Treating children with acute severe asthma who fail to respond to initial high dose inhaled bronchodilators is problematic: use of intravenous agents is inconsistent and side effects are frequent. High flow humidified oxygen (HiFlo) is widely used in respiratory conditions. We carried out a feasibility randomised controlled trial with deferred consent to assess use of early HiFlo in children aged 2 to 11 years with acute severe wheeze not responding to ?burst? therapy (high dose inhaled salbutamol ± ipratropium). Children with PRAM score 5 or more after ?burst? were randomised to commence HiFlo (Vapotherm) or follow standard care. Candidate primary outcomes assessed were: treatment failure requiring escalation, and time to meeting hospital discharge criteria.

Despite disruption by the COVID epidemic, 56 children were randomised across 4 sites (target was 70), and deferred consent was received in 50 children (89%): median (range) age 4 (2-11) years, 32 boys/18 girls. Mean recruitment rate across sites was 1.2 per month. 22 were allocated standard care and 28 early HiFlo. 19/22 (86%) children in standard care and 17/28 (61%) in HiFlo arms experienced treatment failure and needed escalation. Median (range) time to meeting discharge criteria was 37 (1-162) hours in standard care and 29 (7-449) in HiFlo arms. Commonest adverse events (standard care vs HiFlo) included tachycardia (16 vs 19), lactic acidosis (13 vs 9) and hypokalaemia (7 vs 6).

HiFlo in acute severe asthma is a potentially promising intervention and its use is increasing despite lack of evidence. A definitive RCT to assess its effectiveness is required and appears to be feasible.