When assessing a patient who is hypoxic, monitors to measure pulse oximetry, electrocardiogram, and blood pressure should be placed while providing supplemental oxygen. The mental status should be observed and the chest should be auscultated to ensure that the airway is patent, that the lungs are clear, and that spontaneous respiratory efforts are adequate. Quickly check areas to rule out include obstruction either via collapse of the soft tissues or via a foreign object (such as a mucous plug or vomitus), stridor, and bronchospasm. These reasons for hypoxia should be ruled out and addressed before significant improvement is seen with supplemental oxygen.

In certain patient populations, the benefits of supplemental oxygen must be weighed with the potential risks. Neonates, especially expremature infants younger than 44 weeks’ postconceptual age, are at risk of developing retrolental fibroplasia (otherwise known as retinopathy of prematurity). It is suggested that PaO₂ does not rise above 80 torr in this population. Supplemental oxygen in patients with certain congenital heart lesions (hypoplastic left heart syndrome, single ventricle physiologies, ventricular septal defect, patent ductus arteriosus) will cause an increase in alveolar oxygen tension and may compromise the balance between pulmonary and systemic flow. Patients taking certain chemotherapeutic drugs, such as bleomycin, may be prone to oxygen toxicity and pulmonary fibrosis.

Nasal cannulae fall under the category of low-flow systems. They are used to provide a low concentration of oxygen to the patient. The actual FIO₂ delivered depends on oxygen flow, nasopharyngeal volume, and inspiratory flow. FIO₂ roughly increases 1% to 2% above 21% per liter of oxygen flow in a normally breathing adult. So, at oxygen flows of 3 to 4 L/min, nasal cannulas can deliver an FIO₂ of 30% to 35%. An FIO₂ of 40% to 50% can be attained with flows of >10 L/min. In infants, FIO₂ of 0.35, 0.45, 0.6, and 0.68, with flows of 0.25, 0.5, 0.75, and 1 L/min, respectively, can be attained.