To the Editor:-We read with great interest the recent letters to the editor [1,2]relating to the conversion of a nasal intubation to an orotracheal intubation by Dr. Cooper. The letters certainly reiterated the safety and effectiveness issues of various tube exchange techniques, especially in patients with a difficult airway.
In the past few years in our institution, we have been using the WuScope (Achi Corp., Fremont, CA, and Asahi Optical Co.-Pentax, Tokyo, Japan) in the operating room to facilitate double lumen tube placements and to perform subsequent tube exchanges from a double lumen tube to a regular endotracheal tube (ETT) in patients with a difficult airway. One such case has been reported electronically in the May 1997 WuScope Newsletter, which can be accessed on the World Wide Web (http://www.achi.com/htm/newspg2.htm). The same technique has also been applied in the intensive care unit for numerous cases of tube exchange, including a case of conversion of a nasal intubation to an orotracheal intubation.
Briefly, our patient, having documented history of difficult intubation, was a morbidly obese man with a very limited head extension in the intensive care unit with acute pancreatitis, sepsis, and adult respiratory distress syndrome. He was being ventilated with 100% oxygen and maintaining a saturation of 85%. The task was to replace the 6.5-mm nasal ETT with a 8.5-mm oral tube. After the upper airway was topically anesthetized and the intravenous sedation was administered, the WuScope, preloaded with the new ETT, was inserted into the oropharynx and positioned anterior to the nasal ETT. As the blade entered the vallecula, the triangular opening between the anterior commissure of the vocal cords and the nasal ETT was easily exposed. A suction catheter (18 French) was advanced out of the new ETT lumen and passed through this triangular opening into the trachea. With the suction catheter securely held in place by the operator firmly compressing the new ETT at its proximal end, the nasal ETT was removed. The new ETT was then advanced over the suction catheter into the trachea. The entire tube exchange procedure was performed by one person, took only a few minutes, and the actual conversion time was less than 10 s, with no change in oxygen saturation.
The WuScope is a tubular laryngoscope with fiberoptic imaging. The rigid blade allows exposure of the larynx. The tubular structure overcomes soft tissue obstruction, creates an intubating space, and protects fiberoptic lenses from secretions. Most importantly, there is minimal interruption of the patient's ventilatory support, and the operator can visually ensure the new ETT a free passage through the glottis. The WuScope technique for tube exchange has worked well for us and should be considered by others as an alternative approach to this important and difficult problem.
Lastly, we would like to share with the readers some issues of importance. First, as with any of the previously reported tube exchange methods, [1-3,5,6]previous expertise with the use of the WuScope is essential. In our institution, we have a combined experience of more than 1000 intubations with this device. Second, we find the use of muscle relaxants is often not necessary for tube exchange using the WuScope technique because glottic exposure can be achieved in the neutral position without jaw lifting or head extension. Before the procedure, we first thoroughly suction the patient's upper airway, then trickle 10 ml lidocaine, 2 or 4%, into the pharynx to allow the glottic area to be anesthetized. Third, as with other techniques, care must be taken to ensure that the suction catheter is not inadvertently withdrawn as the original ETT is removed. Fourth, if one is concerned that the oxygen insufflation provided through the WuScope oxygen channel may be insufficient for a patient with severe adult respiratory distress syndrome, a tube exchanger, rather than a suction catheter, may be an alternative conduit for tube advancement and may provide the opportunity for jet ventilation if oxygen desaturation occurs or if the tube exchange requires additional time. 
Scott R. Andrews, M.D.
Susan D. Norcross, M.D.
Monique F. Mabey, M.D.
Chief Anesthesiologist; Department of Anesthesia
Joshua B. Siegel, M.D.
Staff Anesthesiologist; Department of Anesthesia and Critical Care; Kaiser Permanente Medical Center; Hayward, California
(Accepted for publication November 9, 1998.)