The "28%" Venturi mask is effective in correcting hypoxemia in 60% of patients with acute respiratory failure. Patients with an initial oxygen tension of less than 30 mm Hg are unlikely to achieve adequate oxygenation with this mask delivering 28% oxygen and probably should be treated initially with 35% oxygen. Although mean increases in oxygen tension are fairly constant, the variability from patient to patient is more marked among acutely ill patients and probably results from the variable degree of anatomic right-to-left shunting present. There is little danger of precipitating acute CO2 narcosis with the 28% Venturi mask, and in the majority of patients it is a satisfactory device for oxygen therapy in acute respiratory failure.
Bedon GA, Block AJ, Ball WC. The "28%" Venturi Mask in Obstructive Airway Disease. Arch Intern Med. 1970;125(1):106-113. doi:10.1001/archinte.1970.00310010108010