Many patients breathing oxygen from nasal cannulas do not receive the benefit of the oxygen flow from both cannula prongs. This can be the result of displacement of the cannula so that one or both prongs are not directed into the nasal passages or the result of pathologic or iatrogenic obstruction of a nostril. We studied the effect on the Pao2 of healthy subjects' breathing oxygen from only one of the two prongs of a standard nasal oxygen cannula. Displacement to the side so that only one prong was in a naris resulted in a mean drop in Pao2 of 22 mm Hg compared to the Pao₂ achieved when the cannula prongs were properly placed in both nares. Such a drop in Pao₂ could result in hypoxemia in some patients. These results may have implications in patients with pathologic or iatrogenic nasal obstruction as well as in patients whose nasal cannula prongs have been misplaced. Care should be taken to assure proper placement of nasal oxygen cannulas at all times. In some patients, a cannula with a single prong, or an oxygen mask, may be more efficacious than the standard double-pronged cannula commonly used.
