Children with uncontrolled asthma and significant reversibility might show hypoxaemia.

Asthmatic children free of exacerbation with airway obstruction may have low partial pressure of oxygen (PaO) which can be a marker for future risk, but PaO is scarcely measured during pulmonary function testing. We prospectively included asthmatic children with airway obstruction referred for pulmonary function testing, including blood gas analysis (n = 51). Hypoxaemia, defined as a value lower than - 2 z-score, was present in 15 (29%) children, and 37 (72%) children had a significant reversibility after bronchodilator administration. The multivariable model showed a positive influence of baseline forced expiratory volume in 1 s (FEV) on PaO (β coefficient 0.69, [95% CI: 0.07; 1.30]; P = 0.03), whereas uncontrolled asthma and FEV reversibility negatively influenced it (β coefficient - 1.59 [95% CI: - 2.74; - 0.44]; P = 0.01; and - 0.07 [95% CI: - 0.13; - 0.02]; P = 0.01, respectively). As a consequence, children with uncontrolled symptoms of asthma and FEV reversibility ≥ 12% were significantly more at risk of having hypoxaemia compared to children with well/partly controlled asthma or no significant reversibility of FEV.Conclusion: Among obstructive asthmatic children without current exacerbation, hypoxaemia is more likely to be seen in children with uncontrolled asthma and a significant post-bronchodilator FEV reversibility, in favour of different pathophysiology and treatment requirements of their airway obstruction.What is Known:• Recommendations are to treat asthmatic children in order to control respiratory symptom and maintain normal pulmonary function.• Asthmatic children free of exacerbation may have different pathophysiology for airway obstruction (central, peripheral, inflammatory, spasticity, remodelling) and should be treated according the pathophysiology of their airway disease.What is New:• In obstructive asthmatic children free of current exacerbation, the presence of hypoxaemia (ventilation-perfusion mismatch) is influenced by asthma control and post-bronchodilator reversibility, independently of the level of baseline airway obstruction.• The presence of hypoxaemia in obstructive asthmatic children free of current exacerbation can be highly suspected by the composite index "uncontrolled asthma + FEVreversibility ≥ 12%" which may guide treatment.