Heated High Flow Nasal Cannula Flow Rates in Critical Pediatric Asthma: An Observational Cohort Study

Objective: Heated high flow nasal cannula (HHFNC) use in pediatric critical asthma is rising despite concerns regarding its ability to effectively deliver nebulized medications to the lower airway. We aim to measure the association of low versus high HHFNC flow rates for delivery of continuously inhaled short acting beta agonist (cSABA) on clinical outcomes in the Pediatric Intensive Care Unit (PICU).Methods: This is a retrospective cohort study investigating PICU patients admitted with critical asthma who were prescribed HHFNC for cSABA delivery. Patients were divided into two groups based on the average flow rate used to deliver cSABA: low flow (≤5 L/min) versus high flow (>5 L/min). Outcomes including total duration of cSABA, total duration of noninvasive respiratory support (HHFNC, continuous (CPAP) and bilevel (BPAP) positive airway pressure), PICU LOS, and hospital LOS were explored. Data were analyzed by Wilcoxon-Rank Sum, Chi-squared and Fisher’s Exact tests.Results: 112 patients were included. Patients in the low flow group (n = 56) had a median HHFNC flow rate of 4.0 L/min (IQR 3.9-4.0) versus patients in the high flow group (n = 56) at 9.6 L/min (IQR 7.0-15.0; p < 0.001). Pediatric Asthma Severity Scores (PASS) were similar (p = 0.095). The low flow group had significantly shorter total duration of cSABA (p = 0.048), shorter duration of noninvasive respiratory support (p = 0.0234), and shorter PICU (p < 0.001) and hospital (p = 0.0063) LOS.Conclusions: Low HHFNC flow rates for cSABA delivery are associated with shorter durations of cSABA, noninvasive respiratory support, PICU and hospital LOS.