fully pre-oxygenated prior to induction, depending on their status and degree of illness, they can maintain an oxygen saturation above the critical desaturation rate of 88 to 90% for upwards of 8 minutes.

You may also ask, why is that important?

Well, the lower the oxygen saturation is during a procedure such as rapid sequence induction, the higher the risk for dysrhythmia, hemodynamic instability, hypoxic brain injury, or just plain old death.

We are doing our patient’s a disservice by not appropriately pre-oxygenating them prior to induction and paralysis, and in my opinion, there is almost no reason ever to not make an attempt at pre-oxygenation prior to induction -- and I'm sure many of you RSI nerds out there would agree. By appropriately pre-oxygenating our patients, we are making attempts to give them the best neurological outcome possible -- mitigating the effects of hypoxia during the procedure.

Now, I completely understand that we sometimes have no way of accurately estimating how long the patient will maintain an oxygen saturation above the critical desaturation rate. But what we do know is that we can prolong the safe apnea phase by making every effort we can to pre-oxygenate our patient.

I think Scott Weingart and Rich Levitan say it best in their paper, Pre-oxygenation and Prevention of Desaturation During Emergency Airway Management. They say, “It is impossible to predict the exact duration of safe apnea in a patient. Patients with high saturation levels on room air or after oxygen administration are at lower risk and may maintain adequate oxygen saturations as long as 8 minutes.”

I hope at this point in the blog, you don’t feel like I’m blowing smoke up your bum. So I think I should answer a couple of common questions I get regarding pre-oxygenation.

"What is Pre-Oxygenation?"

Pre-oxygenation, per the Manual of Emergency Airway Management, is, “The establishment of an oxygen reservoir within the lungs, blood, and body tissue to permit several minutes of apnea to occur without arterial oxygen desaturation.” With the administration of 100% oxygen for several minutes, we replace the dominant gas, nitrogen, within the lungs with oxygen. This then allows that prolonged "safe apnea time" I mentioned earlier.

This always leads to the question:

"What is safe apnea time?"

Safe apnea time is the duration of time until critical desaturation, which occurs or starts following the cessation of breathing. Once the oxygen saturation has decreased to approximately 88 - 90%, or the critical desaturation range, a precipitous drop occurs and the harmful effects of hypoxia can manifest very quickly. So the better we pre-oxygenate our patients, the longer the possible safe apnea time is.

I would be remiss to not include that the patient population and condition do greatly affect the safe apnea time. The pediatric, obese, late-term pregnancy population will desaturate faster than a healthy adult would. And, any patient who is critically ill or has a likelihood of shock is at risk for immediate desaturation as well; sometimes within 30 seconds.

While I can’t tell you how fast they will desaturate, I will stick to the idea that if you appropriately pre-oxygenate a patient, their safe apnea time will be longer than that of no pre-oxygenation at all.

*** Following appropriate pre-oxygenation, the patient will maintain oxygen saturation for an extended amount of time, compared to no pre-oxygenation at all. But once the critical desaturation range is met, a precipitous drop will occur… and fast ***

"How do I pre-oxygenate my patient?"

Well, this one honestly might be the most simple… Or, at least I am gonna make it as simple as I can.

You deliver 100% oxygen for 3 to 5 minutes to your patient by whatever method is appropriate for the patient’s condition. The goal is to deliver the highest FiO2 possible in order to establish a reservoir of oxygen within the lungs and replacing the mixture of alveolar gases with that sweet, sweet O2. This creates an “oxygen reserve” which will provide a source of oxygen the pulmonary circulation can still utilize during the apneic period prior to insertion of an airway device.

So, I said to "deliver 100% oxygen for 3 to 5 minutes by whatever method is appropriate for the patient’s condition." I bet you want me to give an example? Absolutely, but we’re gonna save that for another blog. Mainly cause this is already getting long and I don’t want to lose your attention (If I haven’t already).

I know there is so much more to RSI than pre-oxygenation. But pre-oxygenation is one of those topics that I am not only passionate about, but I feel has saved my @$$ on multiple occasions. I'm not gonna knock the other "P's," but I will share that in my opinion, pre-oxygenation is pretty darned important and would be my "Weapon of Choice" if you made me choose which part I thought was most crucial.

I know we all have our convictions when it comes to RSI. Which weapon or approach would you choose? Do you agree? Disagree?

Here is Scott Weigart and Rich Levitan's paper from the Annals of Emergency Medicine:

https://www.annemergmed.com/article/S0196-0644%2811%2901667-2/fulltext

Keep an eye out for more regarding this topic. Pre-intubation optimization would have been my next "Weapon/Approach of Choice" 😉