The Margin of Safety of a Left Double-Lumen Tracheobronchial Tube Depends on the Length of the Bronchial Cuff and Tip

The left tracheobronchial double-lumen tube is the commonest device to separate the left and right lungs for differential ventilation. With the appropriate tube, the left bronchial cuff is positioned in the bronchus so that the cuff is beyond the carina but the tip of the tube does not occlude the aperture of the left upper lobe bronchus. The difference between the length of the left main bronchus and the length of the cuff and tip of the bronchial segment of the tube has been termed "the margin of safety" by Benumof. If the length of the cuff plus the tip exceeds that of the left main bronchus, there will be occlusion of the left upper lobe bronchus. The bronchial cuff and bronchial tip lengths were measured on two hundred and twenty left tracheobronchial (double-lumen) tubes from four manufacturers. The largest cuff-tip length was 40 mm with a Portex 41Fr tube but some 41Fr tubes from all manufacturers had cuff-tip lengths of 33 mm or greater which exceed the length of the shortest left main bronchus measured by Benumof. There was also a marked variation in cuff-tip lengths of the same size tube from the same manufacturer. The largest variation was 18 mm for the Portex 41 but substantial variation of 8 mm or more was found in at least one French size of all manufacturers. Users must be aware that significant cuff-tip length variation occurs and match the selected tube to the patient to ensure an adequate margin of safety.