Clinical application of a curved video suspension laryngoscope in laryngeal surgery

Abstract

Background

Suspension laryngoscopy (SL) is a common procedure performed by otolaryngologists. Studies have shown that adverse effects occur often during SL.

Objectives

To demonstrate the value of clinical application, this study compared the surgical time and postoperative oropharyngeal complications of SL using a novel curved video suspension laryngoscope with those of conventional SL.

Materials and methods

A total of 185 patients who underwent curved video SL, and 128 who underwent conventional SL were included. Characteristics including age, sex, body mass index (BMI), postoperative complications, and surgical time were compared in conventional and curved SL patients diagnosed with vocal cord polyps.

Results

The use of a curved laryngoscope significantly reduced surgical time (median, 10 min IQR 7–15 vs. 15 min IQR 11–20; p < .001) and produced fewer postoperative complications (2 vs. 39, p < .001) than that of conventional SL. Patients undergoing conventional SL experienced an 18.8-fold higher complication risk vs. those undergoing curved video SL (adjusted OR = 18.80; 95% CI = 6.47–54.60).

Conclusions and significance

Curved video SL provided a clear surgical field, consumed less surgical time, and yielded fewer complications than conventional SL. This procedure is a cost-effective, minimally invasive alternative to conventional SL.

Chinese Abstract

背景：悬吊式喉镜检查 (SL) 是由耳鼻喉科医师进行的常见手术。研究表明, 在 SL 过程中经常发生不良影响。

目的：为了证明临床应用价值, 本研究比较了使用新型弯曲视频悬挂喉镜的SL手术与传统 SL 的手术时间和术后口咽并发症。

材料与方法：共纳入185例接受弯曲视频SL的患者, 128例接受传统SL的患者。比较常规和弯曲 SL 患者的年龄、性别、体重指数 (BMI)、术后并发症和手术时间等特征。这些患者被诊断患有声带息肉。

结果：与传统的 SL相比, 弯曲喉镜的使用明显缩短了手术时间（中位数, 10 分钟 IQR 7–15 相较于 15 分钟 IQR 11–20； p < .001) 并产生更少的术后并发症（2 相较于 39, p < .001)。接受传统 SL 的患者经历了比接受弯曲视频 SL 的患者高18.8 倍的并发症风险（调整后的 OR = 18.80；95% CI = 6.47–54.60)。

结论和意义：与传统的 SL相比, 弯曲视频SL可提供清晰的手术区域, 手术占时更少, 并且 产生的并发症更少。该手术是传统 SL 的一种具有成本效益的微创替代方案。

Keywords:

• Curved suspension laryngoscope
• clinical application
• complications
• surgical time

Introduction

Endolaryngeal microsurgery is usually accompanied by the use of suspension laryngoscopy (SL) to treat vocal cord lesions, including benign and malignant changes. The anatomy of the oral cavity and the pharynx is clearly curved, yet SL relies on a direct ‘line-of-sight’ of the glottis by aligning the oral, pharyngeal, and laryngeal axes [1,2]. This conventional approach could result in unnecessary injury or local trauma due to potential postoperative complications, including hypoesthesia, immobility of the tongue, laceration of the lateral tonsillar pillar, tooth fracture, swelling, mucosal injury, bleeding, incomplete surgery, and longer surgical time [3–6]. Elevating the head, pressing the throat, and using a flexible fiberscope are some of the currently used alternative approaches, each having certain advantages and disadvantages [7,8]. Optimal therapy requires new solutions to address shortcomings as far as possible.

Curved video SL is currently the most preferred solution. Inspired by the anesthetic laryngoscope, we utilized biomechanical numerical simulation to design a novel curved video SL laryngoscope that has received a patent certificate if applied to clinical practice. The curved video SL system has several advantages, including a labor-saving instrument, bimanual handling, and stereoscopic view in high-resolution magnification. In this study, we aimed to explore the clinical advantages of using the curved video SL system to resect vocal cord lesions during endolaryngeal surgery. Here, we describe the surgical procedure and demonstrate its clinical usefulness in a patient cohort.

Methods

This study was approved by the ethics committee of the Second Affiliated Hospital of Dalian Medical University, and informed consent was obtained from the patients undergoing surgery. A total of 313 patients who underwent endolaryngeal microsurgery for vocal cord polyps were included in this retrospective analysis. The patients were either treated using conventional SL or with a curved laryngoscope to assess surgical time and postoperative complications. Of the 313 patients enrolled in the study, 185 underwent curved video SL, and 128 patients underwent conventional SL. The surgeries were performed by the same surgeon between January 2016 and March 2021.

The curved video SL model was preliminarily designed and improved by the Materialise Interactive Medical Image Control System (MIMICS) (Materialise NV, Leuven, Belgium) method. ANSYS Workbench (ANSYS, Canonsburg, PA) finite element analysis and processing software was used for the numerical simulation. A threshold was set using MIMICS and ANSYS Workbench software to obtain a suitable bending radius and angle. When the results of the numerical model and the length of the SL device were combined, a tubular laryngoscope with a radius of 8 cm, corresponding angle of 120° (the angle between the line of the upper incisor to the tongue root and the line of the tongue root to the vocal cords), and an arc length of 17 cm was used (Figure 1(a)). The device was constructed in disposable medical plastic, which did not contain metals. A high-resolution, custom-made endoscope was placed laterally penetrating the laryngoscope (LBTK-CAMC-H, Dalian Labtek Science & Development Co., Ltd, Dalian, China). The laryngeal tube located on the side could also be combined with a fiber laryngoscope made by other manufacturers. A video camera system (LBTK-LCDC-H, Dalian Labtek Science & Development Co., Ltd, Dalian, China) was connected to the endoscope, and the endolaryngeal image was displayed on an LCD monitor (LBTK-LCDC-H, Dalian Labtek Science & Development Co., Ltd, Dalian, China) (Figure 1(b)). A series of instruments with a curvature similar to the curved laryngoscope were designed to perform the surgery (Figure 1(c)). In addition, a conventional instrument holder enabled fixation and bimanual handling of the flexible instruments (Figure 1(d)).

Figure 1. Curved laryngoscope customized with medical plastic materials (a). Curved video SL system connected to a video camera and LCD monitor (b). A set of curved instruments designed by us (c). Available instrument holder was connected with the anatomically shaped curved video laryngoscope (d).

General anesthesia with endotracheal intubation and muscle relaxers was administered prior to the endolaryngeal surgery. The curved laryngoscope was inserted through the uvula and retropharyngeal wall, exposing and allowing resection of the vocal cord polyps after adjusting the position of the head and neck and pressing down the thyroid cartilage. The surgeon guided the curved video laryngoscope through the uvula and retropharyngeal wall, elevating the epiglottis under the guidance of the side endoscope and fully exposing the vocal cord lesions. This procedure allowed for complete removal of the vocal cord polyps with a self-made arc laryngeal instrument. The curved laryngoscope allowed the surgeon to use an instrument holder to perform the surgery bimanually.

Major SL complications involve events requiring airway management; however, this study was designed to evaluate the incidence of oropharyngeal complications [9,10]. Swallowing discomfort; oral mucosa injuries, including the gums, lips (mucosa and skin), and tongue; and temporary lingual nerve injuries were all considered as postoperative complications in our study. The incidence of postoperative complications was calculated and analyzed with respect to age, sex, body mass index (BMI), and the two different suspension systems. The surgical time was also analyzed statistically.

Statistical analysis was performed using SPSS software version 23.0 (IBM, Armonk, NY). Student’s t-test, Mann–Whitney U test, Chi-square test, and Fisher’s exact test were used in the statistical analyses, where p < .001 was considered significant. A multivariate analysis was performed to determine the influence of confounding factors. All patients were followed-up for up to 1 month after surgery, wherein improvements of hoarseness were noted.

Results

The incidence of postoperative complications related to the two different SL procedures is shown in Table 1. No significant differences in age, sex, or BMI were observed among patients with and without postoperative complications. Compared with patients who underwent conventional SL, patients who underwent curved video SL exhibited significantly reduced complications. Only two complications were observed in patients undergoing curved video SL, whereas 39 were observed in patients undergoing conventional SL (Table 1; p < .001).

Table 1. Incidence of postoperative complications after different suspension laryngoscopy (SL).

Variable	SL (n = 128), n (％)	Curved video SL (n = 185), n (%)	p Value
Age ($\overline{X }$± s, years)	48.91 ± 11.131	47.19 ± 11.494	.189
Sex			.393
Male	56 (43.75)	90 (48.65)
Female	72 (56.25)	95 (51.35)
BMI (IQR, kg/m^2)	25 (22.80–27.88)	25 (22.90–27.75)	.821
Complications			<.001
Yes	39 (30.47)	2 (1.08)
No	89 (69.53)	183 (98.92)

BMI: body mass index; SL: suspension laryngoscope

p Values showing differences between the two suspension laryngoscopes.

Table 2 provides further details on the postoperative oropharyngeal complications. The association of complications with the specific suspension system was statistically significant (p value < .001; Table 2). Postoperative complications were mainly divided into three categories: swallowing discomfort, oral mucosal injuries, and temporary lingual nerve injuries. The most common complication associated with conventional SL was oropharyngeal mucosa injuries, including the gums (n = 3), mucosa (n = 26), and lips (n = 7). In one patient, swallowing discomfort was recorded. Only two lingual nerve injuries of the tongue occurred after conventional SL, and two oropharyngeal mucosa injuries occurred when curved video SL was performed (Table 2; p < .001).

Table 2. Oropharyngeal complications of conventional SL and curved video SL.

Complications	SL (n/128)	Curved video SL (n/185)	p Value
Swallowing discomfort	1/128	0/185	<.001
Oral mucosa injuries
The gums	3/128	0/185	<.001
Mucosa	26/128	2/185	<.001
Lips	7/128	0/185	<.001
Temporary lingual nerve injuries	2/128	0/185	<.001

SL: suspension laryngoscope

p Values showing differences between the two suspension laryngoscopes.

The difference in SL procedure duration between the two groups was statistically significant (Table 3; p < .001). The median surgical times were 15 and 10 min for conventional SL and curved video SL, respectively. Therefore, the duration of operative time for curved video SL was significantly shorter than that of conventional SL. Patients were followed-up 1-month post-surgery, and re-examination showed that patients who underwent either procedure (conventional SL or curved video SL) had no tumor residue or recurrence and no hoarseness.

Table 3. Comparison of surgical time of conventional SL and curved video SL.

	SL (IQR)	Curved video SL (IQR)	p Value
Surgical time/(min)	15.0 (11.00–20.00)	10.0 (7.00–15.00)	<.001

SL: suspension laryngoscope

p Values showing differences between the two suspension laryngoscopes.

Finally, Table 4 shows the results of the multivariate logistic regression analysis for the association between postoperative complications and age, sex, BMI and different suspension systems. Patients who underwent conventional SL had an 18.8-fold increased risk of complications compared with those who underwent curved video SL (adjusted OR = 18.80; 95% CI = 6.47–54.60).

Table 4. The results of multivariate logistic regression of each factor and postoperative complications.

Variable	B value	Standard error	p Value	Adjusted odds ratio (95% CI)
Age (years)	0.25	0.017	.144	1.03 (0.99–1.06)
Sex
Female	0.53	0.384	.167	1.70 (0.80–3.61)
Male^a
BMI (kg/m^2)	0.63	0.052	.222	1.07 (0.96–1.18)
Suspension system
SL	2.93	0.544	<.001	18.80 (6.47–54.60)
Curved video SL^a

BMI: body mass index; SL: suspension laryngoscope; CI: confidence interval

^aFor comparison.

Discussion

An ideal laryngoscope, which can be inserted safely, provides accurate anatomic exposure, has improved maneuverability, and is labor-saving, has not yet been widely applied in clinical surgery despite the advancements in laryngoscopy techniques and instrumentation over the last decades. This study confirmed that conventional SL inevitably exerts pressure on the oropharyngeal and laryngeal tissues, leading to a higher risk of lingual and glossopharyngeal nerve injuries than previously recognized [11].

In 2002, Müller et al. [12] reported a patient whose endolarynx could not be exposed to straight laryngoscopes. However, immediate improvement was observed when a curved laryngoscope at a 50° angle was used. Kim et al. [13] described a curved rigid laryngoscope accompanied by an imaging system that provided improved visualization and caused fewer traumas. Recently, Schild et al. [14] employed an ex vivo porcine laryngeal model to demonstrate that a curved prototype combined with large monitor visualization could provide a cost-effective, minimally invasive alternative. However, this approach has not yet been applied in clinical practice. Moreover, material, fixation, and pipe size limitations have been reported with curved laryngoscopes, including rigid curved laryngoscopes and video laryngoscopes [13–15].

Our device differs from the abovementioned curved laryngoscopes. An advantage of our design is that it simulated the oropharyngeal and laryngeal surgical situation, established the model, and provided relevant and reasonable design data, such as pipe size, angle, and material. Ultimately, we designed a curved laryngoscope with a radius of 8 cm, a corresponding angle of 120°, and an arc length of 17 cm. Using MIMICS and ANSYS to create the curved laryngoscope design; we analyzed the pressure on the tongue and incisor teeth, and obtained the major force point exerted by curved laryngoscopes of different sizes. The process of moving the curved laryngoscope into the pharyngeal airway was simulated until the front end of the curved laryngoscope reached the epiglottis; stress and deformation data were collected based on the overall model of the tongue tissue and incisors. Computer analysis showed that the size of the curved laryngoscope in this study provided less pressure on the tongue and incisors. Our results confirmed that the curved laryngoscope produced fewer complications than laryngoscopes used in conventional SL. Moreover, the curvature radius of the laryngoscope used in this study was applicable to all 185 patients who underwent curved video SL. However, it is possible that there are other existing limitations that we have not yet encountered. In future studies, we will adjust the parameters of the curved laryngoscope to address any unsuitable conditions, therefore, allowing generalizability of our findings.

Another important feature of our curved laryngoscope design is that we used medical plastic instead of steel to avoid excess pressure on the tongue muscle and pharyngeal tissues. Xidong et al. [16] discussed the disadvantages of conventional SL, emphasizing that it could potentially cause damage or injury to the physiological structures. When compared with laryngoscopes used in conventional SL, our curved laryngoscope significantly reduced physical distortion of the oropharyngeal tissues, caused negligible stimulation of the vagus nerve, produced no difference in the heart rate, and virtually improved the endolaryngeal exposure of all patients (especially obese patients with shorter necks), owing to the similarity of its shape to that of the lingual muscle tissue. Our results also showed a significant reduction in postoperative complications when using curved laryngoscopes vs. conventional laryngoscopes. In our study, oropharyngeal mucosal injuries due to conventional SL accounted for a higher overall complication rate (30.47%) than that previously reported in the literature. This finding might be related to the rigidity of materials used in the laryngoscopes and the spinal rigidity of the patients reported in previous studies. In addition, we investigated other factors that might be associated with the incidence of the complications, including age, sex, and BMI. None of these features were shown to be significantly associated with the incidence of complications; however, the type of suspension system was significantly related to such. Follow-up results showed that using the curved laryngoscope not only decreased the occurrence of complications vs. the laryngoscopes used in conventional SL, but also helped achieve satisfactory surgical outcomes equivalent to those of conventional SL.

In addition, the design of the curved video SL system significantly reduced the lifting force required to completely expose the glottis, which facilitated the complete removal of vocal cold lesions. Difficult laryngeal exposure is a challenging clinical situation and a leading cause of operation termination in phonomicrosurgery in conventional SL [17]. Our curved video SL design potentially overcomes this problem. Among 185 patients who underwent endolaryngeal surgery with curved video SL at our hospital during a 5-year period, the method provided complete accessibility and improved exposure of the glottis and anterior commissure. Representative endolaryngeal images are shown in Figure 2(a–c). Visualization and accessibility of laryngeal structures (vocal cords, vestibular folds, anterior commissure, and ventral subglottis) were easily obtained in all cases using the curved video SL system. Additionally, some patients with shorter necks, cervical spinal rigidity, obesity, and significant overbites were treated successfully with the curved laryngoscope.

Figure 2. Laryngeal exposure and a precise bimanual monitor-guided operation with curved video SL. The entire glottis was exposed including the anterior commissure. Preoperative image (a). Interoperative image (b). Postoperative image (c). Bimanual operation (d).

Tessema et al. highlighted the importance of limiting the suspension time [18], and concluded that longer surgeries incurred a higher risk of tongue-related complications. In our study, two of 39 patients had temporary lingual nerve injury after conventional SL. Notably, we were able to reduce the surgical time to an average of 10 min when using the curved video SL system. A reduction in surgical time may allow the use of lower amounts of general anesthetics, induction agents, and neuromuscular blocking drugs, thus enabling a shorter recovery time.

In our experience, the external video camera and LCD monitor employed in our system delivered an excellent view of the glottis and facilitated a precise monitor-guided operation. Using both hands during surgery provided stability, thereby enabling accurate resection of the lesions and effectively reducing the surgical time (Figure 2(d)). These features improved surgical efficiency and potentially, surgical outcomes.

However, some limitations of this method still exist, including the requirement for a specifically designed set of instruments with the same curvature as that of the curved laryngoscope. Another is that the instruments used in a curved tube are not as broadly applicable as we had hoped. Schild et al. [14] used a manually operated endoscopic tool, Di Lumen, to allow flexibility of surgical instruments. The flexible instrument could be tilted up to 90° (polar angle) and 360° (azimuthal angle). However, techniques requiring fine manipulation, such as the microflap technique, are difficult to perform using such a curved laryngoscope. In the future, finer and more flexible instruments should be designed.

In conclusion, this novel curved video SL system provided improved exposure of the supraglottis and glottis, and applied only limited force on the tongue muscles. Also, using the curved video SL system significantly reduced surgical time and produced fewer complications. Our novel adaptation of the curved video SL system in clinical practice preserves the advantages of traditional laryngoscopes and provides the ability to operate bimanually. This new technique not only offers an effective solution for phonomicrosurgery, but is also a cost-effective, minimally invasive alternative to conventional SL for future surgeries.

Acknowledgments

The manuscript has not been published before, and it is not under consideration for publication anywhere else.

Disclosure statement

No potential conflict of interest was reported by the author.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (NO.11772087). Patent: The patent has awarded by National IP Bureau (ZL 2014 2 0605538. 0).