Glottis Simulator

To the Editor:

The complexity of endotracheal intubation is often mentioned in the literature ^[1-3]. Moreover, the Carlens double-lumen tube ^[4] is troublesome to passes beyond the glottis during intubation because of carinal hook. At this stage, the tube is rotated so as not to damage the vocal cords. Although superior polyvinyl chloride tubes are available, the "hooked tubes" are still used.

"After the patient is anesthetized and paralyzed, the doublelumen tube is inserted into the trachea using a rigid laryngoscope. The tube is held such that the tip of the bronchial lumen faces anteriorly… With the Carlens-left sided-or White-right sided-tubes, as the tip of the bronchial lumen passes the vocal cords, the tube is rotated 180[degree sign] to bring the carinal hook passes anteriorly to negotiate the vocal cords. After the carinal hook passes beyond the vocal cords, the Carlens tube is rotated 90[degree sign] to the right, whereas the White tube is rotated 90[degree sign] to the left, in order to have the bronchial lumen face the intended bronchus. Once the double-lumen tube is placed in the trachea, the tracheal cuff is inflated. Mechanical ventilation is then begun with tidal volume of 10 ml/kg and a rate of 8 breaths/min. The bronchofiberscope is then used to evaluate the bronchial tree and the position of the double-lumen tube ^[5]."

Unfortunately, there is no simulator to teach such maneuvers by using three-dimensional visualization. To decrease such difficulties, a glottis simulator was developed to help in the training of tube rotation maneuvers.

A disposable plastic coffee cup (50 mL) was used to make the simulator. At the base of plastic cup, on the external side, three cuts and two indentures were made with the sharp point of a disposable 30 x 1.5-mm needle. Two of the cuts are straight and symmetrical: x - x[prime], x[double prime] - x[triple prime]; the other cut is semicircular y - y[prime], as shown in Figure 1A.

Figure 1: Schematic design of the different phases of the construction of the glottis simulator. A, View of the base of the plastic cup with cuts x - x[prime], x[double prime] - x[triple prime] and y - y[prime]. B, View of the bottom of the plastic cup with the indentures (scored lines) z - z[prime] and z[double prime] - z[triple prime]. C, Lateral view of the plastic cup. The arrow indicates the folding maneuver of the "epiglottis." D, Lateral view of the plastic cup with the final positioning of the "epiglottis." E, Upper view of the plastic cup with the maneuvers to make the "vocal cords" malleable. F, Upper view of the plastic cup with the final form of the glottis simulator. e = "epiglottis" and vc = vocal cord.

The two straight indentures (scored lines), z - z[prime] and z[double prime] - z[triple prime], are also symmetrical, as indicated in Figure 1B.

(Figure 1C, Figure 1D, and Figure 1E) shows the folding maneuvers to simulate the anatomical structures, as follows. Figure 1C shows the "epiglottis," located in the central part of the bottom of the cup and delimited by the three cuts x - x[prime], x[double prime] - x[triple prime] and y - y[prime]. The "epiglottis" must be pressed and inverted toward the interior of the plastic cup, folding in to the level of its vertex, as indicated by the curved arrow. Figure 1D illustrates how the "epiglottis" must be positioned. The lateral delimitation of the two "vocal cords" are established by the respective indentures (scored lines) z - z[prime] and z[double prime] - z[triple prime]. These must be folded at the level of the indentures, flexed several times to become pliable, and bent toward the outside of the cup, as demonstrated in Figure 1E. The plastic cup must be internally greased with lidocaine spray to facilitate the sliding over its surface.

Roberto de Menezes Lyra, MSc

IAMSPE Servico de Cirurgia Toracica; 04049-901 Sao Paulo, Brazil