Randomised controlled studies are needed to evaluate the use of high‐flow nasal cannula therapy in bronchiolitis

Bronchiolitis is the most common infection in infancy that leads to hospitalisation. In a recent two-year study from Finland, 3.7% of all infants under six months of age were admitted to the emergency room for bronchiolitis each year. The majority (70%) were hospitalised, and 6% of those needed intensive care (1). Oxygen and feeding support, if needed, are the cornerstones of bronchiolitis treatment, but the different drugs that have been studied have been ineffective. Administering a warmed, moistened mixture of oxygen and air using a high-flow nasal cannula (HFNC) is a promising new approach for treating infant bronchiolitis. In experimental studies, HFNC treatment has led to beneficial physiological effects on infant bronchiolitis (2–4), and the clinical experiences of using HFNC in neonatology have been good (5). High-flow nasal cannula therapy works by delivering a larger volume of air and oxygen into the nasal passages than standard low-flow oxygen therapy, using a higher flow of humidified and heated gas. Physiological studies have reported that this high flow resulted in more efficient delivery of oxygen to the terminal airways, resulting in reduced work of breathing and improved gas exchange in infant bronchiolitis (2,3). The end-expiratory lung volume and oxygen saturation were reported to be higher, the respiratory rate was lower and less supplementary oxygen was needed when the 8 L/min flow rate was compared to the 2 L/min flow rate in 13 infants (2). Another study of 14 infants showed that the work of breathing, as estimated by diaphragmatic electrical activity and oesophageal pressure, decreased after starting HFNC treatment with a 2 L/kg/ min flow rate (3). Meanwhile, a study of 19 infants reported that nasopharyngeal pressure increased linearly with flow rates up to 6 L/min and that bronchiolitis severity scores improved significantly at this level (6). In this issue of the journal, Milani et al. (7) report the results of their prospective observational study on the use of HFNC therapy in moderate-to-severe infant bronchiolitis treated on the paediatric ward, comparing their results with standard low-flow oxygen administration. The study included 36 infants aged 1.2–5.0 months who needed oxygen support when they were treated on a paediatric ward. The allocation of the patients into the HFNC and standard low-flow treatment groups depended on the availability of the HFNC device. The assessment of the flow rate in the HFNC treatment group was rather complex (L/min = 8 mL/kg*respiratory rate*0.3), but, on the other hand, it was based on the respiratory effort needed. The outcome measures were respiratory rate, the doctors’ clinical assessment of respiratory effort and the ability to feed, which was assessed by nurses who recorded the infants’ milk intake during bottle-feeding or weighed the infants before and after breastfeeding. The improvements in respiratory rate and effort, and the ability to feed, were significantly faster in the infants treated with HFNC than in the controls (7). The median duration of oxygen support was 4 days (interquartile, IQ 3–5 days) in the HFNC group versus 6 days (IQ 5–7 days) in the standard low-flow oxygen group, and the median lengths of hospital stays were 6 days (IQ 5–7 days) versus 9 days (IQ 8–10 days), respectively. Two patients in each group needed to be admitted to the paediatric intensive care unit (PICU). An open, randomised, pilot study of 19 infants treated for bronchiolitis on the paediatric ward that compared HFNC and head-box oxygen supports (8) found that oxygen saturation was higher in the HFNC group at eight and 12 hours, but not at 24 hours onwards. The improvement in respiratory effort was not reported. The total time spent receiving oxygen support and the length of hospital stay did not differ between the groups (8). So far, that study has been the only randomised controlled trial on the effectiveness of HFNC therapy in infant bronchiolitis, but only eight infants were treated with HFNC. As the authors stated, the study did not have significant power to find more differences between the HFNC and control groups. High-flow nasal cannula therapy decreased the need for intensive care in an Australian cohort of 61 infants aged less than 12 months, who were treated for bronchiolitis on a paediatric ward using a 2 L/kg/min flow rate (9). The need for intensive care was 13% in the HFNC group, compared with 31% in the 33 retrospectively collected, matched controls treated with standard low-flow oxygen therapy. In the HFNC group, the responders could be identified from the nonresponders within 60 minutes of treatment, by the decreases in their heart rate and respiratory rate (9). Three retrospective studies evaluated HFNC therapy in infants treated for bronchiolitis in the PICU. In two studies,