Sunday, March 8, 2015

High-flow nasal cannulas: Not yet ready for ED use.

What is high-flow nasal cannula (HFNC) therapy, and, more importantly, does it work? A recent segment on EM:RAP went into a fair amount of detail about the putative mechanism, so I’ll leave that alone.

What that segment left out, though, was any discussion of the published evidence pointing to the benefit of HFNC. And indeed, while there are a lot of anecdotal reports and personal testimonials, the actual data hasn’t been clearly discussed. Here’s a quick review of what we currently know.

1. Preterm infants

Although the “diet-PEEP” argument would suggest that HFNC might have a large role in tiny patients, it isn’t clear that HFNC helps prevent intubation in preemies. A Cochrane review suggested that using HFNC post-extubation, instead of CPAP, might lead to higher re-intubation rates. An RCT that was conducted after that review, however, found that HFNC was roughly equivalent to nasal CPAP for respiratory support in this age group. Data from other recent trials haven’t been as convincing, though, and many neonatologists still find the evidence “insufficient” to use HFNC in place of more established therapies

2. Infants

It may help prevent intubation of little kids with bronchiolitis, although the data is weak. The two most relevant studies were retrospective chart reviews, using a before-and-after design, looking at overall rates for intubation in the time period after HFNC was introduced to the pediatric service. Nonetheless, McKiernan found that intubation rates for bronchiolitis dropped from 23 % to 9%, and Schibler found the rate plummeted for 37% to 7%!
McKiernan 2010
This may end up being one of the best-supported roles for HFNC, and high-quality studies are in progress that could help clarify the issue.

3. Adults

The initial trials in adults have demonstrated modest improvements in oxygenation, but haven't studied patient oriented-outcomes. For example, one study found that oxygenation mildly increased after HFNC initiation, but no control group was used.

Sztrymf 2012

In one controlled trial, versus face mask, fewer desaturations were seen with HFNC. Despite this, there was no statistical difference in the use of rescue CPAP/BiPAP. A few other studies have further noted that HFNC seems to be more comfortable than CPAP.

A single-author review, otherwise very bullish on HFNC therapy, conceded: “although some clinicians may have the impression that in some instances, use of HFNC has avoided intubation, this has not been shown in a controlled trial.”

The largest current review on the use of HFNC concludes that (my emphasis):
“While theoretical advantages exist over standard nasal cannula and face mask oxygen, current evidence does not definitively demonstrate superiority to other methods of respiratory support. Few studies have focused on clinical outcomes beyond common respiratory parameters. Given the potential lack of consistency of positive pressure generated with current HFNC systems, NIV such as CPAP and bilevel positive airway pressure should still be considered first line therapy in moderately distressed patients in whom supplementation oxygen is insufficient and when a consistent positive pressure is indicated.”

Bringing it home!

Being an “early-adopter” is cool – if you’re lining up to get the new iPhone or Zune! In medicine, however, it doesn’t often pay to jump on a bandwagon before the data is in. (Want to buy some Xigris cheap?) We are being encouraged to try a new therapy that uses proprietary (proprietary = $) devices, with soft indications, scant evidence, but with touted outcomes such as “improved comfort,” instead of mortality or rates of intubation. We should be cautious.

Particularly concerning is the uncritical enthusiasm for the use of this device in situations that either clearly call for other therapies, or for no therapy. For example, some describe the utility of HFNC in patients who are “extremely hypoxic,” but there is little evidence that HFNC improves outcomes in this population.

HFNC is probably more useful for precisely titrating FIO2 in the (mythical?) CO2 retainer. But if there is a concern about the PaCO2, why not use a proven therapy like NPPV that we know saves lives?

Lastly, some clinicians promote the use of HFNC for CHF, since there is (wink, wink) a “PEEP component,” but that’s a patient who needs CPAP or BiPAP as well, since we already have proven a mortality benefit in that population as well.

Sure, you can relax, talk with family, and eat while wearing HFNC, but if you are so dead set on wolfing down a sandwich, you probably don’t need an expensive, unproven therapy. You need 2 liters per minute, and a floor bed!