ROX (Respiratory rate-OXygenation) index to predict early response to
high-flow nasal cannula therapy in infants with viral bronchiolitis
Abstract
Introduction High flow nasal cannula (HFNC) is commonly used as
first step respiratory support in infants with moderate-to-severe acute
viral bronchiolitis (AVB). This device, however, fails to effectively
manage respiratory distress in about a third of patients, and data are
limited on determinants of patient response. The respiratory
rate-oxygenation (ROX) index is a relevant tool to predict the risk for
HFNC failure in adult patients with lower respiratory tract infections.
The primary objective of this study was to assess the relationship
between ROX indexes collected before and 1 hour after HFNC initiation,
and HFNC failure occurring in the following 48 hours in infants with
AVB. Method: This is an ancillary study to the multicenter
randomized controlled trial TRAMONTANE 2, that included 286 infants of
less than 6 months with moderate-to-severe AVB. Collection of
physiological variables at baseline (H0), and 1 hour after HFNC (H1),
included heart rate (HR), respiratory rate (RR), fraction of inspired
oxygen (FiO 2), respiratory distress score (mWCAS), and
pain and discomfort scale (EDIN). ROX was calculated as SpO
2/FiO 2 to RR. Predefined HFNC failure
criteria included increase in respiratory distress score or respiratory
rate, increase in discomfort, and severe apnea episodes. The accuracy of
ROX index to predict HFNC failure was assessed using receiver operating
curve analysis. Result: HFNC failure occurred in 111/286 (39%)
infants, and for 56 (50% of the failure) of them within the first 6
hours. The area under the curve of ROX indexes at H0 and H1 were,
respectively, 0.56 (95% CI 0.48-0.63, p =0.14), 0.56 (95% CI 0.49-
0.64, p =0.09). HFNC failure was associated with higher mWCAS score at
H1 (p<0.01) and lower decrease in EDIN scale during the first
hour of HFNC delivery (p = 0.02), but none of the physiological
variables were predictive of HFNC failure. Conclusion: In this
study, neither ROX index, nor physiological variables usually collected
in infants with AVB had early discriminatory capacity to predict HFNC
failure.