We appreciate the comments by Fishler and Laloë regarding our article.1Their remarks are important to evaluate the dimensions of the tracheobronchial tree. To choose the double-lumen tube (DLT) size, the diameter of the mainstem bronchus and the diameter of the trachea are important. Usually, the ratio of occipitofrontal diameter and transverse diameter is within 0.9 to 1.1. However, in some patients, its ratio is beyond this range. In such cases, measurement using three-dimensional reconstructed images would be ideal, but it would not always be available. In that case occipitofrontal diameter in computed tomographic images would be the next choice. Brodsky et al. 2reported that the width of the trachea and the width of the left mainstem bronchus were closely correlated. Considering this, selecting the DLT size by the diameter of the trachea would be the third choice.
In our article we discussed the availability of a right-sided DLT. From this point of view, the length rather than the diameter of the right mainstem bronchus was important. As compared with the diameter, the length of right mainstem bronchus could be accurately measured from an x-ray image. The ratio of magnification can be calculated by the width of the endotracheal tube on the x-ray image and real tube width. Thus, our method was adequate for our purpose.
In our routine practice, we carefully examine the computed tomographic image as well as the x-ray image, and then we decide the type and the size of DLT in each patient, considering the side and the type of operation. Careful preoperative image examination is essential for thoracic anesthesia.
Some anesthesiologists seemed to consider that fiberoptic bronchoscopy (FOB) was best for examining the adequacy of the DLT’s positioning. Of course, FOB is most useful in positioning the DLT; however, we thought that the adequacy of the DLT’s positioning should be confirmed by quality of ventilation. If we could adequately ventilate the lung (each lobe), the tube’s position should be considered to be adequate. Here we illustrate the most distal acceptable position (fig. 1A) and the most proximal acceptable position (fig. 1B) of the right-sided DLT as defined by Benumof et al. 4In figure 1A, the ventilation slot seemed to be blocked by the bronchial wall. However, when we selected an adequate size of DLT, namely the diameter of the bronchial tip was smaller than the diameter of the bronchus in some extent, air could flow from/to the right upper lobe through the space between the bronchial wall and the bronchial tip of DLT (indicated by the arrow). As a result, we could probably ventilate the right upper lobe through this space. Of course the modification of the bronchial tip by Bussières et al. 3could increase the visibility of the orifice of the right upper bronchus through FOB, which would have an advantage for anesthesiologists. But their modification would not alter the most distal acceptable position of the right-sided DLT. Similarly, it would not alter the most proximal acceptable position either. The positions are only determined by the length of the right mainstem bronchus and the length of the bronchial cuff, with the conventional concept of definition for positioning the DLT by Benumof et al. 4Finally, we stated that their modification seems to offer little improvement in positioning and applicability of a right-sided DLT.
We should also pay attention to the rotation of the tube position. In such cases, we sometimes found it difficult to exactly fit the ventilation slot to the orifice of the upper bronchus. However, in most cases we could maintain adequate oxygenation and ventilation beyond all expectations. Thus, exact matching of the ventilation slot to the orifice of the upper bronchus is not always required to obtain proper oxygenation and ventilation. If an exact match was required, we could not properly use the right-sided DLT in most cases.
The purposes of our modification of the bronchial tip and the cuff shape were to increase the applicability of a right-sided DLT for more patients, to increase the safety margin in positioning, and to increase usability. To archive these purposes, we proposed our new concept and devised the new tube. We believed that our design achieved our purpose.
*Osaka University Graduate School of Medicine, Suita City, Osaka, Japan. email@example.com