Background: Tracheostomies in children are associated with significant morbidity, poor quality of life, excess healthcare costs, and excess mortality. The underlying mechanisms facilitating adverse respiratory outcomes in tracheostomised children are poorly understood. We aimed to characterise airway host defence in tracheostomised children using serial molecular analyses. Methods: Tracheal aspirates, tracheal cytology brushings, nasal swabs and stool samples were prospectively collected from children with a tracheostomy and controls. Transcriptomic, proteomic, and metabolomic methods were applied to characterise the impact of tracheostomy on host immune response and the airway microbiome. Results: Children followed up serially from the time of tracheostomy up to three months post-procedure (n=9) were studied. A validation cohort of children with a long-term tracheostomy was also enrolled (n=24). Controls (n=13) comprised children without a tracheostomy undergoing bronchoscopy. Tracheostomy was associated with new, rapidly emergent and sustained airway neutrophilic inflammation, superoxide production and evidence of proteolysis when compared with controls. In contrast, reduced airway microbial diversity was established pre-tracheostomy and sustained thereafter. Conclusions: Childhood tracheostomy is associated with rapidly emergent and persistent airway neutrophil recruitment and activation, with sustained proteolysis and superoxide generation. These findings suggest neutrophil recruitment and activation as potential exploratory targets in seeking to prevent recurrent airway complications in this vulnerable group of patients.

MB: Not related to this work: investigator-led research grants from Pfizer and Roche Diagnostics; speaker fees paid to Newcastle University from Novartis, Roche Diagnostics and TEVA. Travel expenses to educational meetings Boehringer Ingelheim and Vertex Pharmaceuticals. Other authors: None.

This study was funded by; Academy of Medical Sciences Grant SGL020\1003; Newcastle University Wellcome Trust Institutional Strategic Support Fund; Newcastle Hospitals Charity; SHIELD consortium; Barbour Foundation.

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Ethics committee of Yorkshire & The Humber (Reference 19/YH/0061) gave ethical approval for this work

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