Weapons Used for Pre-Oxygenation
In my previous blog, Weapon of Choice During Your RSI: Pre-Oxygenation, I discussed the importance of pre-oxygenation as it relates to the rapid sequence induction procedure and why it is my “Weapon (or approach) of Choice.” If you haven’t already taken a gander at it, I suggest reading it here before continuing on. The previous blog was a rundown of the basics of pre-oxygenation, answering the questions:
What is pre-oxygenation?
What is safe apnea time?
How do I pre-oxygenate my patient?
But I left that last question only partially answered — well, for the most part. And really, that’s because the full answer really is “administer 100% oxygen for 3 - 5 minutes by whatever method is appropriate.” If you do just that, you will have effectively pre-oxygenated your patient. The other reason I didn’t answer the question in its entirety? it would have made the blog incredibly looooong… and you’ll see why with the addition of this article and yet another one to follow 😬😬😬
You’re beating around the bush, Jared, just answer the question! HOW SPECIFICALLY DO I ADMINISTER 100% FOR 3 - 5 MINUTES BY WHATEVER METHOD IS APPROPRIATE?!
I’ll get to that, But first... a tidbit of what I think is necessary education or “PEARLS,” if you will, that will help with understanding the method to pre-oxygenating our patients — because the method does seem a tad out of the ordinary.
Traditional Supplemental Oxygen delivery devices are deceiving. I bet you’ve been led to believe that the non-rebreather mask (NRB/NRM) you have in the ambulance or the emergency room is capable of delivering nearly 100% oxygen. I was under that impression as well — paramedic school taught it to me and it says so in the books. And it’s true if you have an actual non-rebreather mask with two functioning one-way valves, a full reservoir bag, and a perfect mask seal… Oh, and a liter flow exceeding the patient’s current minute ventilation.
But I bet that if you pulled out that non-rebreather mask from your department's stock, it only has one, one-way valve and another opening on the other side of the mask that is open to the atmosphere. Getting a perfect seal on that deformed piece of plastic? Good luck! And I bet you set the oxygen to 10 - 15 LPM on the mask too… This all allows for the possible entrainment of room air through the device if the patient has a high minute volume while sucking wind prior to your RSI procedure. This means that your device is likely limited to, at best, 70% FiO2 delivery. Which, we want as close to 100% as possible when pre-oxygenating our patients for RSI.
This entrainment of room air can be mitigated by altering our standard flow rates. If we set our flow meters to “flush” rates (> 40 LPM) it is possible to approach an FiO2 of 100%. This high liter flow compensates for mask leaks. This is usually only possible if you have a Thorpe Tube available (pictured below).
For a more in-depth dive into this logic, read Sam Irelands blog: You Versus the Atmosphere (100% FiO2?)
You may be caring for patients in the pre-hospital environment and are working with devices that have limited liter flow, often times restricted to 15 LPM (or 25 LPM in some). This makes the previous PEARL difficult to accomplish. How are you supposed to apply “flush” rate oxygen to your patients?
That’s where the nasal cannula comes into play. Not only is it a commonly accepted adjunct to pre-oxygenation, but it can be utilized for apneic oxygenation as well. You simply apply the nasal cannula under the non-rebreather mask and run the nasal cannula at 15 LPM. This would effectively deliver approximately 30 LPM of oxygen during your pre-ox in conjunction with the non-rebreather (with BOTH set to 15 LPM, although if you can increase the NRB flow higher, do it — MAX FLOW, BABY!!)
The pitfalls to this are needing two oxygen cylinders capable of delivering the required flow and your overall supply of oxygen — running oxygen at these liter flows will deplete the already limited oxygen supply for pre-hospital providers.
And before you ask, it IS safe to run a standard cannula at 15 LPM, or faster. Check this article out on EMCrit: Preoxygenation & Apneic Oxygenation Using a Nasal Cannula. The primary drawback to the nasal cannula at such high flow is that it isn't heated or humidified, which can be uncomfortable for the patient.
DO NOT USE THE EtCO2 NASAL CANNULA FOR PRE-OXYGENATION!
EtCO2 nasal cannulas, or capno-lines as some call them, don't deliver oxygen through the nasal prongs as a standard cannula does. Oftentimes, in the EtCO2 variation, those prongs are used for aspiration of exhaled gases for your cardiac monitor to give you that qualitative and quantitative CO2 reading. It is your responsibility to know your department's equipment and understand how the device works.
The BVM is capable of delivering 100% FiO2 at 15 LPM with a robust mask seal maintained. This can be utilized for your apneic and spontaneously breathing patients. But keep in mind, if the seal is broken or inadequate, the patient may draw in room air around the mask during inspiration which could lower the FiO2 delivered substantially.
One should also be acutely aware that not all BVMs are the same. A bag-valve mask WITHOUT a one-way exhalation valve allows room air into the mix. A bag-valve mask WITH a one-way exhalation valve is capable of providing 100% oxygen, again only if a perfect mask seal is maintained.
"Flush" rate with a bag-valve mask has not been studied but is reasonable if a poor mask seal is suspected.
I will direct you to another one of Sam Ireland's blogs: The FiO2 Fallacy where Sam this time dives into the anatomy of a BVM. I highly suggest you read it!
Non-invasive positive pressure ventilation; or, CPAP/BiPAP for you in the back. Patients may be obese or have shunt physiology, such as pulmonary edema, pneumonia, or ARDS. These patients oftentimes can’t achieve optimal pre-oxygenation without the assistance of PEEP.
Increased airway pressure is needed to open the alveoli for maximal nitrogen washout, oxygen storage, and overall gas exchange. The implementation of CPAP or BiPAP may be indicated in patients who can not achieve or maintain oxygen saturation > 94% with “flush” rate oxygen alone.
Non-invasive positive pressure ventilation can also be applied by bag-valve mask with PEEP if manual ventilation is indicated.
Position your patient upright, if possible. Oxygen storing capacity within the lungs is the greatest when the patients are sitting up. Pre-oxygenation is significantly more effective when the patient is upright allowing better use of the patient’s functional residual capacity (FRC; the area the blood will draw oxygen from during the apneic phase).
Even if you are ventilating an apneic patient with a bag-valve mask, head elevation at 20 to 30 degrees is better than supine.
When we are pre-oxygenating our patients, we are also hoping that they become denitrogenated as well — that’s part of the 3-5 minutes we spend with the patient on “flush” rate oxygen flow.
As you sit currently, you are inhaling approximately 21% oxygen, 78% nitrogen, and a fraction of other gases like farts. If we replace the predominant gas, nitrogen, within our lungs with oxygen, we are prolonging the safe apnea time.
*** Sam's illustration used in his blog, You Versus the Atmosphere (100% FiO2?). It demonstrates that 100% FiO2 is necessary to effectively "denitrogenate" our lungs. ***
Ok, OK, OKAY!
I will now share with you, “How to specifically administer 100% oxygen to our patients.”
The Pre-Oxygenation Procedure:
If the patient is spontaneously breathing with adequate respiratory drive, ensure airway patency and place them in an upright position. Then apply the following:
A standard nasal cannula (NOT the EtCO2 variant).
Set NC @ 15 LPM.
NC will remain in place and running until the ETT is placed.
Non-rebreather mask (yes, over the NC).
Set NRB at the highest LPM available
“Flush” rates are ideal (> 40 LPM).
If 15 LPM is as high as it goes, do it.
A patient who remains hypoxic (oxygen saturations < 93 - 95%) despite maximal passive oxygen delivery is assumed to have shunt physiology, typically. This patient often requires NIPPV (CPAP or BiPAP). It is likely that PEEP is required to obtain appropriate oxygen saturation. This applies to obese patients as well. Pre-Oxygenate these patients as follows:
CPAP or BiPAP; set at parameters your patient care guidelines or protocols call for
Typically, PEEP is started at 5 cmH20
Titrate up, as guidelines indicate
Nasal cannula in place as stated above.
It is possible to maintain a mask seal, most times, with a NC in place.
IF the patient has inadequate respiratory drive, is in need of some manual ventilation support, or apneic, utilize:
Bag-valve mask with a PEEP valve.
@ 15 LPM, or more
Ensure adequate mask seal
Give only gentle breaths
Reduces risk of emesis and aspiration
Do this for 3-5 minutes and get that oxygen saturation as close to 100% as possible. This should give you a “buffer” for the patient’s safety, prolonging the safe apnea and mitigating the harmful effects of hypoxia.
In my opinion, and I'm sure many others agree, you should do everything you can to increase the patient's oxygen saturation prior to inducing apnea. Deliver 100% oxygen, to the best of your ability, to your patient. By doing so, you are decreasing the patient's risk of dysrhythmia, hemodynamic instability, hypoxic brain injury, and just plain old death. If you have made every attempt to increase the patient's oxygen saturations and they still aren't increasing to what we all would call acceptable, move on with your procedure; consider inserting a supraglottic airway, continue ventilating with the bag-valve mask, or go to the knife. If an adverse event is to occur due to hypoxia, we can at least tell ourselves that we took every precaution to reduce the likelihood of this outcome.
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?
Be on the lookout for another blog in this series! The next one will be on apneic oxygenation 😃
Tony Henry, Firefighter, Critical Care Paramedic
There is a ton of good quality content here that some people do not often get educated on or think about after school. One of the big ones that jump right out is the EtCO2 cannula, and how the Oxygen is not actually delivered via the nasal prongs like the traditional NC does.
The point Jared made about knowing how your equipment works really hits the nail on the head for the first half of his blog. It is important to realize some of the data you were educated about is only accurate in ideal conditions, which being in an aircraft or ambulance, generally does not fall under the "ideal conditions" category. I would like to add in, if you are in a setting that offers alternative delivery methods, such as medical air, make sure in the excitement of everything your delivery devices are not accidentally connected to the wrong outputs. (learn from my mistake everyone.)
#5 really hits home as I was discussing this with a student just last week. If you walk in to greet a patient, and they are sitting in an upright or tripod position, what makes you think they are going to want to lay flat when on CPAP. Like Jared said, even if they are apneic, and you are ventilating them, even with mechanically ventilated patients. Keep that head upright slightly and optimize the opportunity for gas exchange and better compliance. Ref-https://ccforum.biomedcentral.com/articles/10.1186/cc13448
For some reason, there has always been some sort of stigma, so to speak, relating to utilizing 2 people on a BVM for an adequate mask seal. If you have the people and space to do so, have one person dedicated to maintaining a mask seal and the other ventilating the BVM @ AN APPROPRIATE RATE AND VOLUME! Single provider proper BVMventilation is one of the hardest skills for all levels of providers to be proficient at, in my opinion. Use the resources you have, even as simple as extra hands.
Brittany Grandfield RN, BSN, CEN, Flight Nurse
I will hand it to Jared for being able to single out, what he thinks, is the most important “P” of the “7 P’s of RSI”. In Jared’s previous blog, Weapon of Choice During Your RSI: Pre-Oxygenation, he points out why pre-oxygenation is so important. For his follow-up to that blog here, he dives into the equipment needed to execute accordingly.
I will start with knowing our equipment, and add to it, by implementing critical thinking skills and how to utilize what we have. Jared noted that a NRB with a two-way valve or "no gasket" does NOT provide 100% FiO2, but only provides upwards of 70% FiO2 at flow rates of 15L per minute. He also added we might not all have a Thorpe Tube flowmeter with flow rates of 40-60L, but instead flow meters capable of 15-25 L. If we note, that to provide 100% FiO2 we must be able to create an adequate seal and/or provide a flow rate above the patient's flow rates. Here is where critical thinking comes into play. If we do not have the equipment to adequately provide a one-way flow, adequate seal, or high enough flow rate, we can combine our equipment to produce enough flow to overcome the patient’s own flow rate. A standard nasal cannula and an NRB combo can help us achieve 100% FiO2 delivery at combined rates set above the patient’s own flow because let’s be honest, who wants to breathe in farts?
I cannot stress enough Jared’s point about positioning our patients. To maximize airflow, the position can make or break our ability to adequately utilize our devices and pre-oxygenate effectively. Two specific patient populations are pregnancy and obesity. Elevating even 20-30 deg HOB can offload abdominal pressure that was displaced onto the thoracic cavity when laying flat.
Pertaining to having to bag our patient with a BVM, a PEEP valve and adequate seal go a long way for pre-oxygenation. Jared notes that providing “gentle breaths” with our BVM reduces the risk of aspiration and emesis. I want to add to this by utilizing a manometer on our BVM. The gastric sphincter opens at pressures of 20-25 cmh20. When utilizing a manometer, we can control the pressure we are delivering with each breath. “Keep it in the green” is my suggestion. Once we exceed the pressure to open the gastric sphincter, not only are we at risk for aspiration and emesis, we are also at risk for distending the belly and placing added pressure on the thoracic cavity and can impede optimal pre-oxygenation. This is specifically important when you have a smaller patient such as a pediatric.
In my experience and through trial and error, knowing our equipment and how to utilize it appropriately goes a long way in pre-oxygenating our patients prior to intubations. Jared did a fantastic job breaking down the equipment we have at our fingertips to utilize for pre-oxygenation.
Jared Patterson, CCP-C, One Rad Medic
Killin' It Since 1989
More From Me:
Weapon of Choice During Your RSI: Pre-Oxygenation: https://www.foamfratblog.com/post/weapon-of-choice-during-your-rsi-pre-oxygenation
Gotta Catch em All - STEMI Equivalents: https://www.foamfratblog.com/post/gotta-catch-em-all-stemi-equivalents
Silly Things Said on the Internet - WPW Blog: https://www.foamfratblog.com/post/silly-things-said-on-the-internet
Difference Between CMV and SIMV: https://www.foamfratblog.com/post/difference-between-cmv-and-simv
5 of My Favorite FOAMfrat Blogs:
Inotropy Isn't "Like Rubber Band": https://www.foamfratblog.com/post/inotropy-isn-t-like-a-rubber-band
Ventilation -- Playing Defence: https://www.foamfratblog.com/post/ventilation-playing-defence
That One Time I Got Kicked Out of My Own Ambulance: https://www.foamfratblog.com/post/that-one-time-i-got-kicked-out-of-my-own-ambulance
Ventilator Waveforms You Gotta Know: https://www.foamfratblog.com/post/2018/12/31/ventilator-waveform-anatomy-the-basics-you-gotta-know
Stop Using Naloxone!: https://www.foamfratblog.com/post/2018/06/09/stop-using-naloxone
Check Out The Rapid Sequence Interrogation (RSI) Podcast:
Brown, C. A., Sakles, J. C., & Mick, N. W. (2018). The Walls manual of emergency airway management. Philadelphia: Wolters Kluwer.
Nickson, C. (2021). Preoxygenation. Retrieved 30 June 2021, from https://litfl.com/preoxygenation/
Pollack, A., McEvoy, M., Rabrich, J., & Murphy, M. (April 3, 2017). Critical Care Transport (2nd ed.). Jones & Bartlett Learning.
Sakles, MD, J., & Brown, MD, C. (2021). UpToDate. Retrieved 10 July 2021, from https://www.uptodate.com/contents/rapid-sequence-intubation-for-adults-outside-the-operating-room?search=Preoxygenation&source=search_result&selectedTitle=2~53&usage_type=default&display_rank=2#H7
Nickson, C. (2020). Preoxygenation. Retrieved 11 July 2021, from https://litfl.com/preoxygenation/
Farkas, J. (2021). Preoxygenation & Apneic Oxygenation Using a Nasal Cannula. Retrieved 10 July 2021, from https://emcrit.org/pulmcrit/preoxygenation-apneic-oxygenation-using-a-nasal-cannula/
Ward, MEd, RRT, J. (2021). High Flow Oxygen Administration by Nasal Cannula for Adult and Perinatal Patients. Retrieved 10 July 2021, from http://rc.rcjournal.com/content/respcare/58/1/98.full.pdf
Weingart, MD, S. (2021). Preoxygenation, Reoxygenation and Deoxygenation. Retrieved 10 July 2021, from https://emcrit.org/preoxygenation/
Christifulli, CCP, FP-C, NRP, T. (2019). The Perils of Preoxygenation. Retrieved 11 July 2021, from https://www.hmpgloballearningnetwork.com/site/emsworld/article/1223307/perils-preoxygenation
Morgenstern, J. (2017). Emergency Airway Management Part 2: Is the patient ready for intubation? - First10EM. Retrieved 11 July 2021, from https://first10em.com/airway-is-the-patient-ready/