Accuracy of neck circumference in the diagnosis of overweight in children.

OBJECTIVE: The objective of this study was to estimate the accuracy of measuring neck circumference as a diagnostic method for overweight in 10-year-old children. METHODS: A cross-sectional diagnostic accuracy study was performed in 2019. The population was composed of 942 school children from the municipality of Palhoça, SC, Brazil. For each measurement of the neck circumference, sensitivity, specificity, positive and negative predictive values, likelihood ratio for a positive test, and accuracy were estimated using the receiver operator characteristic curve, with body mass index as a reference. RESULTS: The estimated overall accuracy was 88.9%. For males, the accuracy was 90.1%, and for females, 88.5%. A 30.0 cm neck circumference had a sensitivity of 22.8%, a specificity of 95.4%, a positive predictive value of 76.6%, a negative predictive value of 65.3%, a likelihood ratio for a positive test of 5.0, and an accuracy of 66.7% for all students. CONCLUSION: Neck circumference showed a global accuracy of 88.9% as a method for diagnosing overweight in 10-year-old children. Predictive values showed high values, mainly starting with a neck circumference of 30 cm.

Evaluation of neck ultrasound measurements as a difficult airway predictor: A prospective observational study.

This study aimed to investigate the relationship between cervical measurements and difficult airways using ultrasonographic measurements. American Society of Anesthesiologists grade I to III, male or female, 120 adult patients, undergoing elective surgery were enrolled in the study. The study involved measuring the distance of the trachea, cricoid cartilage, thyroid cartilage, vocal cord anterior commissure, and hyoid bone to the skin using a 10 to 13 MHz linear ultrasound probe in the transverse plane. Additionally, the length of the cricothyroid and thyrohyoid membranes, along with their distance from the skin, were measured using the probe in the sagittal plane. Subsequently, another experienced anesthesiologist conducted mask ventilation and intubation after the patient's induction of general anesthesia. Throughout this process, the patient was assessed for difficulties in mask ventilation, laryngoscopy, and intubation. 28 (23.3%) patients had a difficult airway. Analyzing the measurements associated with difficult airways, the most reliable predictor was the epiglottis midline-skin distance [AUC (area under the curve): 0.847, P < .001, cutoff: >19.9, sensitivity: 78.6%, specificity: 79.4%]. Additionally, other factors such as hyoid bone to skin distance, thyroid cartilage to skin distance, thyrohyoid membrane to skin distance, and vocal cord anterior commissure-skin distance were also identified as predictors for a difficult airway. The increase in the distance of the epiglottis midline, vocal cord anterior commissure, hyoid bone, thyrohyoid membrane, and thyroid cartilage to the skin at the level of the isthmus measured by ultrasonography is predictive of difficult airways. Based on our study outcomes, we assert that ultrasonographic evaluation can be used in the prediction of difficult airways.

Ultrasound Evaluation of Anterior Neck Soft-Tissue Thickness to Predict Difficult Intubation in Overweight Adult Patients Posted for Surgery under General Endotracheal Anesthesia - An Observational Study.

BACKGROUND: Ultrasonographic imaging has been recently become simple portable and non-invasive adjuvant for bedside assessment of anterior neck soft tissue thickness which when measured at different levels showed to have significant role in predicting difficult laryngoscopy. AIMS AND OBJECTIVES: Primary objective was Ultrasonographic measurement of anterior neck soft tissue thickness at 3 levels -Distance from skin to hyoid bone (DSHB) -Distance from skin to thyrohyoid membrane (DSTM) -Distance from skin to anterior commissure of vocal cord(DSAC) and to compare and correlate the findings with Cooks modification of Cormack-Lehane score in predicting difficult laryngoscopy. Secondary objective was to compare and correlate the ultrasonographic measurements with conventional airway assessment methods. MATERIALS AND METHODS: After obtaining approval from the ethical committee, 90 Patients with BMI above 25 kg /m2 was enrolled for the study. A day before the surgery a thorough Preanaesthetic evaluation and assessment of the airway is done using conventional methods. Then on the day of surgery ultrasonographic measurement of anterior neck at 3 levels was done and after inducing the patients laryngoscopy was done and Cooks modification of Cormack-Lehane score assessed. RESULTS: The optimal cut off values to predict difficult laryngoscopy was 1.26, 2 and 1.2 cms for DSHB, DSTM and DSAC respectively, and among the three skin to anterior commissure of vocal cord was observed to be best USG parameter with more area under the ROC curve. CONCLUSION: USG measurement of anterior neck soft tissue thickness can be useful in predicting difficult laryngoscopy in overweight and obese patients also it had more diagnostic accuracy than conventional methods like MMS in predicting difficult laryngoscopy.

RésuméArrière-plan L'imagerie échographique est récemment devenue un simple adjuvant portable et non invasif pour l'évaluation au lit du patient de l'épaisseur des tissus mous du cou antérieur qui, lorsqu'elle est mesurée à différents niveaux, s'est avérée avoir un rôle important dans la prédiction d'une laryngoscopie difficile. Buts et objectifs L'objectif principal était la mesure échographique de l'épaisseur des tissus mous du cou antérieur à 3 niveaux -Distance de la peau à l'os hyoïde (DSHB) -Distance de la peau à la membrane thyrohyoïdienne (DSTM) -Distance de la peau à la commissure antérieure de la corde vocale (DSAC) et pour comparer et corréler les résultats avec la modification de Cooks du score de Cormack-Lehane pour prédire une laryngoscopie difficile. L'objectif secondaire était de comparer et de corréler les mesures échographiques avec les méthodes conventionnelles d'évaluation des voies respiratoires Matériels et méthodes Après avoir obtenu l'approbation du comité d'éthique, 90 patients présentant un IMC supérieur à 25 kg/m2 ont été inclus dans l'étude. Un jour avant la chirurgie, une évaluation préanesthésique approfondie et une évaluation des voies respiratoires sont effectuées à l'aide de méthodes conventionnelles. Ensuite, le jour de la chirurgie, une mesure échographique de la partie antérieure du cou à 3 niveaux a été effectuée et après l'induction des patients, une laryngoscopie a été effectuée et la modification de Cooks du score de Cormack-Lehane a été évaluée. Résultats Les valeurs seuil optimales pour prédire une laryngoscopie difficile étaient respectivement de 1,26, 2 et 1,2 cm pour DSHB, DSTM et DSAC, et parmi les trois paramètres de la peau à la commissure antérieure de la corde vocale, il a été observé que le meilleur paramètre USG avec plus de surface sous la courbe ROC Conclusion La mesure par USG de l'épaisseur des tissus mous du cou antérieur peut être utile pour prédire une laryngoscopie difficile chez les patients en surpoids et obèses. Elle a également une plus grande précision diagnostique que les méthodes conventionnelles comme le MMS pour prédire une laryngoscopie difficile.

Anatomical Insights on the Cervical Nerve for Contemporary Face and Neck Lifting: A Cadaveric Study.

BACKGROUND: Despite the significant roles it plays in the functions of the platysma and lower lip, the cervical branch of the facial nerve is often overlooked compared to other branches, but its consideration is critical for ensuring the safety of neck surgeries. OBJECTIVES: The aim of this study was to clarify the anatomical discrepancies associated with the cervical branch of the facial nerve to enhance surgical safety. METHODS: The study utilized 20 fresh-frozen hemiheads. A 2-stage surgical procedure was employed, beginning with an initial deep-plane facelift including extensive neck dissection, followed by a superficial parotidectomy on fresh-frozen cadavers. This approach allowed for a thorough exploration and mapping of the cervical nerve in relation to its surrounding anatomical structures. RESULTS: Upon exiting the parotid gland, the cervical nerve consistently traveled beneath the investing layer of the deep cervical fascia for a brief distance, traversing the deep fascia to travel within the areolar connective tissue before terminating anteriorly in the platysma muscle. A single branch was observed in 2 cases, while 2 branches were noted in 18 cases. CONCLUSIONS: The cervical nerve's relatively deeper position below the mandible's angle facilitates a safer subplatysmal dissection via a lateral approach for the release of the cervical retaining ligaments. Due to the absence of a protective barrier, the nerve is more susceptible to injuries from direct trauma or thermal damage caused by electrocautery, especially during median approaches.

The Late Cretaceous eutherian Zalambdalestes reveals unique axis and complex evolution of the mammalian neck.

The typical mammalian neck consisting of seven cervical vertebrae (C1-C7) was established by the Late Permian in the cynodont forerunners of modern mammals. This structure is precisely adapted to facilitate movements of the head during feeding, locomotion, predator evasion, and social interactions. Eutheria, the clade including crown placentals, has a fossil record extending back more than 125 million years revealing significant morphological diversification in the Mesozoic. Yet very little is known concerning the early evolution of eutherian cervical morphology and its functional adaptations. A specimen of Zalambdalestes lechei from the Late Cretaceous of Mongolia boasts exceptional preservation of an almost complete series of cervical vertebrae (C2-C7) revealing a highly modified axis (C2). The significance of this cervical morphology is explored utilizing an integrated approach combining comparative anatomical examination across mammals, muscle reconstruction, geometric morphometrics and virtual range of motion analysis. We compared the shape of the axis in Zalambdalestes to a dataset of 88 mammalian species (monotremes, marsupials, and placentals) using three-dimensional landmark analysis. The results indicate that the unique axis morphology of Zalambdalestes has no close analog among living mammals. Virtual range of motion analysis of the neck strongly implies Zalambdalestes was capable of exerting very forceful head movements and had a high degree of ventral flexion for an animal its size. These findings reveal unexpected complexity in the early evolution of the eutherian cervical morphology and suggest a feeding behavior similar to insectivores specialized in vermivory and defensive behaviors in Zalambdalestes akin to modern spiniferous mammals.

Anatomical variations in the course of spinal accessory nerve in the neck triangles: A descriptive study.

BACKGROUND: Spinal Accessory Nerve (SAN), which innervates the sternocleidomastoid (SCM) and trapezius muscles, is closely related to the internal jugular vein (IJV) in the anterior triangle of the neck and passes superficially in the posterior triangle. Injury to SAN is a major complication of level II neck dissection, leading to shoulder syndrome. The present study aims to assess the course and its relation to the SCM muscle and IJV in the Tamil ethnolinguistic groups in South India. METHODS AND MATERIALS: The anterior and posterior triangles of the neck were dissected in 28 formalin-fixed adult cadavers. The course of the SAN and the entry and exit points of SAN along the SCM muscle were assessed using the mastoid process as the reference. Recorded data was analyzed using SPSS software. RESULTS: The SAN was anteriorly related to the IJV in 58.73%, posteriorly in 37.5%, and pierced through the IJV in 3.57% of the specimens. The entry and exit points of SAN from the mastoid process were 37.86±7.26mm and 48.55±8.22mm, respectively. In 86.67% of the cases, the SAN traversed through the SCM muscle, and in 13.33%, it was deep to the SCM. CONCLUSION: The present study reports that the SAN is variable in its course, and relation to SCM and IJV. Knowledge about the variant anatomy of the SAN in the triangles of the neck is important and it aids surgeons to prevent iatrogenic injuries to SAN or IJV and enhance surgical safety in neck procedures.

Magnetic resonance imaging-based classification of the myodural bridge complex and its influencing factors.

Cerebrospinal fluid (CSF) circulation is considered the third circulation of the human body. Recently, some scholars have proposed the myodural bridge (MDB) as a novel power source for CSF flow. Moreover, the suboccipital muscles can exert a driving force on the CSF via the MDB. This hypothesis is directly supported by head rotation and nodding movements, which can affect CSF circulation. The MDB has been validated as a normal structure in humans and mammals. In addition, the fusion of MDB fibers of different origins that act in concert with each other forms the MDB complex (MDBC). The MDBC may be associated with several CSF disorder-related neurological disorders in clinical practice. Therefore, the morphology of the MDBC and its influencing factors must be determined. In this study, T2-weighted imaging sagittal images of the cervical region were analyzed retrospectively in 1085 patients, and magnetic resonance imaging (MRI) typing of the MDBC was performed according to the imaging features of the MDBC in the posterior atlanto-occipital interspace (PAOiS) and posterior atlanto-axial interspace (PAAiS). The effects of age and age-related degenerative changes in the cervical spine on MRI staging of the MDBC were also determined. The results revealed four MRI types of the MDBC: type A (no MDBC hyposignal shadow connected to the dura mater in either the PAOiS or PAAiS), type B (MDBC hyposignal shadow connected to the dura mater in the PAOiS only), type C (MDBC hyposignal shadow connected to the dura mater in the PAAiS only), and type D (MDBC hyposignal shadow connected to the dura mater in both the PAOiS and PAAiS). The influencing factors for the MDBC typing were age (group), degree of intervertebral space stenosis, dorsal osteophytosis, and degenerative changes in the cervical spine (P < 0.05). With increasing age (10-year interval), the incidence of type B MDBC markedly decreased, whereas that of type A MDBC increased considerably. With the deepening of the degree of intervertebral space stenosis, the incidence of type C MDBC increased significantly, whereas that of type A MDBC decreased. In the presence of dorsal osteophytosis, the incidence of type C and D MDBCs significantly decreased, whereas that of type A increased. In the presence of protrusion of the intervertebral disc, the incidence of type B, C, and D MDBCs increased markedly, whereas that of type A MDBC decreased considerably, with cervical degenerative changes combined with spinal canal stenosis. Moreover, the incidence of both type C and D MDBCs increased, whereas that of type A MDBC decreased. Based on the MRI signal characteristics of the dural side of the MDBC, four types of the MDBC were identified. MDBC typing varies dynamically according to population distribution, depending on age and cervical degeneration (degree of intervertebral space stenosis, vertebral dorsal osteophytosis formation, simple protrusion of intervertebral disc, and cervical degeneration changes combined with spinal canal stenosis, except for the degree of protrusion of the intervertebral disc and the degree of spinal canal stenosis); however, it is not influenced by sex.

Imaging of the Craniocervical Junction: A Pictorial Review.

The craniocervical junction (CCJ) is a complex anatomical structure comprising the occiput, the atlas, and the axis. The CCJ plays an important role in maintaining stability, providing protection, and supporting neurovascular structures. The CCJ can be affected by a wide range of congenital variants and traumatic, degenerative, inflammatory, and tumoral pathologies. This pictorial review the normal anatomy of the CCJ and presents the most common anatomical variants and pathologic conditions affecting the CCJ.

An anatomical study of the suboccipital cavernous sinus and its relationship with the myodural bridge complex.

The suboccipital cavernous sinus (SCS) and the myodural bridge complex (MDBC) are both located in the suboccipital region. The SCS is regarded as a route for venous intracranial outflow and is often encountered during surgery. The MDBC consists of the suboccipital muscles, nuchal ligament, and myodural bridge and could be a power source for cerebrospinal fluid circulation. Intracranial pressure depends on intracranial blood volume and the cerebrospinal fluid. Since the SCS and MDBC have similar anatomical locations and functions, the aim of the present study was to reveal the relationships between them and the detailed anatomical characteristics of the SCS. The study involved gross dissection, histological staining, P45 plastination, and three-dimensional visualization techniques. The SCS consists of many small venous sinuses enclosed within a thin fibrous membrane that is strengthened by a fibrous arch closing the vertebral artery groove. The venous vessels are more abundant in the lateral and medial portions of the SCS than the middle portion. The middle and medial portions of the SCS are covered by the MDBC. Type I collagen fibers arranged in parallel and originating from the MDBC terminate on the SCS either directly or indirectly via the fibrous arch. The morphological features of SCS revealed in this research could serve as an anatomical basis for upper neck surgical procedures. There are parallel arrangements of type I collagen fibers between the MDBC and the SCS. The MDBC could change the blood volume in the SCS by pulling its wall during the head movement.

Appropriate neck circumference and waist-to-height ratio cut-off points as predictors of obesity and cardiovascular risk in adolescents.

OBJECTIVE: To determine neck circumference (NC) and waist-to-height ratio (WHtR) cut-off points as predictors of obesity and cardiovascular risk in adolescents. METHODS: Cross-sectional study developed with a subsample of 634 adolescents aged 18 and 19 years belonging to the third phase of the "RPS" cohort (Ribeirão Preto, Pelotas and São Luís) carried out in 2016. The area under the ROC curve (AUC) was identified to assess the predictive capacity of NC and WHtR in relation to the percentage of body fat (%BF), obtained by air displacement plethysmography (ADP), and the cardiovascular risk estimated by the Pathobiological Determinants of Atherosclerosis in Youth (PDAY). RESULTS: The prevalence of obesity by %BF was 7.6% in males and 39.4% in females (p-value <0.001), and the high PDAY risk was 13.8% and 10.9%, respectively. For males, NC cut-off point was 44.0 cm and the AUCs were 0.70 (95%CI 0.58-0.83) to predict obesity and 0.71 (95%CI 0.62-0.80) to predict high cardiovascular risk; for females, NC cut-off point was 40 cm and the AUCs were 0.75 (95%CI 0.69-0.80) and 0.63 (95%CI 0.53-0.73), respectively. WHtR cut-off point was 0.50 for both sexes; for males, the AUCs to predict obesity and high risk according to PDAY were 0.90 (95%CI 0.80-0.99) and 0.73 (95%CI 0.63-0.82), respectively; for females, they were 0.87 (95%CI 0.83-0.90) and 0.55 (95%CI 0.45-0.65), respectively. CONCLUSION: WHtR and NC are good discriminators to assess obesity and cardiovascular risk in adolescents, especially in males.

Quantifying research on anatomical structures, a potential new metric for assessing clinical relevance.

Human anatomy remains an integral part of medical education, and recent studies have documented an emerging consensus on the key anatomical learning objectives for physicians and other health professionals in training, both at the graduate and postgraduate levels. Despite this progress, less attention has been given to assessing the clinical relevance of individual anatomical structures, and which structures students should master to achieve these learning objectives. In this study we hypothesized that published research involving individual anatomical structures is largely driven by the clinical relevance of these structures, and that tabulating the number of such publications can provide an up-to-date, evolving metric of clinical relevance. To test this hypothesis, we developed a semi-automated search routine that uses the PubMed database to quantify the publication frequency of anatomical structures and compared that to a previous study that assessed the importance of structures of the head and neck using the Delphi method, a formal procedure of generating expert consensus. Using our new approach, we were able to rank the research intensity of 2182 anatomical structures included in Grant's Dissector, a widely used textbook for anatomical dissection. Furthermore, a sample of these PubMed-derived ranks had a highly significant, positive correlation with ranks derived from a consensus of experts. Similar results were obtained when PubMed searches were restricted to journals that focus on applying knowledge in a clinical setting. Our study provides a potential new tool for anatomical educators who are aligning their basic science curricula with the clinical knowledge expected of medical graduates.

The Short Neck: Challenges and Techniques.

Establishing a pleasant cervical contour in short-neck patients is of one the most difficult challenges for a facial plastic surgeon. Subplatysmal volume reduction, platysma tightening, and skin distribution adequately coupled with the middle third facelift are the pillars of the surgical approach. Additionally, treating the small chin, which is frequently observed in these patients, improves the overall result. In this paper, an objective method to define short-neck patients is offered. The applied surgical anatomy of the neck is revised. Innovative strategies to treat the supra and infrahyoid subplatysmal structures are presented, including the sternohyoid muscles plicature and the use of the interplatysmal/subplatysmal fat flap. A novel chin augmentation technique, using a subperiosteal en bloc fat graft is also introduced. A modified deep plane approach is described, including a continuous suture of the middle third fasciocutaneous flap. A combined lateral platysma tensioning with the sternocleidomastoid rejuvenation is demonstrated. Lastly, the hemostatic net is revisited as a critical approach to resolve the defying skin accommodation.

Anatomy of Neck Muscles, Spaces, and Lymph Nodes.

The following article details the muscular anatomy of the head and neck, including insertion, origin, action and innervation, organized by anatomic subunit and/or major action. This article also describes the spaces of the head and neck, including boundaties and contents. Finally, cervical lymph nodes are addressed according to anatomic location and lymphatic drainage.

Root of the Neck and Extracranial Vessel Anatomy.

The root of the neck is the junctional anatomic structure between the thoracic inlet, the axilla, and the lower neck. The detailed radiological anatomy of this critical area is discussed in this review.

Cranial ecomorphology of turtles and neck retraction as a possible trigger of ecological diversification.

Turtles have a highly modified body plan, including a rigid shell that constrains postcranial anatomy. Skull morphology and neck mobility may therefore be key to ecological specialization in turtles. However, the ecological signal of turtle skull morphologies has not been rigorously evaluated, leaving uncertainties about the roles of ecological adaptation and convergence. We evaluate turtle cranial ecomorphology using three-dimensional geometric morphometrics and phylogenetic comparative methods. Skull shape correlates with allometry, neck retraction capability, and different aquatic feeding ecologies. We find that ecological variables influence skull shape only, whereas a key functional variable (the capacity for neck retraction) influences both shape and size. Ecology and functional predictions from three-dimensional shape are validated by high success rates for extant species, outperforming previous two-dimensional approaches. We use this to infer ecological and functional traits of extinct species. Neck retraction evolved among crownward stem-turtles by the Late Jurassic, signaling functional decoupling of the skull and neck from the shell, possibly linked to a major episode of ecomorphological diversification. We also find strong evidence for convergent ecological adaptations among marine groups. This includes parallel loss of neck retraction, evidence for active hunting, possible grazing, and suction feeding in extinct marine groups. Our large-scale assessment of dietary and functional adaptation throughout turtle evolution reveals the timing and origin of their distinct ecomorphologies, and highlights the potential for ecology and function to have distinct effects on skull form.

Tartarugas tem um plano corpóreo bastante modificado, que inclui um casco rígido que restringe sua anatomia pós-craniana. Portanto, a morfologia craniana e a mobilidade do pescoço devem ser centrais nas especializações ecológicas de tartarugas. No entanto, o sinal ecológico das diferentes morfologias de crânio de tartarugas não foi ainda rigorosamente avaliado, deixando incertezas sobre os papéis de adaptações ecológicas e convergência. Avaliamos a ecomorfologia craniana de tartarugas utilizando morfometria geométrica tridimensional e métodos filogenéticos comparativos. A forma craniana correlaciona com alometria, capacidade de retração do pescoço e diferentes ecologias alimentares aquáticas. Encontramos que variáveis ecológicas influenciam apenas a forma do crânio, enquanto uma importante variável funcional (a capacidade de retração do pescoço) influencia tanto a forma como o tamanho do crânio. Predições ecológicas e funcionais para espécies viventes a partir de formas tridimensionais são validadas com altas taxas de sucesso, superando abordagens bidimensionais. Utilizamos isso para inferir traços ecológicos e funcionais de espécies extintas. A retração do pescoço evoluiu em linhagens extintas mais próximas à origem do grupo-coronal durante o Jurássico Final, indicando uma dissociação funcional entre crânio e pescoço do casco, algo possivelmente ligado a um importante episódio de diversificação ecomorfológica. Também encontramos forte evidência para adaptações ecológicas convergentes em grupos marinhos. Isso inclui a perda paralela da retração do pescoço, evidência de caça ativa, alimentação por sucção, além de possível preferência por plantas aquáticas em grupos marinhos extintos. Nosso estudo de larga-escala sobre adaptações funcionais e relacionadas à dieta ao longo da evolução de tartarugas revela o tempo e origem de suas distintas ecomorfologias, e destaca ainda o potencial de ecologia e função terem efeitos distintos sobre a forma craniana.

Application of the new 'XU-line' in the dynamic ultrasonographic evaluation of the spatial displacement of anterior cervical tissues for airway management: protocol for a prospective observational study.

INTRODUCTION: Patients with cervical spondylosis have a high incidence of difficult airway, and unpredicted difficult intubation may be life-threatening. Traditional predictors and imaging data may suggest a difficult airway, but these data have limited predictive value, with low sensitivity and specificity. Ultrasonography is a non-irradiating, reproducible, inexpensive and simple tool that provides good imaging of the cervical soft tissue for airway assessment. This study will use the new 'XU-line' in the dynamic ultrasonographic airway evaluation of the spatial displacement of the anterior cervical tissues to determine whether preoperative ultrasonographic assessment of the neck anatomy can predict difficult airway. METHODS AND ANALYSIS: This prospective, observational study will be conducted in a single centre. Four hundred and eleven patients scheduled for anterior cervical decompression and fusion under general anaesthesia will be recruited. The parallel trunk reference line through the mentum is defined as the XU-line, and the spatial displacement of the anterior cervical soft tissue relative to the XU-line at six anatomical levels in the transverse plane and two distances in the sagittal plane will be measured on ultrasonography with the patient in the supine position and the sniff position. The spatial displacement distances of soft tissue structures relative to the XU-line will be compared between the 'easy intubation' and 'difficult intubation' groups (in accordance with the Cormack-Lehane classification). Receiver operating characteristic curves will be used to determine the sensitivity and specificity of the 'difficulty prediction capability' of each ultrasonographic and physical measurement. Multiple logistic regression analysis will be performed to determine the independent predictors of difficult intubation. ETHICS AND DISSEMINATION: Ethical approval for this study has been obtained from the Peking University Third Hospital Medical Science Research Ethics Committee. The results of this study will be disseminated via a peer-reviewed publication and national and international conferences and workshops. TRIAL REGISTRATION NUMBER: ChiCTR2000034446.