Difficult airway is an eternal topic in anesthesiology. There are many methods and tools to deal with difficult airway, but the problem of difficult airway has not been completely solved.
At present, there are many kinds of endotracheal intubation assistant tools, the most used are video laryngoscope (bladed laryngoscope) and ordinary direct laryngoscope. In the treatment of difficult airway, the flexible fiberoptic bronchoscope is the classical and universally accepted choice. Optical stylets integrate flexible fiberoptic imaging features in a rigid intubating stylet. Not only can it be applied to normal airway intubation, but also shows the prospect of assisting difficult intubations. The SOS, one of the most used intubating fiberoptic stylets, has the unique advantages and characteristics. Firstly, it has a portable and reusable scope with a shapeable stainless-steel stylet and adjustable tube stop. Secondly, a special port allowed to delivery oxygen to the patient. Furthermore, the high resolution eyepiece with light source can be used independently, or connected with a camera or a monitor. It has been widely used in clinic because of its fast, effective and little effect on hemodynamics. 2,3
Ultrasound technology is more and more used in clinical anesthesia due to its safe, reliable, repeatable and easy to realize characteristics. In the case of endotracheal intubation, using ultrasound image, we can determine the endotracheal tube size,[5–7] observe the position of cricothyroid membrane and glottis,1,4,5,8 guide tracheal intubation,1,4,5 judge whether the tracheal tube enters the trachea,1,4,5,9 and judge whether the position of tracheal tube is correct.5,10−12 At present, portable ultrasound is the standard equipment in many hospitals, which is easy to get, and is very suitable for promotion and application in basic hospitals.
UGTI is still a relatively new method in China and aboard. As mentioned above, real-time surface UGTI and SOS-aided tracheal intubation are similar in their operational procedures and applicable patients. To our knowledge, there is no study comparing these two methods. The purpose of this study is to compare UGTI with SOS-aided tracheal intubation, to explore the feasibility and practicability of UGTI, and to provide reference for clinical airway management. As the results showed, both ultrasound and SOS were successfully applied to endotracheal intubation with comparable first-attempt success rate and time for tracheal intubation.
In this study, we selected the anesthetized adult patients with normal airways to perform UGTI. We found that the tracheal tube and stylet were not hyperechoic, but their characteristic hypoechoic shadow in the pharynx could be immediately identified and then guided into the trachea with ultrasonography. The characteristic of UGTI is to be guided by the external view of the airway rather than the internal visualization of the airway. What's more, the operator could evaluate the relationship between the tracheal tube tube with the glottic structures in the whole process of intubation. The visual information of ultrasound could assist to identify the location of the resistance either on the arytenoid cartilages or the vocal cords during advancing the styletted tube. Then, the operator could make some adjustments to bypass the resistance.1,4,5
There are some limitations of UGTI. Firstly, two anesthesiologists are required to complete UGTI, one of them to obtain ultrasound visualization and the other to intubate. Secondly, the poor ultrasound images might affect its application. Thirdly, it is necessary for the operator to have the basic knowledge of ultrasound machine in order to perform the typical controls and adjustments. Notably, it is essential to conduct clinical training in visualization of the airway structures and sonographic features of successful tracheal intubation using ultrasound before attempting UGTI.4 Fourthly, further evaluation is required to determine the optimal stylet structure, although the stylet has been bent to simulate the shape of airway from the central incisors to the cricoid cartilage. Fifthly, this technique has the potential for airway injury, although accurate the ultrasound image was necessary for correct intubation. Regardless of the intubation method, the anesthesiologist should stop inserting the tracheal tube once resistance appeared. Inappropriate strength might increase the risk of airway injury during the procedure of intubation. Finally, it is worth mentioning that experience and capability are critical to the successful of any techniques in clinical application. In terms of the possible bias in a randomized controlled trial, the operators must be able to be proficient in the techniques studied,13 even all of the tracheal intubation in this study were performed by a specified anesthesiologist who were skilled in using the ultrasound and SOS in tracheal intubation.