Description and Validation of a Novel Score (Flow Index) as a Clinical Indicator of the Level of Respiratory Support to Children on High Flow Nasal Cannula

This study's objective was to describe and validate flow index (flow rate × FiO /weight) as a method to report the degree of respiratory support by high flow nasal cannula (HFNC) in children. We conducted a retrospective chart review of children managed with HFNC from January 1, 2015 to December 31, 2019. Variables included in the flow index (weight, fraction of inspired oxygen [FiO ], flow rate) and outcomes (hospital and intensive care unit [ICU] length of stay [LOS], escalation to the ICU) were extracted from medical records. Max flow index was defined by the earliest timestamp when patients FiO × flow rate was maximum. Step-wise regression was used to determine the relationship between outcome (LOS and escalation to ICU) and flow index. Fifteen hundred thirty-seven patients met the study criteria. The median first and maximum flow indexes of the population were 24.1 and 38.1. Both first and maximum flow indexes showed a significant correlation with the LOS ( = 0.25 and 0.31, 20 and maximum flow index >59.5 had increased odds ratio of escalation to ICU (odds ratio: 2.39 and 8.08). The first flow index had a negative association with rapid response activation. Flow index is a valid measure for assessing the degree of respiratory support for children on HFNC.