The Rule of 2s

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Nurses Edition Commentary

Mizuho Spangler, DO, Lisa Chavez, RN, and Kathy Garvin, RN

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Brooks W. -

Great review on oxygenation and ventilation, always appreciated!

I wonder, however, if the use of the high-flow nasal cannula (HFNC) is being presented too uncritically. Both Dr Mallemet and Dr Sacchetti (in Feb 2014) have enthusiastically described the use of this new and not-free device, but we haven't heard a more skeptical point of view.

I won't portray myself as a critical-care expert or airway guru, but it seems like the literature supporting the use of HFNC in adults, and even in non-neonate children, is pretty darn weak. Sure, there's a postulated "weak PEEP" effect, but it seems a little premature to give this device equal billing with standard non-invasive ventilation, which actually has Cochrane-level evidence behind it.

Hope this doesn't come off as a rant. EM:RAP has always been willing to "teach the controversy;" maybe someone could deliver a skeptical comment of HFNC?

Alfred S., M.D. -

Dr. Brooks:

Your use of High Flow Nasal Cannula depends on whether you are an early adopter of new technologies or one of the late majority. Personally, I don't wait until multiple randomized trials are completed before exploring new techniques or therapies. I will try new ideas and compare them to my prior clinical experiences. (I know all that nonsense about confirmation biases clouding my judgement, but still believe I can make some valid observations) This is essentially what we did when we published the first ED case series on the use of BiPAP in the ED way back in the early 90's.

Anyway, regarding HFNC, it is awesome. I have been using it more and more with tremendous success. Need to pick the right patients and will be glad to discuss it with you. Also, it is not that expensive.

However, I will disagree with the mechanism of aciton, it does not work by providing low dose positive airway pressure. I have an upcomming interivew on EMRAP with a respiratory physiologist on this subject. It really works by mimicking the breathing of a new born infant and eliminates the anatomic dead space.

Once you wrap you mind around this you can see how it is the better treatment for specific types of respiratory distress patients.

To quote a rather famous antacid commercial "Try it you'll like it."

Alfred S., M.D. -


Nice discussion on Non-invasive Ventilation. Just a couple of comments on a different practice style.

Regarding beginning patients on BiPAP. In our shop, for CHF and other acutely struggling patients we go directly with IPAP/EPAP of 20/15, 100
% oxygen, no titration. We simply tell the patients this mask is going to make them feel immediately better after 5 breaths then either a doc or a nurse places and holds the mask in place. No straps yet. Having been told they need to take 5 breaths seems to set an expectation and in fact they realize that after a few breaths they are breathing better. We get no struggling, no fighting, no arguments. Maybe this technique works for us because the staff effectively conveys to the patient confidence in the BiPAP and that there is no room for discussion. Whatever the reason, we have over a 95% success rate with this approach and have patients out of respiratory distress in 2-3 minutes.

One other point, regarding BPAP vs BiPAP, I believe BiPAP is now considered a ventilation therapy and not simply a proprietary device. It is a description of Bilevel Positive Airway Pressure, so you can say it or write it as a management technique and not just Respironic's machine.

Keep up the good work.



Haney M. -

Thanks for weighing in Dr. Sacchetti.

Dr. Brooks, with respect to the evidence for HFHNC I agree that there is not a huge amount of "high quality randomized control trials" to support it's use, but after using it on patients, I have to say it works and works well.....not in every patient, but in a lot of patients. Anyone who does not believe it should give it a try on a patient and they may become a believer. There are proprietary manufacturers for HFHNC, but a HFHNC device can also be "built" by your respiratory therapists with spare equipment already in the hospital; in fact we routinely used a "homemade" HFHNC device until the proprietary devices were marketed.

Dr. Sacchetti, with respect to the exact mechanism of HFHNC, I cannot find any "high-quality" evidence supporting the precise physiologic mechanism of how it works in adults. I agree that there is definitely a component of deadspace washout that happens in the nasopharynx and this contributes to the benefit (and possibly other mechanisms such as the venturi effect....). But I do believe that there at least some benefit via the positive pressure effect secondary to the higher flow rate of the device and this has been shown to be correlated with mild levels of PEEP. Nonetheless, I look forward to your upcoming talk with the respiratory physiologist and hope there are references referring to the true physiologic mechanisms for HFHNC.

Thank you for your fantastic pearls Dr. Sacchetti, and for replying back.


George D., M.D. -

Hi Haney

Something we started to do at our place to help with the titration of pressures is incorporating something that people already know and use in intubated patients- the ARDSnet PEEP/FiO2 scale and tidal volumes.
It also has the inadvertant benefit of teaching people used to Assist Control (Volume Control for Aussies) how they use Pressure Control if they ever needed to do so for a kid.


Haney M. -

Hi George,

This is great and I'll give it a try on my next patient. Not only like the idea, but also a great way to standardize things so everyone is speaking the same "respiratory" language, thus minimizing variations in practice.

Thank you for showing me this and I'll let you know how it goes.


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It is Hard to Breathe When Your Vocal Cords Don’t Work! Full episode audio for MD edition 251:25 min - 293 MB - M4AEM:RAP 2015 Février Résumé en Francais Français 60:40 min - 50 MB - MP3EM:RAP 2015 February Canadian Edition Canadian 14:10 min - 12 MB - MP3EM:RAP 2015 Febrero Resumen Español Español 95:30 min - 76 MB - MP3EM:RAP 2015 February Aussie Edition Australian 88:33 min - 81 MB - MP3EM:RAP 2015 February MP3 279 MB - ZIPEM:RAP 2015 February Summary 2 MB - PDFEM:RAP 2015 Español Febrero Summary 939 KB - PDFEM:RAP 2015 February:Board Review Answers 375 KB - PDFEM:RAP 2015 February:Board Review Questions 374 KB - PDF