High flow systems for apnoeic oxygenation

nascaniconApnoeic oxygenation during laryngoscopy via nasal prongs has really taken off in the last couple of years in emergency department RSI, and is associated with decreased desaturation rates in out-of-hospital RSI.

More effective oxygenation and a small amount of PEEP can be provided by high flow nasal cannulae with humidified oxygen (HFNC)

A logical step in the progression of this topic is to consider HFNC for apnoeic oxygenation, and Reuben Strayer wrote about this nearly three years ago.

In a Twitter conversation today, Dr Pete Sherren highlighted a new article describing its use in anaesthesia for patients with difficult airways. This is labelled Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE). A reply from Dr Neil Brain points out that when used in kids, the bulkiness of the apparatus may get in the way of bag-mask ventilation (if that becomes necessary).

But does HFNC apnoeic oxygenation confer any advantages over standard nasal cannulae?

In an apnoeic patient, 15l/min via standard cannulae should fill the pharyngeal space with 100% oxygen, and you can’t improve on 100%.

HFNC provide some continuous positive pressure, but this may be cancelled by the necessary mouth opening for laryngoscopy.

One issue with apnoea is of course a rise in carbon dioxide with consequent acidosis. The authors of the THRIVE paper (abstract below) point out that in previous apnoeic oxygenation studies, the rate of rise of carbon dioxide levels was between 0.35 and 0.45 kPa/min (2.7-3.4 mmHg/min), whereas with THRIVE the rise was 0.15 kPa/min (1.1 mmHg/min). They suggest that continuous insufflation with high flow oxygen facilitates oxygenation AND carbon dioxide clearance through gaseous mixing and flushing of the deadspace.

So should we switch from standard nasal cannula to high flow cannulae for apnoeic oxygenation? I think not routinely, but perhaps consider it in patients:

(1) with pressure-dependent oxygenation (eg. ARDS) although I’m not sure any CPAP effect would be sustained during laryngoscopy


(2) in patients with significant acidosis in whom a significant rise in carbon dioxide could be detrimental (eg. diabetic ketoacidosis).

I look forward to reading more studies on this, and to hearing from anyone with experience of this technique in the comments section.

Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE): a physiological method of increasing apnoea time in patients with difficult airways.
Anaesthesia. 2014 Nov 10. doi: 10.1111/anae.12923. [Epub ahead of print]

Emergency and difficult tracheal intubations are hazardous undertakings where successive laryngoscopy-hypoxaemia-re-oxygenation cycles can escalate to airway loss and the ‘can’t intubate, can’t ventilate’ scenario.

Between 2013 and 2014, we extended the apnoea times of 25 patients with difficult airways who were undergoing general anaesthesia for hypopharyngeal or laryngotracheal surgery. This was achieved through continuous delivery of transnasal high-flow humidified oxygen, initially to provide pre-oxygenation, and continuing as post-oxygenation during intravenous induction of anaesthesia and neuromuscular blockade until a definitive airway was secured. Apnoea time commenced at administration of neuromuscular blockade and ended with commencement of jet ventilation, positive-pressure ventilation or recommencement of spontaneous ventilation. During this time, upper airway patency was maintained with jaw-thrust.

Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) was used in 15 males and 10 females. Mean (SD [range]) age at treatment was 49 (15 [25-81]) years. The median (IQR [range]) Mallampati grade was 3 (2-3 [2-4]) and direct laryngoscopy grade was 3 (3-3 [2-4]). There were 12 obese patients and nine patients were stridulous. The median (IQR [range]) apnoea time was 14 (9-19 [5-65]) min. No patient experienced arterial desaturation < 90%. Mean (SD [range]) post-apnoea end-tidal (and in four patients, arterial) carbon dioxide level was 7.8 (2.4 [4.9-15.3]) kPa. The rate of increase in end-tidal carbon dioxide was 0.15 kPa.min(-1) .

We conclude that THRIVE combines the benefits of ‘classical’ apnoeic oxygenation with continuous positive airway pressure and gaseous exchange through flow-dependent deadspace flushing. It has the potential to transform the practice of anaesthesia by changing the nature of securing a definitive airway in emergency and difficult intubations from a pressured stop-start process to a smooth and unhurried undertaking.

8 thoughts on “High flow systems for apnoeic oxygenation”

  1. I have concerns about mask seal even in adults. Cost is also sig. higher. If the patient is already on high-flow device, I would probably leave it on for intubation.

  2. Strikes me that standard nasal specs are available in most locations and allow a seal with face mask.

    Whereas high flow require just that, are bulky…and benefit of minimal PEEP lost once mouth opened.

  3. This is rant-ish length, I realize. HFNC-mania is sort of a pet peeve of mine….

    Any new study involving a HFNC involves the word “may” a lot. it may provide some PEEP, it may blunt the CO2 increase, it may prevent intubation, or may help wean. As Jerry Hoffman says, “just replace each ‘may’ with ‘may not!'”

    The OptiFlow (as one example of HFNC) is a proprietary ($$) device, with soft indications, scant evidence, but with overly-hyped outcomes such as “improved comfort,” instead of mortality or rates of intubation. This is a device looking for market share, not a therapy to ask for on your next shift.

    Particularly concerning is the uncritical enthusiasm of many for the use of this device in situations that either clearly call for other therapies (or for no therapy). For example, the authors describe the benefit of HFNC for blunting the rise in PCO2. Leaving alone the weak historical-control evidence, if there is a concern about the PaCO2, why not use a proven therapy like NPPV?

    Similarly, if you need some positive pressure (e.g. ARDS), why choose the device with just possible, and quite mild, “PEEP component.” That’s a patient who needs CPAP/BiPAP.

    Review articles about HFNC have concluded that “current use appears to be without clear criteria and mostly based on individual preference. Furthermore, “that “HFNC has NOT been demonstrated to be equivalent or superior to non-invasive positive pressure ventilation, and further studies are needed to identify clinical indications for HFNC in patients with moderate to severe respiratory distress.”

  4. Hi! Thanks for great post. Struggled with a patient yesterday with ARDS whom we had to intubate. Best pre intubation sats on nasal prongs and non rebreather mask was 75%. So inserted size 5 ETT (cut) as modified Nasopharyngeal airways and attached oxygen tubing with flow rate at 10l/min, Sats increased to 100%. Intubated with the modified “nasopharyngeal airways” in place. No DESAT 🙂
    Best wishes
    Cape Town, South Africa

  5. For the reason of BVM mask seal mentioned by Scott and others, HFNC during intubation seems unwise. Making a big sacrifice on ability to reoxygenate for a theoretical and small incremental improvement in preoxygenation/apneic oxygenation just doesn’t make sense to me. I say big sacrifice because if your plan is to rip off HFNC if you need to bag mask, you lose that continuous flow of O2 which allows you to give more effective PEEP when combined with a PEEP valve. A PEEP valve + regular Nasal prongs will give more PEEP to your ARDS pt than HFNC ever could. If a pt I had on Optiflow needed a tube I certainly would switch to simple NP for intubation.

  6. Used it several times on ICU – can effect mask seal. Trailing it in ED so will see how we get on with it.

  7. I posted a blog on this a little while ago (http://www.pulmcrit.org/2014/07/preoxygenation-apneic-oxygenation-using.html). Have used high-flow nasal oxygen via standard catheters (by cranking them past 15 liters/min) as well as proprietary devices (OptiFlow). It works well both ways. My last case involving nasal high flow (via a standard nasal cannula) was a patient with massive GI bleed and active hematemesis. We preoxygenated him on his side while he was actively vomiting blood… when he stopped vomiting we paralyzed him, quickly turned him on his back (with the nasal cannula on) and performed RSI. Saturation nearly 100% throughout. This is a great way to preoxygenate someone when the only thing you have to work with is the nose. As discussed in the blog I don’t think this is for everyone, but it has helped me out of a couple tight spots!

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