We aimed to identify the threshold for P0.1 in a breath-by-breath manner measured without airway occlusion for high respiratory drive. In this prospective observational study, we found P0.1 measured without airway occlusion, esophageal P0.1 and esophageal pressure swing had a positive correlation. However, the P0.1 threshold for high respiratory drive was calculated at approximately 1.0 cmH2O from the regression equation. Our calculations suggest a lower threshold of P0.1 measured without airway occlusion than that which has been previously reported.