Estimating inspired oxygen concentration delivered by nasal prongs in children with bronchiolitis

The inspired oxygen concentration (FiO(2)) is an important criterion for assessing the severity of bronchiolitis. Oxygen delivery by nasal prongs is a measure of oxygen flow, but not FiO(2). We aimed to determine whether FiO(2) of oxygen delivered by nasal prongs could be predicted from nasal flow by relating arterial oxygen concentrations achieved with prongs to those achieved via head box in children with bronchiolitis.

This is a pilot study conducted at a tertiary referral paediatric hospital. We studied hospitalised children less than 24 months old requiring supplemental oxygen because of bronchiolitis, an acute viral lower respiratory tract infection. Children admitted to the intensive care unit, and those with congenital cardiac disease or recent bronchodilator use were excluded. Subjects were studied in nasal prong, then head box oxygen. Arterial oxygen concentration was measured by a transcutaneous probe (tcPO(2)). Oxygen flows by nasal prongs and FiO(2) by head box were adjusted to achieve similar tcPO(2) readings. FiO(2) values were plotted against oxygen flow rates based on matching tcPO(2).

We recorded tcPO(2) across a satisfactory range of values in eight children. TcPO(2) increased with increasing FiO(2) and nasal oxygen flow, but at variable rates between subjects. FiO(2) increased with increasing nasal oxygen flow, but this relationship was highly variable.

In this study, it was not possible to estimate FiO(2) reliably from nasal oxygen flow rates in children with bronchiolitis. Nasal prong oxygen flow rates should be used with caution when assessing the severity of bronchiolitis in children.