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 patie