INTRODUCTION
Acute viral bronchiolitis (AVB) is a leading cause of lower respiratory
tract infection and hospitalization in young infants, notably those aged
less than 1 year [1]. Management of moderate-to-severe AVB is based
on respiratory support, with as the first step administration of a
heated and humidified mixture of air and oxygen with highâflow nasal
cannula (HFNC) [2]. While several studies have confirmed HFNC
effectiveness to reduce the work of breathing in AVB [3-5], failure
occurs in 30-40% of these patients [6-8]. In these infants,
evolving respiratory failure requires escalation in therapeutic
measures, including transition to continuous positive airway pressure
(CPAP), then if necessary to noninvasive ventilation or intubation
[9].
Early identification of patients who are most likely to fail with HFNC
is critical for care organization in the pediatric emergency department
[10]. Indeed, these infants will need to be referred to a pediatric
intensive care unit, necessary for the monitoring of any non-invasive
ventilation technique including CPAP and bilevel positive airway
pressure, while those who will improve with HFNC can potentially be
transferred to a general pediatric ward [11]. Currently, some
patient characteristics have been individualized as predictors of
respiratory deterioration, notably younger age or initial severity
[12, 13]. However, neither isolated physiologic parameters, such as
respiratory rate (RR), fraction of inspired oxygen
(FiO2), or venous/capillary partial pressure of carbon
dioxide (pvCO2), nor clinical scales that incorporate
different vital signs have demonstrated a consistent association with
the risk of HFNC failure and are discriminating enough to be used as
triage tools [14-18].
Recently, Roca et al. developed a tool to assess the risk for
HFNC failure in adult patients with hypoxemic acute respiratory failure
[19]. ROX (Respiratory rate-OXygenation) index corresponds to the
ratio of patient oxygenation, which has been associated to HFNC success,
over RR, which has been associated to HFNC failure. Subsequent studies
confirmed it was a good predictor of HFNC failure in lower respiratory
tract infections, including those caused by virus [20, 21]. In
pediatric patients with acute respiratory failure, ROX index application
24 and 48 hours after hospital admission also appeared a good marker for
predicting the risk of HFNC failure [22]. In the specific context of
AVB in <2 years infants managed in a pediatric emergency
department, patients with ROX index in the lowest quartile at HFNC
initiation were three times more likely to require CPAP compared to
those in the highest quartile [23]. The single-center nature of this
study, with lack of standardization for failure criteria, incited to
test the relevance of ROX index in an homogeneous population of
<6 months infants requiring HFNC for severe AVB, recruited in
the framework of a multicenter study with predefined HFNC failure
criteria [24].
The primary objective of this study was to assess the relationship
between ROX index collected early (i.e. before HFNC initiation
and 1 hour after), and HFNC failure occurring in the following 48 hours
in patients admitted for severe AVB.