[Use of hypoxic mixture in an infant with congenital heart disease with pulmonary hyperflow and moderate acute bronchiolitis: case report].

Acute bronchiolitis is a major destabilizing factor in infants with congenital heart disease and left-to-right shunt lesions, as it exacerbates pulmonary overcirculation and compromises systemic perfusion. We report the case of a 5-month-old infant with a large ventricular septal defect, patent ductus arteriosus, and severe mitral regurgitation, all with significant hemodynamic repercussions, who developed moderate acute bronchiolitis caused by human metapneumovirus and parainfluenza virus type 3. Despite initial management with continuous positive airway pressure and intravenous vasodilators, the patient showed worsening respiratory distress and systemic hypoperfusion. A high-flow nasal cannula with a hypoxic gas mixture (FiO2 14.5%) was subsequently implemented to increase pulmonary vascular resistance and reduce the left-to-right shunt. This intervention resulted in clinical, gasometric, and radiological improvement. This case highlights the potential role of hypoxic gas therapy as a hemodynamic support strategy in infants with congenital heart disease and bronchiolitis, where controlling pulmonary overcirculation is critical to preserving systemic output. Prospective studies are warranted to further assess its safety and efficacy.