To the Editor:—
Because of the interposition of the trachea between the esophagus and the great vessels, transesophageal echocardiography (TEE) visualization of the proximal aortic arch and innominate artery (INA) is usually fraught with difficulty.1–5After institutional research ethics board approval (West China Hospital, Sichuan University, Sichuan, PR China), we studied a new acoustic window for TEE imaging of large vessels anterior to the trachea by using a saline-filled endotracheal balloon during cardiopulmonary bypass (CPB). The methods are as follows.
The endotracheal balloon was made with the shaft of a No. 37 Univent® (Fuji Systems Corporation, Tokyo, Japan) blocker and part of a surgical glove. First, the blocker balloon of a Univent® blocker was removed, and the segment over the middle digit of a size 8 latex surgical glove was cut to a total length of 8 cm. The glove segment was attached to the distal part of the Univent® shaft using a No. 4 silk suture. The balloon was made to possess a diameter of 1.8 cm and a length of 6 cm while fully inflated.
In cardiac surgery patients, general anesthesia was induced with intravenous midazolam, muscle relaxant, fentanyl, and propofol. The endotracheal tube was initially inserted into either the left or the right main stem bronchus as evident by unilateral air entry with auscultation. The endotracheal tube was subsequently withdrawn until breath sounds were first heard over both lungs. At this point, the tip of the tube was considered to be located immediately proximal to the carina. The depth of the endotracheal tube between the teeth was recorded. The endotracheal tube was withdrawn 3–4 cm from the carina and fixated using tape. This recorded depth of the endotracheal tube with the tip at the carina would be used for positioning of the endotracheal tube after the initiation of CPB.
Transesophageal echocardiography was performed after anesthesia induction with a 4- to 7-MHz phased array probe (model 21396A; Hewlett-Packard, Andover, MA) and an ultrasound system (Hewlett-Packard Sonos 4500). Before tracheal intubation, the endotracheal balloon was passed through the endotracheal tube until the balloon tip was located exactly at the endotracheal tube tip. A mark was made on the balloon shaft for identification. After initiation of CPB, the endotracheal tube was withdrawn so that its tip was located 6 cm above carina as previously described. The balloon was inserted 6 cm beyond the above-noted marking on the balloon shaft. At this point, the distal end of the balloon was considered to be located immediately above the carina. The process of filling the balloon was monitored by TEE, and saline was injected until the outline of trachea was seen or the balloon pressure reached 30 mmHg.
The transverse view of the trachea with the saline filled balloon was detected as a round echo-free space that was located at the tip of the fan-shaped view. When the probe was placed at a depth of approximately 18–25 cm from the incisor, the sausage-shaped aortic arch, with its proximal part anterior to the trachea, was viewed at a multiplane angle of 0°. Using the upper esophageal (UE) aortic arch long axis, the TEE probe was adjusted until the image with the maximal major diameter was obtained. Figure 1is a sample image of UE aortic arch long axis with and without the endotracheal balloon.
To image the INA, using the UE aortic arch long axis, the probe was withdrawn gradually while visualization of the endotracheal balloon was maintained. As the aortic arch disappeared from the view, the transverse view of the INA was seen anterior to the trachea at multiplane angle of approximately 40° (20°–65°). The TEE probe was adjusted until the transverse INA image, which was most circular in form at 2 cm above the aortic arch, was obtained. This plane was named UE innominate short axis. The UE innominate long axis was detected at a multiplane angle of approximately 130° (110°–160°). In this view, the INA was seen to be arising from and connected directly to the proximal aortic arch. Figure 2is a sample image of UE innominate short axis with and without the endotracheal balloon.
The main reason for the “blind zone” in TEE is the tracheal air column, which lies right and ventral to the esophagus. Echo waves are scattered completely by air. In patients undergoing cardiovascular surgery involving CPB, ventilation is terminated, and endotracheal balloon insertion is feasible. The insertion of a saline-filled endotracheal balloon eliminates the tracheal air column, thereby making possible the TEE imaging of the proximal aortic arch and INA anterior to the trachea. This new acoustic window is named “TEE transtracheal acoustic window.”
This TEE transtracheal acoustic window seems to provide improved visualization of the proximal aortic arch and INA. The major limitation of this window is that it can only be used when the ventilator is disconnected or during CPB. Before and after CPB, routine TEE must be used. Further studies are required to compare quantitatively the image quality of the proximal aorta and INA, with and without the presence of an endotracheal saline-filled balloon.
*West China Hospital, Sichuan University, Sichuan, PR China. firstname.lastname@example.org