Is Treatment with a High Flow Nasal Cannula Effective in Acute Viral Bronchiolitis? A Physiologic Study

Purpose: The high flow nasal cannula (HFNC) has recently been proposed to support infants with respiratory syncytial virus (RSV)-related respiratory distress. However, in this disease, no physiologic data are currently available on the effects of this device. We assessed the capacity of HFNC to generate positive airway pressure, as well as the resulting effects on breathing pattern and respiratory effort.

Methods: Twenty-one infants less than 6 months old with acute RSV bronchiolitis were studied prospectively in the pediatric intensive care unit of a university hospital. Pharyngeal pressure (PP) and esophageal pressure (Pes) were measured simultaneously at four increasing flows of 1, 4, 6 and 7 L/min delivered through HFNC.

Results: The PP was correlated with flow rate (r = 0.65, p ≤ 0.0001), reaching mean and end-expiratory values of, respectively, 4 (95% CI 3-5) cmH₂O and 6.5 (95% CI 5-8) cmH2O at 7 L/min. A flow ≥2 L/kg/min was associated with the generation of a mean pharyngeal pressure ≥4 cmH₂O with a sensitivity of 67 %, a specificity of 96 %, a positive predictive value of 75 %, and a negative predictive value of 94.5%. Only flows ≥6 L/min provided positive PP throughout the respiratory cycle. From baseline to maximal flow rate, breathing frequency (p < 0.01), T i/T tot (p < 0.05), Pes swing (p < 0.05) and PTPesinsp/min (p < 0.01), an index of respiratory effort, were reduced.

Conclusions: HFNC with a flow rate equal to or above 2 L/kg/min generated a clinically relevant PP, with improved breathing pattern and rapid unloading of respiratory muscles, in young infants with acute RSV bronchiolitis.