Many, many children will suffer from the symptoms of bronchiolitis. Some estimate that it will effect >90% of infants and toddlers under the age of 2 years. We are often at a loss for what to do for some of these babies. They are tachypneic, with retractions and signs of respiratory distress. We want to help them, and when something new and promising comes along we latch onto it. Suffice to say, high flow, has been latched onto in a major way. I have seen it used appropriately, inappropriately, just because care team member were worried that the baby “might get worse,” because that’s what the floor will do anyway so why don’t we just start it, and more. Per some studies HFNC is estimated to be 16 times more expensive than standard nasal cannula.
Therefore, the purpose of this post is to look at the literature on the use of high flow nasal cannula in children with bronchiolitis. This is especially pertinent here in the Spring of 2020 during the COVID-19 pandemic, as there is ongoing discussion about whether or not HFNC is aerosolizing.
How is HFNC being used?
Broadly and without consensus… But in all seriousness, HFNC is used in children with bronchiolitis who have moderate to severe increased work of breathing, refractory hypoxia, and/or episodes of apnea. In general initial flow rates are based on age and patient size, and are typically 1 to 2 L/kg.
What are the proposed physiologic benefits?
Milési et al noted that 2L/kg/minute resulted in mean pharyngeal pressures of >4 cm H2O and improved breathing. in adults (who can keep their mouth closed) there is a linear relationship between flow rate and pharyngeal pressure, from 1-4 cm H2O.
Reduced upper airway resistance
The flow rates of HFNC are greater than that of normal inspiratory pressure. Studies of pulmonary function tests and other dynamic measurements of diaphragm action have been used to assess this.
Washout of dead space in the nasopharynx
It is thought that HFNC washes out expired gas in the nasopharynx, and creates a reservoir of richly oxygenated air.
The warm, humidified air helps too
Dysart et al noted that the warm, humidified air of HFNC reduces oxygen demand in children who have tachypnea and who are rapidly turning over their tidal volume. It may also lead to decreased airway reactiviy and bronchospasm.
Are there any potential harms?
The main risks of HFNC include; gastric distention and resultant poor feeding, barotrauma/pneumothorax, an the increased cost.
What’s the evidence?
Let’s take a look at some of the many recent studies on HFNC in bronchiolitis. I will briefly comment on the significance and impact to the broader conversation to the best of my abilities. Note that there are substantially more observational studies than randomized controlled trials. I also can’t claim to have included every article – I just tried to pick the most relevant ones that will give you a sense of where we have been, and where we are currently. Many studies also compare nasal CPAP to HFNC. I have decided to focus on standard nasal cannula (NC) versus HFNC – since this is the question that arises the most in current EDs.
This is where the bulk of the evidence lies unfortunately.
This retrospective review of 46 patients noted that respiratory scores improved. they also observed better looking X-Rays and that 5/46 needed mechanical ventilation.
This retrospective study compared groups of patients before and after the availability of HFNC between 2006-09 at a single site. The authors noted that “after controlling for age, month of admission, type of respiratory illness, and severity of illness, there was an 83% reduction in the odds of intubation in the PED in patients with HFNC availabel versus not (odds ratio, 0.17; 95% CIl, 0.06-0.50; P = 0.001).” They noted no significant difference in mortality or PICU length of stay after the introduction of HFNC.
Anecdotally the above paper was the first study that lit the HFNC flame in the Pediatric ED.
This retrospective cohort in two hospitals included 498 children under two with bronchiolitis and other respiratory diseases that got HFNC and were seen between June 2011 and September 2012. They concluded that a “diagnosis of bronchiolitis was observed to be protective with respect to intubation (OR, 0.40; 95% CI, 0.17-0.96).” However, this study did not compare HFNC with any other intervention.
This prospective, multicenter observational study included patient data from 16 children’s hospitals between 2001 and 2010. The main take home was that there was a large amount of institutional variability in the use of HFNC and that any conclusions about best practices could not be made.
This was a retrospective, pre-post intervention study of 1,937 children with bronchiolitis seen at a single children’s hospital between 2010 and 2014. They split the study into 2010-12 (pre HFNC) and 2012-14 (after HFNC) and noted that though HFNC use increased, total hospital length of stay (P = .48), PICU length of stay (P = .06), or rate of PICU transfer (P = .97) were not signifincatly different. the authors noted that “there was also no difference in intubation rate or 30-day readmission between the 2 groups.”
Randomized Controlled Trials
This study of 201 Australian children <24 months with moderate bronchiolitis in a single center. The main outcome was time receiving oxygen, and there was no difference in the HFNC and standard cannula groups (20 hours in the HFNC group vs 24 hours in the standard cannula group; hazard ratio, 0.9; 95% CI, 0.7-1.2). The standard nasal cannula did have a higher rate of treatment failure (33%, n=33 for NC versus 14%, n=14 for HFNC0 – as defined by moving to HFNC and/or going to the PICU. Interestingly, both NC and HFNC had the same proportion going to the PICU.
This larger study was also conducted in the southern hemisphere, and included 1,472 children from Australia an New Zealand. Higher flow rates than Keproetes (2 L/kg) were used in infants, Overall the authors noted a higher rate of treatment failure in the standard nasal cannula group (NC – 23% [167 of 733] versus HFNC – 12% [87 of 739]). Again, NC failure meant that the child transitioned to HFNC. 9% of the NC kids went to the PICU