Fig. 2

Schematic of airway pressure dynamics in “anterograde tracheal catheterization” versus using an LMA. Status one is a schematic of the air dynamics with the LMA. In this condition, the leak site locates proximal to the resistance (stenosis). The leak is started and driven by \( {P}_B \)-\( {P}_a \) before a sufficient maximal \( {P}_A \) is achieved. This leak increases if greater pressures (\( {P}_B \)) are imposed by use of BVM ventilation. By using the “anterograde tracheal catheterization” as shown in the 2nd status, the leak site is transferred distal to the resistance (narrow catheter lumen in this condition). In this condition, the leak area is smaller and is a function of \( {P}_A \)-\( {P}_a \). Thus, any manually increased \( {P}_B \) cannot increase the leak unless it increases the \( {P}_A \). \( {P}_A \) alveolar pressure, \( {P}_a \) atmosphere pressure, \( {P}_B \) pressure within the bag