Effect of flow rate on the end-expiratory lung volume in infants with bronchiolitis using high-flow nasal cannula...

To evaluate the effects of four flow rates on the functional residual capacity (FRC) and pulmonary ventilation distribution while using a high-flow nasal cannula (HFNC).

Our hypothesis is that flow rates below 1.5 L·kg^-1 ·min^-1 lead to FRC loss and respiratory distress.

A single-center, prospective clinical study.

Infants diagnosed with acute viral bronchiolitis were given HFNC.

Through a prospective clinical study, the effects of four different flow rates, 2.0, 1.5, 1.0, and 0.5 L·kg^-1 ·min^-1 , on FRC and the pulmonary ventilation pattern were evaluated using electrical impedance tomography. The impedance variation (delta Z), end-expiratory lung volume (EELZ), respiratory rate, heart rate, respiratory distress score, and saturation/fraction of inspired oxygen ratio (SpO₂ /F_I O₂ ), were also evaluated at each flow rate.

Among the 11 infants included, There was a decrease in respiratory distress score at a flow rate of 1.5 L·kg^-1 ·min^-1 (*p = 0.021), and at a flow rate of 2.0 L·kg^-1 ·min^-1 (**p = 0.003) compared to 0.5 L·kg^-1 ·min^-1 . There was also a small but significant increase in SpO₂ /FiO₂ at flow rates of 1.5 (*p = 0.023), and 2.0 L·kg^-1 ·min^-1 (**p = 0.008) compared to 0.5 L·kg^-1 ·min^-1 . There were no other significant changes in the clinical parameters. In the global EELZ measurements, there was a significant increase under a flow rate of 2.0 L·kg^-1 ·min^-1 as compared to 0.5 L·kg^-1 ·min^-1 (p = 0.03). In delta Z values, there were no significant variations between the different flow rates.

The ∆EELZ increases at the highest flow rates were accompanied by decreased distress scores and improved oxygenation.