**1. Introduction**

Airway management has often presented challenges for clinicians since the early times when direct laryngoscope (DL) was invented [1, 2]. The complications related to difficult airway or failed tracheal intubation can be devastating to both the patients and the anesthesiologists. Clinicians have continually strived to improve tracheal intubation techniques and devices to avoid complications. In this article, we review the role of video-assisted intubating stylet (VS; also known as the Shikani optical stylet technique for intubation), and we focus on its technical aspects and its potential advantages over conventional DL and videolaryngoscope (VL).

The term "optical stylet" was coined by George Berci and Ronald Katz in 1979 [3, 4]. The main part of this device included a straight rigid endoscope functioning as an endotracheal tube stylet to facilitate endotracheal intubation. The straight design of the stylet was however not workable for cases of difficult laryngoscopy and the device had to be introduced with the aid of a Macintosh laryngoscope. The technique of tracheal intubation with the rigid stylets was later improved in 1983 by Pierre Bonfils with a device that was similar. Instead of a straight design, it employed a fixed curved distal tip at the angle of 40 degrees [5]. This allowed better access to the anteriorly located larynx. In 1996, Alan Shikani introduced the Shikani optical stylet (Clarus Medical, Minneapolis, MN, USA) and the first series were published in 1999 [6], with numerous large studies to follow. The Shikani stylet is semi-malleable and its tip may be bent to better fit to the patient's upper airway anatomy. With this newly designed stylet, Shikani also introduced a technique for tracheal intubation (the Shikani technique). Briefly, the operator grasps patient's mandible with one hand and lifts the jaw anteriorly and then introduces the optical stylet, preloaded with the endotracheal tube with the other hand and advances the combination into the larynx. Because the stylet "sees" where the endotracheal tube is going, successful entry into the trachea is confirmed by direct visualization, and importantly this is done without any need for using a Macintosh blade or putting any pressure on the teeth or extending the cervical spine. The Shikani technique for intubation is described in **Figures 1** and **2**.

**Figure 3** shows clinical endoscopic views confirming by endoscopy (**Figure 3A**), whereby VS provides clear glottic view before sliding the endotracheal tube (ET tube) into the trachea (**Figure 3B**). VS is superior to DL and VL in obtaining an easy look at the glottic area and ensuring smooth railroading of the ET tube into trachea. Although VL with different angles/shapes of the blades frequently provides a decent laryngeal and glottis view, the operator may sometimes encounter difficulty in sliding the ET tube into the glottis, with occasional laryngeal trauma or misguided esophageal intubation. This could be due to the inherent design of VL device, inadequate mouth opening and/or oropharyngeal space, three axes alignment, etc. [7–11]. These issues are easily circumvented with VS.

Our experience and that of many others has shown optical stylets to be simple, durable, portable and lightweight, easy to learn and handle, affordable, and convenient to clean and disinfect [12–15]. The Clarus Video System (Clarus Medical LLC, Minneapolis, MN, USA) is a modification of the Shikani optical stylet which was originally introduced in the mid 1990s and since then multiple similar video-assisted intubating stylets have also been brought to market (**Table 1**). At our institution, we are currently equipped with 22 sets of four different brands of VS for routine use on daily basis since 2009 (**Figure 4**). Ours is an 1110-bed tertiary medical center with 1788 personnel, 20 operation rooms, 18 attending anesthesiologists, and 54 nurse anesthetists. Out of all surgeries that needed general anesthesia and tracheal intubation, more than 90% of the intubations were performed using VS (**Table 2**). The rest of tracheal intubations were conducted using flexible fiberoptic endoscope (FOB) mostly in some selected predictable difficult airway scenarios. In contrast, VL was

#### **Figure 1.**

*The Shikani technique for intubation using the Shikani optical stylet. (A) Head is initially in the resting position. (B) Head is placed in the sniffing position, and the mandible is lifted with the left hand. (C) Stylet, preloaded with the endotracheal tube, is inserted into the mouth with the right hand, and the larynx is visualized. (D) Stylet– endotracheal tube unit is advanced through the vocal cords (arrow A) under direct visualization, and the stylet is removed (arrow B). (Courtesy of the SAGE Publishing. Permission to reproduce the images from [6] was granted).*

#### **Figure 2.**

*Demonstration of the Shikani technique for intubation using the Shikani optical stylet in cadavers. (A) Before insertion of VS. The oral space is occupied by the tongue. (B and C) Jaw-thrust by operator's left hand allows the insertion of VS into oropharyngeal space. The hockey stick design of the VS makes insertion easy to access the epiglottis and approach glottic area. (D) Entry of the VS into trachea.*

#### **Figure 3.**

*Laryngeal and glottic views. (A) A perfect full-range glottic view from a flexible esophagogastroduodenoscopy examination in a 66-year-old man when the patient was under procedural analgesia. (B) A view from the videoassisted intubating stylet (VS) in an 89-year-old woman during tracheal intubation and general anesthesia. Laryngoscopic definition: POGO scale 100%; Cormack-Lehane class: I.*




#### **Table 1.**

*Examples of commercially available video-assisted intubating stylet.*

#### **Figure 4.**

*Examples of commercial devices of VS. We apply the video-assisted intubating stylet technique at our institute on a daily routine basis. (A) C-MAC® VS, Karl Storz GmbH & Co. KG,Tuttlingen, Germany). (B) UE video stylet (UE, Xianju, Zhejiang, China). (C) Trachway video intubation system (Markstein Sichtec Medical Corp., Taichung,Taiwan). It is noted that these VS can accommodate various ET tubes, including regular ET tube (A), laser-resistant stainless steel ET tube (B), and double-lumen endobronchial tube (C).*


*GA: general anesthesia. LMA: laryngeal mask anesthesia. ET: endotracheal intubation. VL: videolaryngoscope. VS: videoassisted intubating stylet.*

#### **Table 2.**

*Use coverage of video-assisted intubating stylet technique for tracheal intubation in the Department of Anesthesia, Hualien Tzuchi Medical Center, Hualien, Taiwan from 2016 to 2021.*

used mostly for teaching purposes or personal preferences. With such a high volume of clinical practices using VS, we have acquired a significant experience with this technique and present it in the following sections.
