A flow-leak correction algorithm for pneumotachographic work-of-breathing measurement during high-flow nasal cannula oxygen therapy
Measuring work of breathing (WOB) is an intricate task during high-flow nasal cannula (HFNC) ther-
apy because the continuous unidirectional flow toward the patient makes pneumotachography technically
difficult to use. We implemented a new method for measuring WOB based on a differential pneumota-
chography (DP) system, equipped with one pneumotachograph inserted in the HFNC circuit and another
connected to a monitoring facemask, combined with a leak correction algorithm (LCA) that corrects flow
measurement errors arising from leakage around the monitoring facemask. To test this system, we used
a mechanical lung model that provided data to compare LCA-corrected respiratory flow, volume and time
values with effective values obtained with a third pneumotachograph used instead of the LCA to measure
mask flow leaks directly. Effective and corrected volume and time data showed high agreement (Bland–
Altman plots) even at the highest leak. Studies on two healthy adult volunteers confirmed that corrected
respiratory flow combined with esophageal pressure measurements can accurately determine WOB (rel-
ative error < 1%). We conclude that during HFNC therapy, a DP system combined with a facemask and an
algorithm that corrects errors due to flow leakages allows pneumotachography to measure reliably the
respiratory flow and volume data needed for calculating WOB.