Figure 49-22 Schematic diagram showing the air bubble detection method for checking adequacy of the seal of the left endobronchial cuff of a left-sided double-lumen tube. A, When the left lung is selectively ventilated or exposed to any desired distending pressure and the left cuff is adequately sealed, no air will escape around the left cuff and out the open right suction port, and thus no bubbles will be observed passing through the beaker of water. B, When the left lung is ventilated or exposed to any desired distending pressure and the left endobronchial cuff is not adequately sealed, air will escape around the left cuff and out the open right suction port, and thus air bubbles will be observed passing through the beaker of water. (From Benumof JL: Anesthesia for Thoracic Surgery. Philadelphia, WB Saunders, 1987.)