While the ability of high-flow nasal cannula to achieve apneic oxygenation is well established, the ability to remove carbon dioxide is less clear. The recent investigation by Riva and colleagues on the issue, in which various flow rates were examined during apneic periods, interested us.1 The study could not identify a meaningful ventilatory contribution attributable to high-flow nasal cannula. While we applaud the authors’ methodology, we feel that the working methodology of high-flow nasal cannula needs to be considered in context with the conclusion and interpretation.
Variations in lung mechanics need to be considered when the interplay of high-flow nasal cannula oxygenation and carbon dioxide exchange are examined. Respiratory mechanics during high-flow nasal cannula oxygenation is likely to differ substantially between the paralyzed and unparalyzed states as in spontaneous and assisted or controlled breathing. The high-flow nasal cannula is believed to generate a level of pharyngeal pressure.2 Thus,...
