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Interest in the relational anatomy of the anterior neck among spine surgeons increased after the popularization of anterior cervical discectomy and fusion in the 1950s. Five surface landmarks and their relationship to specific spinal levels have been routinely described, comprising the angle of the mandible for the C2-C3 interspace, the hyoid bone for the C3 body, the thyroid cartilage for the C4-C5 disc, and the cricoid cartilage and carotid tubercle for the C6 body. We aimed to investigate the origins of these anatomic relationships and their application in modern practice., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Purpose: The current supraomohyoid neck dissection (SOHND) is performed above the omohyoid muscle to dissect levels I, II, and III in the levels of cervical lymph nodes. However, the anatomical boundary between levels III and IV is the inferior border of the cricoid cartilage. We investigated the anatomical relationship between the omohyoid muscle and cricoid cartilage using contrast-enhanced CT (CE-CT) images to assess the validity of the current SOHND., Methods: CE-CT images of the head and neck regions in patients were reviewed. The patients were divided into two groups: "malignant tumors" and "others". The vertebral levels corresponding to the positions of anatomical structures such as the intersection of the omohyoid muscle and internal jugular vein (OM-IJ), and the inferior border of the cricoid cartilage (CC), were recorded., Results: The OM-IJ was located around the seventh cervical to the first thoracic vertebra. There was a significant difference between the malignant tumor and others groups in females (p = 0.036). The CC was located around the sixth to seventh cervical vertebrae. There was a significant sex difference in each group (malignant tumor: p < 0.0001; others: p = 0.008). Both sexes tended to have lower OM-IJ than CC, and females had significantly lower OM-IJ than males., Conclusion: This study provides clear anatomical evidence showing the difference between the SOHND dissection area and levels I, II, and III. It could be considered that in most cases SOHND invades level IV, not just levels I, II, and III, especially in female patients., (© 2024. The Author(s).)

The thyrohyoid muscle belongs to the infrahyoid group located in the carotid triangle. It normally originates from thyroid cartilage and inserts into hyoid bone. Quite often, it is continuous with the sternohyoid muscle. Furthermore, there are variants that have their origin in the cricoid cartilage only, however, this occurs very rarely. During anatomical dissection, a two-headed variant of this muscle was found. One head had its origin in the cricoid cartilage and the other in the thyroid cartilage. This variant of thyrohyoid had not been previously described in the available literature. Therefore, we believe that it may be referred to as the cricothyrohyoid muscle. As the thyrohyoideus is often used as a landmark during surgical procedures in the prelaryngeal area and as a muscle graft, a thorough knowledge of its anatomy and variation is extremely important. We speculate that the two-headed version of this muscle may be problematic during surgical procedures in this region, however, it may also provide more options as a muscular graft., (© 2024. The Author(s).)

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., Competing Interests: The authors have no funding and conflicts of interest to disclose., (Copyright © 2024 the Author(s). Published by Wolters Kluwer Health, Inc.)

The Aim of the Study: Was to develop the age determination's technology by the morphometric features of the human cricoid cartilage using a regression analysis method. Cricoid cartilages of 65 variously-aged males were examined. The number of histomorphometric parameters equal 16 for each sample were determined and measured on the histological sections. A descriptive statistical processing of data using the regression analysis method was done, as a result of which the model of age determination was developed. This model has a high predictive accuracy, where the prediction error was less than 5 years in 64.62% of cases. The practical use of this model may be limited by the morphometric parameters' number translating complication to calculate the formula. The developed method can be improved while increasing the sample and conducting further statistical processing, and in the future it can be used in the age determination in forensic medical examination.

Background: The cricothyroid membrane (CTM) is the most important anatomic structure when performing emergency front-of-neck access (FONA) procedures. Adolescence is a period of rapid morphologic change in laryngeal structures, including the CTM. We hypothesized that the adolescent CTM would be sufficiently different from pediatric or adult anatomy to merit special consideration in FONA., Objective: The aim of the study was to define the procedurally relevant CTM anatomy in an adolescent population., Methods: This was a retrospective, multicenter cohort study composed of patients who underwent a diagnostic computed tomography scan during routine clinical care. Inclusion criteria were ages 16 to 19 years and a computed tomography of the neck with or without contrast. The primary outcome was CTM height measured in the midsagittal plane using electronic calipers., Results: One hundred thirty-four imaging studies met inclusion criteria. The average CTM height was strongly associated with age and ranged between 5.4 and 6.2 mm in male adolescents and 4.6 and 5.8 mm in female adolescents. We predicted that standard cuffed endotracheal and tracheostomy tubes recommended for FONA procedures (5.0- and 6.0-mm devices) could potentially fail for most patients in our cohort., Conclusions: The adolescent CTM is smaller than previously recognized. We recommend having a variety of equipment sizes readily available at any site where airway management in adolescents may occur., Competing Interests: Disclosure: The authors declare no conflict of interest., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

The primary objective of this study is to compare the effectiveness of cricoid pressure (CP) and paralaryngeal pressure (PLP) on occlusion of eccentric esophagus in patients under general anesthesia (GA). Secondary objectives include the prevalence of patients with central or eccentric esophagus both before and after GA, and the success rate of CP in occluding centrally located esophagus in patients post GA. Fifty-one ASA physical status I and II patients, undergoing GA for elective surgery were enrolled in this study. Ultrasonography imaging were performed to determine the position of the esophagus relative to the trachea: (i) before induction of GA, (ii) after GA before external CP maneuver, (iii) after GA with CP, and (iv) after GA with PLP. CP was applied to all patients whilst PLP via fingertip technique was only applied to patients with an eccentric esophagus. Among a total of 51 patients, 28 of them (55%) had eccentric esophagus pre GA, while this number increase to 33 (65%) after induction of GA. CP success rate was 100% in 18 patients with central esophagus post GA versus 27% in 33 patients with eccentric esophagus post GA (P<0.00001). Overall success rate for CP was 53%. In 33 patients with eccentric esophagus anatomy post GA, PLP success rate was 30% compared with 27% with CP (P=1.000). Ultrasound guided PLP fingertips technique was not effective in patients with an eccentrically located esophagus post GA. Ultrasound guided CP achieved 100% success rate in patients with a centrally located esophagus post GA., (© 2021. Springer Nature B.V.)

Objective: Define the length of the subglottis and trachea in children to predict a safe intubation depth., Methods: Patients <18 years undergoing rigid bronchoscopy from 2013 to 2020 were included. The carina and inferior borders of the cricoid and true vocal folds were marked on a bronchoscope and distances were measured. Patient age, weight, height, and chest height were recorded. Four styles of cuffed pediatric endotracheal tubes (ETT) were measured and potential positions of each cuff and tip were calculated within each trachea using five depth of intubation scenarios. Multivariate linear regression was performed to identify predictors of subglottic and tracheal length., Results: Measurements were obtained from 210 children (141 male, 69 female), mean (SD) age 3.21 (3.66) years. Patient height was the best predictor of subglottic length (R 2 : 0.418): Length sg (mm) = 0.058 * height (cm) + 2.8, and tracheal length (R 2 : 0.733): Length t (mm) = 0.485 * height (cm) + 21.3. None of the depth of intubation scenarios maintained a cuff-free subglottis for all ETT styles investigated. A formula for depth of intubation: Length di (mm) = 0.06 * height (cm) + 8.8 found that no ETT cuffs would be in the subglottis and all tips would be above the carina., Conclusion: Current strategies for determining appropriate depth of intubation pose a high risk of subglottic ETT cuff placement. Placing the inferior border of the vocal cords 0.06 * height (cm) + 8.8 from the superior border of the inflated ETT cuff may prevent subglottic cuff placement and endobronchial intubation., Level of Evidence: 4 Laryngoscope, 132:S1-S10, 2022., (© 2021 The American Laryngological, Rhinological and Otological Society, Inc.)

Objectives: The purpose of this study was to better understand the effects of stitch placement on arytenoid medialization by measuring normative cricoarytenoid joint anatomy and changes in arytenoid position when varying arytenopexy stitch configuration., Methods: This adult human larynx study was done in two parts. First, measurements of the cricoid and arytenoid cartilage anatomy relevant to cricoarytenoid joint function were made in 45 preserved larynges (26 male (M), 19 female (F)) using digital calipers. Second, the arytenoids of six fresh larynges ( three M, three F) were sutured to the cricoid using various arytenopexy-stitch placements ranging from inferior-lateral to superior-medial, and the resulting arytenoid positions were compared by measuring medial displacement of the arytenoid body and change in glottal configuration from macro still images using Image J. Paired t-tests were used to compare the results., Results: Cartilage and joint facet dimensions showed differences between males (M) and females (F). Cricoid facet lengths averaged 9.3 mm (M) and 7.1 mm (F), and widths averaged 4.9 mm (M) and 4.0 mm (F). The arytenoid facet widths averaged 10.5 mm (M) and 9.7 mm (F). Average distances between cricoid facets were 11.8 mm for both males and females. Securing the arytenoid superior-medially on the cricoid facet produced more medialization (2.2 mm vs 1.0 mm, P < .001) and better glottic aperture configuration (9.5° vs 2.7°, P < .001) than securing the arytenoid inferior-laterally on the facet., Conclusions: Anatomic consistency in cricoarytenoid anatomy provides reliable surgical landmarks for ideal placement of an arytenopexy suture to optimally reposition the arytenoid cartilage. Optimal arytenoid medialization can be accurately reproduced with an arytenopexy-suture that is placed superior-medially on the cricoid facet., Level of Evidence: NA Laryngoscope, 131:2540-2544, 2021., (© 2021 The American Laryngological, Rhinological and Otological Society, Inc.)

Background: Accurate identification of the cricothyroid membrane is crucial for successful cricothyroidotomy. The aim of this study was to compare the conventional downward and modified upward laryngeal handshake techniques in terms of accuracy to identify the cricothyroid membrane in nonobese female patients., Methods: In 198 anesthetized female patients, the cricothyroid membrane was identified by either the conventional downward laryngeal handshake technique (n = 99) or the modified upward laryngeal handshake technique (n = 99). According to the conventional downward laryngeal handshake technique, the cricothyroid membrane was identified by palpating the neck downward from the greater cornu of the hyoid bone, thyroid laminae, and cricoid cartilage. According to the modified upward laryngeal handshake technique, the cricothyroid membrane was located by moving up from the sternal notch. The primary outcome was the accuracy of identifying the cricothyroid membrane. Secondary outcomes included the accuracy of midline identification and time taken to locate what participants believed to be the cricothyroid membrane. The primary and secondary outcomes according to the technique were analyzed using generalized estimating equations., Results: The cricothyroid membrane could be identified more accurately by the modified upward laryngeal handshake technique than by the conventional downward technique (84% vs 56%, respectively; odds ratio [OR], 4.36; 95% confidence interval [CI], 2.13-8.93; P < .001). Identification of the midline was also more accurate by the modified laryngeal handshake than by the conventional technique (96% vs 83%, respectively; OR, 4.98; 95% CI, 1.65-15.01; P = .004). The time taken to identify the cricothyroid membrane was not different between the conventional and modified techniques (20.2 [16.2-26.6] seconds vs 19.0 [14.5-26.4] seconds, respectively; P = .83)., Conclusions: The modified upward laryngeal handshake technique that involved tracing the trachea and laryngeal structures upward from the sternal notch was more accurate in identifying the cricothyroid membrane than the conventional downward technique in anesthetized female patients., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 International Anesthesia Research Society.)

Purpose: This study aims to determine laryngeal dimension in relation to all three transcutaneous injection laryngoplasty (TIL) approaches (thyrohyoid, transthyroid and cricothyroid) using three-dimensionally reconstructed Computed Tomography (CT) scan and compare the measurements between sex, age group and ethnicity., Methods: CT scans of the neck of two hundred patients were analysed by two groups of raters. For thyrohyoid approach, mean distance from the superior border of the thyroid cartilage to the laryngeal cavity (THd) and mean angle from the superior border of the thyroid cartilage to mid-true cords (THa) were measured. For transthyroid approach, mean distance from mid-thyroid cartilage to mid-true cords (TTd) and Hounsfield unit (HU) at mid-thyroid cartilage (TTc) were measured. For cricothyroid approach, mean distance from the inferior border of the thyroid cartilage to the laryngeal cavity (CTd) and mean angle from the inferior border of the thyroid cartilage to mid-true cords (CTa) were measured., Results: There were statistically significant differences between males and females for all measurements except for CTa (p < 0.0001). No significant difference across age groups and ethnicities were found for all three approaches (p > 0.05). There was a significant fair positive correlation between age and TTc (p = 0.0002). For all measurements obtained, there were moderate to excellent inter-group consistency and intra-rater reliability., Conclusion: This study demonstrated a significant sex dimorphism that may influence the three TIL approaches except for needle angulation in the cricothyroid approach. The knowledge of laryngeal dimension is important to increase success in TIL procedure., (© 2021. Springer-Verlag France SAS, part of Springer Nature.)

Background: Emergency front-of-neck airway rescue is recommended in a can't intubate, can't oxygenate clinical scenario. Cannula cricothyroidotomy has been reported as having a high failure rate. Our primary aim was to estimate the angle of the trachea in relation to the horizontal axis in a simulated emergency front-of-neck airway rescue position. Our secondary aims were to estimate the optimal cannula angle of approach and evaluate the anatomical relationship of the cricothyroid membrane (CTM) to adjacent structures. We also assessed whether the CTM lies above or below the neck midpoint, a point equidistant from the suprasternal notch (SSN), and the chin surface landmarks. All measurements were compared between the male and female subjects., Methods: Subjects having elective computed tomography of their thorax were consented to have extension of the computed tomography to include their neck. A preliminary radiation dose and risk assessment deemed the additional radiation to be of very low risk (level IIa). Subjects were positioned supinely on the computed tomography table. Standard neck extension was achieved by placing a pillow under the scapulae and a rolled towel under the neck to simulate emergency front-of-neck airway rescue positioning., Results: Fifty-two subjects were included in this study: 31 men and 21 women. The mean angle of the trachea in relation to the horizontal axis was 25.5° (95% confidence interval [CI], 21.8-29.1) in men and 14.0° (95% CI, 11.5-16.5) in women. The mean minimum angles required for hypothetical cannula cricothyroidotomy for men and women were 55.2° (95% CI, 51.8-58.7) and 50.5° (95% CI, 45.4-55.6), respectively. The CTM was located lower in the neck in men compared to women. The CTM was located below the neck midpoint in 30 of 30 (100%) male subjects and 11 of 20 (55%) female subjects (P < .001)., Conclusions: The trachea angulates posteriorly in a simulated emergency front-of-neck airway rescue position in supine subjects and to a greater degree in men compared to women (P < .001). The minimum angle required for hypothetical cannula cricothyroidotomy was >45° in the majority (75%) of subjects studied. A steeper cannula angle of approach may be more reliable and warrants further clinical study. If airway anatomy is indistinct and performing a vertical scalpel cricothyroidotomy, consideration should be given to performing this incision lower in the neck in men compared to women., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 International Anesthesia Research Society.)

Objectives: The recommended front of neck access procedure in can't intubate, can't oxygenate scenarios relies on palpation of the cricothyroid membrane (CTM), or dissection of the neck down to the larynx if CTM is impalpable. CTM palpation is particularly challenging in obese patients, most likely due to an increased distance between the skin and the CTM (CTM depth). The aims of this study were to measure the CTM depth in a representative clinical sample, and to quantify the relationship between body mass index (BMI) and CTM depth., Methods: This is a retrospective analysis of 355 clinical CT scans performed at a teaching hospital over an 8-month period. CTM depth was measured by two radiologists, and mean CTM depth calculated. Age, gender, height and weight were recorded, and BMI calculated. Linear relationships between patient characteristics and CTM depth were assessed in order to derive a predictive equation for calculating CTM depth. The variables included for this model were those with a strong association with CTM depth, that is, a p value of 0.10 or less., Results: Mean CTM depth was 8.12 mm (IQR 6.36-11.70). There was no association between CTM depth and sex (β -0.33, 95% CI -1.33 to 0.68, p=0.53), height (cm) (β 0.01, 95% CI -0.05 to 0.06, p=0.79) or age (years) (β -0.01, 95% CI 0.10 to 0.15, p=0.62). Increasing weight (kg) (β 0.12, 95% CI 0.10 to 0.15, p<0.001) and BMI (kg/m 3 ) (β 0.52, 95% CI 0.44 to 0.60, p<0.001) were strongly associated with CTM depth. Predicted CTM depth increased from 6.4 mm (95% CI 4.9 to 8.1) at a BMI of 20 kg/m 2 to 16.8 (95% CI 13.7 to 20.1) at BMI 40 kg/m 2 ., Conclusion: CTM depth was strongly associated with BMI in a retrospective analysis of patients having clinical CT scans., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Objectives: To measure the dimensions of the cricoid cartilage in adults and to investigate the age-related change of the dimensions of the cricoid cartilage., Methods: After performing the multiplanar reconstruction and correcting the slant of the cervical computed tomography scans, the transverse and anteroposterior internal diameters of the inlet (TD-in and APD-in) and outlet (TD-out and APD-out) of the cricoid cartilage were measured, respectively. The angle between the arch and lamina of the cricoid cartilage in the middle sagittal plane was measured. The ratios of transverse to anteroposterior diameter for the inlet (Ratio-in) and outlet (Ratio-out) of the cricoid cartilage were calculated, respectively., Results: A total of 1200 adults were included in this study, with 600 males and 600 females. The TD-in is the smallest cricoid diameter and the APD-in is the largest cricoid diameter. The mean cricoid diameters and the cricoid angle in males were larger than those in females. The cricoid inlet is oval shaped and the cricoid cartilage is "funnel-shaped" in the middle sagittal plane. The shape of the outlet of the cricoid cartilage varies greatly among individuals. In males, the APD-in and APD-out were negatively correlated with age while the Ratio-in and Ratio-out was positively correlated with age. In females, the APD-out were negatively correlated with age while the Ratio-out was negatively correlated with age., Conclusions: The dimensions of the cricoid cartilage change as age advances in adult population and the sexual dimorphism of the cricoid outlet occurs after 50 years old.

Application of cricoid pressure (CP) during rapid sequence induction and intubation sequence has been a "standard" of care for many decades, despite limited scientific proof of its efficacy in preventing pulmonary aspiration of gastric contents. While some of the current rapid sequence induction and intubation guidelines recommend its use, other international guidelines do not, and many clinicians argue that there is insufficient evidence to either continue or abandon its use. Recently published articles and accompanying editorials have reignited the debate on the efficacy and safety of CP application and have generated multiple responses that pointed out the various (and significant) limitations of the available evidence. Thus, a critical discussion of available data must be undertaken before making a final clinical decision on such an important patient safety issue. In this review, the authors will take an objective look at the available scientific evidence about the effectiveness and safety of CP in patients at risk of pulmonary aspiration of gastric contents. We suggest that current data are inadequate to impose clinical guidelines on the use of CP because we acknowledge that currently there is not, and there may never be, a method to prevent aspiration in all patients. In addition, we reiterate that a universally accepted medical-legal standard for approaching the high-risk aspiration patient does not exist, discuss the differences in practice between the US and international practitioners regarding use of CP, and propose 5 recommendations on how future studies might be designed to obtain optimal scientific evidence about the effectiveness and safety of CP in patients at risk for pulmonary aspiration.

Purpose: Conventional palpation techniques for cricothyroid membrane (CTM) identification are inaccurate and unreliable. Ultrasound plays a multi-faceted role in airway management, however there is limited literature around its use for CTM identification prior to cricothyrotomies. This review sought to compare ultrasound to palpation in the general population, identify its indications in subjects with ill-defined neck anatomy, and determine its role in defining neck anatomy., Methods: Two reviewers independently assessed titles, abstracts and full-text English articles through the Ovid Medline and EMBASE databases. Studies related to ultrasound for CTM assessment and/or cricothyrotomy in subjects older than 12 years were included., Results: Fourteen studies were selected. Compared to palpation, ultrasound has greater accuracy, but longer CTM identification times in those with normal airway anatomy. Interestingly, ultrasound offers comparable times to palpation in patients with difficult airways. Ultrasound also helps define anatomical parameters in the neutral and extended neck positions thereby underscoring the importance of neck positioning during cricothyrotomies and confirming consensus-based incision recommendations set by the Difficult Airway Society., Conclusion: Ultrasound appears to be superior to palpation for CTM localization especially in those with difficult airway anatomy and objectively defines neck anatomy. Its pre-emptive use should be incorporated during difficult airway management., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Objectives: Determine whether the insertion site of the recurrent laryngeal nerve (RLN) occurs at a predictable distance from the midline trachea, to help guide safe dissection during thyroid surgery., Design: Prospective clinical trial. At the inferior edge of the cricoid cartilage, we measured the distance from mildline trachea to the RLN insertion site., Setting: Single institution., Participants: 50 consecutive patients undergoing thyroid surgery., Main Outcome Measures: Distance from midline trachea to laryngeal insertion of RLN., Results: The study population included 36 women and 14 men, with 72 total nerves measured. The average distance-to-midline + standard deviation (range) of the RLN was 20.7 + 2.3 (17-26) mm in women compared to 26.3 + 2.1 (22-32) mm in men., Conclusion: The insertion point of the RLN into the larynx at the level of inferior border of the cricoid cartilage can be reliably predicted, to facilitate early identification of the RLN during thyroid surgery., (© 2020 John Wiley & Sons Ltd.)

The aim of this study was to evaluate the effectiveness of cricoid and paralaryngeal force for oesophageal entrance occlusion during induction of anaesthesia. Seventy-four patients were included in this randomised, crossover study. The relative position of the glottis and outer anteroposterior diameter of the upper oesophageal entrance were assessed at baseline, after the application of 30 N cricoid and paralaryngeal force, and after induction of anaesthesia. The occlusion rate of the oesophageal entrance with cricoid and paralaryngeal force was assessed during direct laryngoscopy. The relative position of the upper oesophageal entrance to the glottis changed in 45 out of 74 patients after induction of anaesthesia and during direct laryngoscopy compared with the awake state. The application of cricoid and paralaryngeal force decreased the mean (SD) diameter of the upper oesophageal entrance to a similar degree in awake (8.5 (2.1) mm to 6.4 (1.7) mm and 6.5 (1.6) mm, respectively; p < 0.001) and anaesthetised (8.7 (2.2) mm to 6.5 (1.7) mm and (6.7 (1.9) mm, respectively; p < 0.001) states. During direct laryngoscopy, the occlusion rate of the oesophageal entrance was greater with cricoid compared with paralaryngeal force (46/74 vs. 26/74, respectively; p = 0.002). The relative position of the upper oesophageal entrance to the glottis may change after induction of anaesthesia and during direct laryngoscopy. Cricoid and paralaryngeal force both decrease the diameter of the upper oesophageal entrance in awake and anaesthetised states. Occlusion of the oesophageal entrance is achieved more frequently with cricoid force compared with paralaryngeal force during direct laryngoscopy., (© 2019 Association of Anaesthetists.)

Background: The rigid cricoid cartilage is functionally the narrowest portion of the larynx. There is some controversy over the shape of the pediatric cricoid cartilage in the transverse plane. It is important to understand the development of the cricoid cartilage so that endo-traceheal tubes can be used more safely., Aim: To determine changes in the internal diameter and shape of the cricoid cartilage during development and explore the implications of those changes for the selection of ETT type and size for children., Methods: The cervical computed tomography scans were reviewed in patients aged 1-20 years. After performing the multiplanar reconstruction and correcting the slant, the transverse and anteroposterior internal diameters of the inlet and outlet of the cricoid cartilage were measured, respectively. The angle between the arch and the lamina of the cricoid cartilage in the middle sagittal plane was measured. The ratios of transverse to anteroposterior diameter for the inlet and outlet of the cricoid cartilage were calculated, respectively., Results: In females, the internal diameters of the cricoid cartilage increased linearly with age. In males, the internal diameters of the cricoid cartilage exhibited a growth spurt during adolescence. The transverse diameter of the inlet was the smallest diameter of the cricoid cartilage, and the predicting formula of the transverse diameter of the inlet for children aged 1-12 was 0.4 × age (year) + 5.1, R 2  = .758. The angle between the arch and lamina of the cricoid cartilage and the ratios of transverse to anteroposterior diameter correlated weakly with age., Conclusion: The transverse inner diameter of the inlet is the smallest diameter of the cricoid cartilage. The "funnel shape" of the cricoid cartilage remains unchanged during development. The outer diameter should be considered when selecting an endotracheal tube., (© 2019 John Wiley & Sons Ltd.)

Background: Emergency front of neck access in a "can't intubate can't oxygenate" scenario in pediatrics is rare. Ideally airway rescue would involve the presence of an ear, nose, and throat surgeon. If unavailable however, responsibility lies with the anesthesiologist and accurate identification of anterior neck structures is essential for success., Aim: We assessed anesthesiologists' accuracy in identification of the pediatric cricothyroid membrane by digital palpation in three predefined age groups (37 weeks to <1 year old, 1-8 years old, and 9-16 years old) and whether accuracy improved with repetition. We also investigated a novel hypothetical vertical skin incision strategy to successfully expose the cricothyroid membrane., Methods: We asked anesthesiologists to identify the location of the cricothyroid membrane of anesthetized children in the extended neck position. Accuracy was defined as a mark made within the margins of the cricothyroid membrane using ultrasound as a reference standard. The position of the cricothyroid membrane relative to the neck midpoint, between the suprasternal notch and mentum, was defined for each child. Using this neck midpoint, we determined the hypothetical vertical skin incision lengths required to successfully expose the cricothyroid membrane ("midpoint incision")., Results: Ninety-seven patients were included in this study. There were 14, 58, and 25 patients recruited across the three predefined groups. Accurate anesthesiologist identification of the location of the cricothyroid membrane occurred in 29.4%, 28.6%, and 38.2% of attempts, respectively. The majority of inaccurate assessments (64.1%) were below the cricothyroid membrane. There was no improvement in accuracy with repetition. Hypothetical "midpoint incision" lengths of 20, 30, and 35 mm were required., Conclusion: Significant anesthesiologist inaccuracy exists in locating the cricothyroid membrane in children of all ages. This has implications for the technical approach to emergency front of neck access and how we teach the management of "can't intubate can't oxygenate" in pediatric practice., (© 2019 John Wiley & Sons Ltd.)

Background: Knowing the likely depth to the airway before emergency cricothyroidotomy may improve success in cases where it cannot be measured. Our aim was to measure the depth to the airway at the cricothyroid membrane by ultrasound in a large group of adult patients., Method: Prospective, observational study in two centres, Oxford and Gloucester. Patients presenting for a large variety of surgical operations were studied. Patients under 18 years; pregnant; critically ill; had a history of neck surgery were not included. Ultrasound examination was performed pre-operatively while participants lay supine with their head and neck extended, with light transducer pressure. We measured depth to the airway lumen in mm; age; weight; height and sex., Results: In total 352 patients were studied. We found that depth to the airway lumen strongly correlated with weight (r = 0.855, P < 0.001) and to a lesser extent body mass index (r = 0.781, P < 0.001). Statistical analysis produced an equation to predict upper 95% CI of depth to the airway from the patient's weight: Depth to the airway lumen in mm = (0.13 × weight in kg) + 0.86., Conclusions: If ultrasound measurement is not possible before emergency cricothyroidotomy, the clinician could use our results to predict the depth to the airway by using the patient's weight. If the upper 95% CI were used as the depth of incision, it would enter the airway in 39 out of 40 patients of that weight, without damage to posterior structures in those with a shallower airway., (© 2019 The Acta Anaesthesiologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.)

Background: Identification of the cricothyroid membrane is frequently inaccurate in females because of less distinct anatomy compared with males. Supraglottic airway devices cause ventral displacement of the laryngeal structures. We investigated if this would impact on the accuracy of cricothyroid membrane identification using palpation., Methods: We recruited 64 adult females who underwent assessment by volunteer participants with and without a sited i-gel ® supraglottic airway device. The primary outcome was accuracy in identifying the cricothyroid membrane. Secondary outcomes included distance from participant estimate to actual cricothyroid membrane location and perceived difficulty using a visual analogue scale. Ultrasound images were analysed to determine the effect of the i-gel ® on the anatomical structures relevant to cricothyroidotomy., Results: The cricothyroid membrane was identified correctly in 42/64 subjects with the i-gel ® in place (66%) vs 23/64 of controls (36%; P<0.001, mean difference 30%; 95% confidence interval, 12-47%). VAS (P<0.001) and distance to the cricothyroid membrane (P<0.001) decreased in the intervention group. Analysis of the ultrasound image series showed a reduction in the mean angle between the cricothyroid membrane and anterior wall of the trachea in the i-gel ® group, because of the more ventral position of the cricoid cartilage compared with control images (166° vs 151°, P<0.001)., Conclusions: The presence of the i-gel ® improved accuracy of identifying the cricothyroid membrane using palpation in females. The cricoid cartilage was pushed ventrally by the i-gel ® in the hypopharynx, creating a more palpable prominence. It may therefore be advantageous to retain a sited supraglottic airway, rather than remove it, before performing emergency cricothyroidotomy., (Copyright © 2019 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.)

The agenesis of one or both upper thyroid horns (UTH) cannot be considered rare with an incidence ranging between 0.8-9.4%. Studies so far have mostly described frequencies, yet surveys on its morphology and traumatology are missing. It is unknown to what extent this anatomical variant impacts the overall symmetry of the larynx. For the trauma reconstruction after cervical trauma this knowledge is required as an asymmetric larynx can show a different fracture pattern. In this investigation, larynxes with unilateral (n=21)/bilateral (n=5) agenesis of the upper thyroid horn(s) and a control group with regular larynxes (n=23) were juxtaposed. Various measurements were taken after μ-CT scanning. In total 10 distances/angles for the thyroid cartilage and 8 for the cricoid cartilage were compared. Using intra-individual and matched pair comparisons the symmetry was assessed. The results of this investigation showed significant differences in the intra-individual and pairwise comparison for the opening angle and the length of the thyroid alae although the lateral inclination of the thyroid alae showed no significant difference. Combining these three parameters into one symmetry score, the comparison was not significant. This research demonstrates that neither unilateral nor bilateral agenesis of the UTH is related to a structural disbalance of the larynx. Thus, different fracture patterns or vulnerabilities are not to be expected., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Purpose: To measure the age-dependent changes of anatomical positions and relations between the trachea, cricoid cartilage (CC), and innominate artery (IA) in adults by computed tomography (CT)., Methods: A retrospective cohort reviewing images of 127 consecutive adult patients who underwent CT angiography (CTA) of the neck. The trachea-to-IA (T-IA) distance was measured as the minimal horizontal distance between them. The vertical distance between the CC and the IA was measured between the axial section, demonstrating the CC's inferior border to the axial section at the level of the T-IA measurement., Results: Images of 125 patients (median age 53 years, range 18-89; 74 males) were reviewed. The mean T-IA distance was 2.3 ± 1.1 mm for males and 1.7 ± 0.9 mm for females (P = 0.002). The vertical C-IA distance was 44.2 ± 11.4 mm and 49.5 ± 12.5 mm for males and females, respectively (P = 0.01). Age correlated negatively with the vertical C-IA distance (P < 0.0001) and positively with the T-IA distance (P < 0.0001). The rate of IA variants was 23.2%, with no significant difference between the measurements of distances among patients with or without IA variants., Conclusions: This is the first description of the relationships between the trachea, CC, and IA distances in adults as depicted on CTA. The T-IA distance becomes larger while the T-CC distance becomes shorter with age.

Background: The aim of this study was to investigate the success rates of ultrasound (US) and palpation methods in identifying the cricothyroid membrane (CTM), and compare the results with the gold standard method-computed tomography (CT) scan., Methods: A total of 110 patients were included into the study. The midline was estimated by a single investigator using both the US and palpation methods from the prominence of the thyroid cartilage to the center of the sternal notch, and the distance was measured (in millimeters) between the two points: Point A (the midpoint of CTM) and Point B (the inferior process of thyroid cartilage). Furthermore, the distance between Point A and Point B was calculated using the CT images. Time taken to assess the CTM by using US and palpation methods were recorded. Moreover, difficulty in using the two methods was measured with the visual analog scale (VAS). In addition, demographic and morphometric characteristics of the patients were noted., Results: The CTM was detected accurately in 50 (45.5%) patients with palpation and 82 (74.5%) with US. In the Bland-Altman analysis, a better agreement was observed with US. The time to assess CTM was shorter with US than with palpation, p<0.001. The VAS scores for the palpation and US difficulty were 5.13+-1.1 and 3.32+-0.9 (p<0.001), respectively. While an increased neck circumference and thyromental distance were found to be independent risk factors for the success rates of determining the CTM by palpation, body mass index is an independent risk factor for US., Conclusion: Localization of the CTM is more accurate and easier with US than palpation. Furthermore, the results gathered with US are in a closer range to CT scan.

New observations from novel imaging techniques regarding the anatomy, dimensions, and shape of the pediatric airway have emerged and provide insight for potential changes in the clinical management of the airway in infants and children. These new findings are challenging the historical concepts of a funnel-shaped upper airway with the cricoid ring as the narrowest dimension. Although these tenets have been accepted and used to guide clinical practice in airway management, there are limited clinical investigations in children to support the validity of these concepts. Imaging modalities such as magnetic resonance imaging, computed tomography (CT) scanning, multi-detector CT imaging, and videobronchoscopy suggest the need to revisit the historical view of the pediatric airway. This manuscript reviews the historical evolution of pediatric airway studies, summarizes important scientific observations from recent investigations relevant to our clinical understanding of pediatric airway anatomy, and discusses the importance of these findings for pediatric airway management., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The cricoid cartilage serves as an anatomical reference for several surgical procedures for access to the airway. Additionally, it serves as an attachment point for muscles that move the vocal folds. We present a case where the cricoid cartilage arch is divided into distinct superior and inferior arches, with a fibrous membrane between them. We did not find any similar description to this case in the literature, which makes it unique to date. This type of variation is important knowledge for clinicians and surgeons during airway management in the anterior neck region. The presence of this variation could induce an error during a palpation of the thyroid and cricoid cartilages, realized in clinical examination and surgical or emergency procedures.

Objective: This anatomic study considers the feasibility of a posterior endoscopic approach to the cricoarytenoid joint (CAJ) by describing relationships between readily identifiable anatomic landmarks and the posterior CAJ space in cadaver larynges., Study Design: Anatomic study., Methods: Six adult cadaver larynges (2 male, 4 female) were studied. Digital calipers were used for measurements, and Image J software was used for angle calculations. All cricoarytenoid joints were injected with colored gel via a posterior approach using a 27-gauge needle., Results: The average age of the larynges studied was 78.7 ± 10 years. The average posterior CAJ space (pCAJs) length measured 4.95 ± 0.9 mm. The average distance from the superior aspect of the midline cricoid lamina (MCL) to the center of pCAJs and the corniculate cartilage (CC) to the center of the pCAJs were 8.35 ± 1.5 mm and 14.54 ± 1.9 mm, respectively. The average pCAJs angle of declination (AD) from the horizontal plane was 54° ± 6.2°. All 12 cricoarytenoid joints were successfully injected with colored gel via a posterior approach., Conclusions: The posterior CAJ space can be located surgically using readily identifiable anatomic landmarks. An understanding of this posterior CAJ anatomy may allow for more consistent intra-articular injection and support the development of other CAJ procedures for a range of disorders of vocal fold motion or malposition.

The purpose of this study was to evaluate the accurate identification of the cricothyroid membrane (CTM) by fifth grade dental students, before undergoing the relevant anesthesiology practicum. Moreover, we aimed to determine the educational effectiveness of the cricothyrotomy practicum in anesthesiology. Before the lecture and without prior notification, 119 students were provided with a photograph of a man's neck and instructed to attach a blue sticker to the cricothyrotomy puncture site and to a palpable tracheotomy trainer, after applying sufficient palpation. After this, students attended a 60-min lecture on the emergency airway management method. Two and 16 days after the lecture and practicum, students were presented with a new neck photograph and the tracheotomy trainer and asked again to place stickers (red stickers: at 2 days; green stickers: at 16 days) on the cricothyrotomy penetration site. The data were analyzed with an image processing software, by superimposing the 119 stickers on the neck photographs and tracheotomy trainers, to visually examine the accuracy of CTM identification. The rate of correct sticker placement in the neck photographs was 41.2% before the lecture, 80.7% 2 days after the lecture, and 77.3% 16 days after the lecture (before vs. 2 and 16 days after, p value < 0.01). For the tracheotomy trainer, the rate was 36.1% before the lecture, 97.5% 2 days after the lecture, and 94.1% 16 days after the lecture (before vs. 2 and 16 days after, p value < 0.01). Furthermore, the proportion of students with mistakes above and below the CTM was higher than that of students with mistakes to the right or left. In conclusion, the rate of accurate CTM identification among dental students was low before they underwent the relevant practicum, but most students were able to identify the CTM accurately after the lecture and practicum in a small class., Competing Interests: None declared.

What We Already Know About This Topic: WHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Success of a cricothyrotomy is dependent on accurate identification of the cricothyroid membrane. The objective of this study was to compare the accuracy of ultrasonography versus external palpation in localizing the cricothyroid membrane., Methods: In total, 223 subjects with abnormal neck anatomy who were scheduled for neck computed-tomography scan at University Health Network hospitals in Toronto, Canada, were randomized into two groups: external palpation and ultrasound. The localization points of the cricothyroid membrane determined by ultrasonography or external palpation were compared to the reference midpoint (computed-tomography point) of the cricothyroid membrane by a radiologist who was blinded to group allocation. Primary outcome was the accuracy in identification of the cricothyroid membrane, which was measured by digital ruler in millimeters from the computed-tomography point to the ultrasound point or external-palpation point. Success was defined as the proportion of accurate attempts within a 5-mm distance from the computed-tomography point to the ultrasound point or external-palpation point., Results: The percentage of accurate attempts was 10-fold greater in the ultrasound than external-palpation group (81% vs. 8%; 95% CI, 63.6 to 81.3%; P < 0.0001). The mean (SD) distance measured from the external-palpation to computed-tomography point was five-fold greater than the ultrasound to the computed-tomography point (16.6 ± 7.5 vs. 3.4 ± 3.3 mm; 95% CI, 11.67 to 14.70; P < 0.0001). Analysis demonstrated that the risk ratio of inaccurate localization of the cricothyroid membrane was 9.14-fold greater with the external palpation than with the ultrasound (P < 0.0001). There were no adverse events observed., Conclusions: In subjects with poorly defined neck landmarks, ultrasonography is more accurate than external palpation in localizing the cricothyroid membrane.

Accurate identification of the cricothyroid membrane (CTM) has paramount importance in the event of a 'cannot intubate, cannot oxygenate' scenario. We sought to determine the ability of anesthesiologists to correctly identify the CTM in obese and non-obese children. Anesthesiologists were asked to mark the entry point of the cricothyroidotomy device with an ultraviolet invisible pen on obese and non-obese (BMI < 95th percentile for age and sex) children aged 7-12 years. A correct estimation was defined as a mark made between the upper and lower borders of the CTM and within the 3-mm midline. Twenty anesthesiologists palpated 30 obese and 50 non-obese children. The CTM was accurately identified with digital palpation in a total 55% of children, and there were no differences inaccurate identification rates of the CTM between obese and non-obese children [57 vs. 54%, respectively; median difference 3%; 95% confidence interval (- 20 to 25%); p = 0.82]. Accuracy was not correlated with any demographic or morphometric features of the children. Percutaneous identification of the CTM in children aged 7-12 years was poor and not significantly different for obese and non-obese children. Pre-procedural ultrasonography may help to identify the landmarks for cricothyroidotomy.

Cricoid pressure is employed during rapid sequence induction to reduce the risk of pulmonary aspiration. Correct application of cricoid pressure depends on knowledge of neck anatomy and precise identification of surface landmarks. Inaccurate localisation of the cricoid cartilage during rapid sequence induction risks incomplete oesophageal occlusion, with potential for pulmonary aspiration of gastric contents. It may also compromise the laryngeal view for the anaesthetist. Accurate localisation of the cricoid cartilage therefore has relevance for the safe conduct of rapid sequence induction. We conducted a multicentre, prospective cohort study to determine the accuracy of cricoid cartilage identification in 100 patients. The cranio-caudal midpoint of the cricoid cartilage was identified by a qualified anaesthetic assistant using the conventional landmark technique and marked. While maintaining the patient in the same position, a second mark was made by identifying the midpoint of the cricoid cartilage using ultrasound scanning. The mean (SD) distance between the two marks was 2.07 (8.49) mm. In 41% of patients the midpoint was incorrectly identified by a margin greater than 5 mm. This error was uniformly distributed both above and below the midpoint of the cricoid cartilage. The Pearson correlation coefficient of this error with respect to body mass index was 0.062 (p = 0.539) and with age was -0.020 (p = 0.843). There were also no significant differences in error between male and female patients. Identification of cricoid position using a landmark technique has a high degree of variability and has little correlation with age, sex or body mass index. These findings have significant implications for the safe application of cricoid pressure in the context of rapid sequence induction., (© 2018 Association of Anaesthetists.)

Introduction: A surgical approach to airway management may be essential in situations of difficult or failed airway, where immediate airway access is needed to provide oxygenation. However, the procedure is uncommonly performed and expertise among emergency clinicians may be limited., Objectives: The aim of this study was to assess the accuracy of cricothyroid membrane (CTM) identification by junior and senior emergency trainees by identification of surface anatomy landmarks. A secondary aim was to determine patient variables associated with accurate identification of CTM., Methods: A prospective observational study was conducted in a tertiary emergency department in the Kingdom of Saudi Arabia. Saudi Emergency Medicine board trainees participated in the study. Data were also obtained on gender and body habitus of patients. Junior trainees attempted to locate the membrane by palpation and marked it with an ultraviolet mark (blinded) pen followed by senior trainees. A certified ultrasound physician, also blinded to the trainee attempts, marked the membrane within a 5 mm circumference using a different coloured ultraviolet pen and was used as the reference gold standard., Results: There were 80 patients enrolled with junior and senior doctors assessing location for emergency cricothyrotomy. Proportion of correct localisation was 30% (95% CI 20% to 41%) among junior trainees and 33% (95% CI 22% to 44%) among seniors (P=0.73). Level of training, sex, height and weight of patients were not associated with success., Conclusions: Clinical localisation of CTM by emergency medicine trainees was poor even in non-stressful settings, and warrants further dedicated education and/or use of adjunct techniques., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2018. No commercial re-use. See rights and permissions. Published by BMJ.)

Airway emergencies are life-threatening events that face providers of many different backgrounds. In cannot-intubate-cannot-ventilate situations, emergent access to the airway can be obtained through the cricothyroid membrane by cricothyroidotomy. The 3 main techniques are open, percutaneous, and needle cricothyroidotomy. To date, there is no compelling evidence demonstrating superiority of a particular approach. Ultimately, the method used for cricothyroidotomy should be based on the comfort and experience of the provider performing the procedure., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: Severely obese parturients have increased 'cannot intubate, cannot oxygenate' risk during Caesarean section under general anaesthesia. Front-of-neck access (FONA) at the cricothyroid membrane (CTM) is definitive management; however, attempted FONA can fail. Point-of-care ultrasonography may provide useful information about CTM depth to aid FONA in obesity. This study determined the difference in CTM depth between severely obese and non-obese parturients, utilising ultrasonography., Methods: In this prospective observational study, two anaesthetists performed airway ultrasonography on 15 severely obese (BMI >45 kg m -2 ) and 15 normal-weight (BMI ≤25 kg m -2 ) parturients in the third trimester, using the transverse and longitudinal planes, sniffing and extended head positions, and nil and firm transducer pressures. The primary outcome was CTM depth (millimetres) measured in the transverse plane with the head extended and nil transducer pressure. Secondary outcomes included CTM depth measurements using other factor configurations. Intra-class correlation coefficients assessed the inter-observer reliability., Results: CTM depth measured in the transverse plane with head extended and nil transducer pressure was significantly greater in severely obese parturients, mean 18.0 mm (95% confidence interval 16.3-19.8), vs 10.6 mm (8.81-12.4) in non-obese (P<0.001); mean difference 7.4 mm (4.9-9.9; P<0.001). CTM depths were increased in the severely obese group regardless of scanning plane, head and neck position, or transducer pressure (all P<0.001). There was excellent inter-observer reliability., Conclusions: Cricothyroid membrane depth is significantly increased in severely obese vs normal-weight parturients independently of scanning plane, head and neck position, or transducer pressure., (Copyright © 2018 British Journal of Anaesthesia. All rights reserved.)

Objectives: The aims of this study were to measure diameters of the cricoid ring and left main bronchus in Asian adult patients and to assess the accuracy of double lumen tube size selected according to cricoid and left main bronchus diameter, respectively., Design: Retrospective observational study., Setting: Academic, tertiary care hospital., Participants: Preoperative CT scans from 87 men and 94 women who had undergone general anesthesia for lung operations., Interventions: No intervention., Measurements and Main Results: The diameters of the cricoid ring and left main bronchus were measured from thoracic computed tomography images after correction of slant. The "best-fit" size of double lumen tube was determined by comparing diameter of the left main bronchus and cricoid ring with the diameter of the double lumen tube. Diameters of the cricoid ring and left main bronchus were both significantly greater in men compared with women (p < 0.0001). Shapes of cricoid rings were different between genders (p < 0.0001), while shapes of the left main bronchus were not significant different (p = 0.343). With reference to the "best fit" size, the rate of agreement of cricoid ring size, left main bronchus size, and height size for men were 100%, 100%, and 94.3%. For women, the rate of agreement of cricoid ring size, left main bronchus size, and height size were 94.7%, 63.8%, and 51.1%., Conclusions: The "best fit" size of a double lumen tube should be decided by a combination of diameters of the cricoid ring and the left main bronchus., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: There is disagreement regarding the anatomy of the pediatric airway, particularly regarding the shape of the cricoid cartilage and the location of the narrowest portion of the larynx., Aims: The aim of this review is to clarify the origin and the science behind these differing views., Methods: We undertook a review of published literature, University Libraries, and authoritative textbooks with key search words and phrases., Results: In vivo observations suggest that the narrowest portion of the airway is more proximal than the cricoid cartilage. However, in vitro studies of autopsy specimens measured with rods or calipers, confirm that the nondistensible and circular or near circular cricoid outlet is the narrowest level. These anatomic studies confirmed the classic "funnel" shape of the pediatric larynx. In vivo studies are potentially misleading as the aryepiglottic, vestibular, and true vocal folds are in constant motion with respiration. These studies also do not consider the effects of normal sleep, inhalation agents, and comorbidities such as adenoid or tonsil hypertrophy that cause some degree of pharyngeal collapse and alter the normal movement of the laryngeal tissues. Thus, the radiologic studies suggesting that the narrowest portion of the airway is not the cricoid cartilage may be the result of an artifact depending upon which phase of respiration was imaged., Conclusion: In vivo studies do not take into account the motion of the highly pliable laryngeal upper airway structures (aryepiglottic, vestibular, and vocal folds). Maximal abduction of these structures with tracheal tubes or bronchoscopes always demonstrates a larger opening of the glottis compared to the outlet of the cricoid ring. Injury to the larynx depends upon ease of tracheal tube or endoscope passage past the cricoid cartilage and not passage through the readily distensible more proximal structures. The infant larynx is funnel shaped with the narrowest portion the circular or near circular cricoid cartilage confirmed by multiple in vitro autopsy specimens carried out over the past century., (© 2017 John Wiley & Sons Ltd.)

Background: Landmark-guided internal jugular vein cannulation is difficult for pediatric patients but useful, especially when ultrasound equipment is unavailable. Therefore, it is important to define the adjacent anatomic characteristics of the pediatric internal jugular vein., Methods: In 210 children the course of the internal jugular vein, and common carotid and vertebral arteries was measured from the level of the cricoid cartilage to the supraclavicular area using ultrasound., Results: From the level of the cricoid cartilage to the supraclavicular area, vessel diameter increased with internal jugular vein increasing by 12%, and common carotid and vertebral arteries increasing by 5% each. From the level of the cricoid cartilage to the supraclavicular area, the number of patients with a medial common carotid artery position relative to the internal jugular vein increased, whereas those with a lateral position decreased; the number of patients with nonoverlapped common carotid artery-internal jugular vein increased, and those with totally overlapped decreased. In contrast, the overlapping status of vertebral artery-internal jugular vein changes oppositely. More than 97.14% of the vertebral artery lies lateral to the internal jugular vein at these levels. The minimal vertebral artery-internal jugular vein depth decreased from 0.46±0.20 to 0.37±0.19 cm. The angle from the internal jugular vein line to the horizontal line of the body was 83.35±9.04 degrees., Conclusion: The common carotid artery and internal jugular vein are farther apart as one moves down the neck, whereas the vertebral artery and internal jugular vein are getting together. Additionally, the diameter of the internal jugular vein increased., (© 2017 John Wiley & Sons Ltd.)

Emergency cricothyrotomy is a common feature in all difficult airway algorithms. It is the final step following a 'can't intubate, can't oxygenate' scenario. It is rarely performed and has a significant failure rate. There is variation in the reported size of the cricothyroid membrane, especially across population groups. Procedural failure may result from attempting to pass a device with too large an external diameter through the cricothyroid membrane. We aimed to determine the maximum height of the cricothyroid membrane in a UK trauma population. Electronic callipers were used to measure the maximum height of the cricothyroid membrane on 482 reformatted trauma computed tomography scans, 377 (78.2%) of which were in male patients. The mean (SD) height of the cricothyroid membrane, as independently measured by two radiologists, was 7.89 (2.21) mm and 7.88 (2.22) mm in male patients, and 6.00 (1.76) mm and 5.92 (1.71) mm in female patients. The presence of concurrent tracheal intubation or cervical spine immobilisation was found not to have a significant effect on cricothyroid membrane height. The cricothyroid membrane height in the study population was much smaller than that previously reported. Practitioners encountering patients who may require an emergency surgical airway should be aware of these data. Rescue airway equipment with variety of external diameters should be immediately available., (© 2017 The Association of Anaesthetists of Great Britain and Ireland.)

Background: Accurate location of the skin incision is helpful to decrease the technical difficulty and save the operative time in anterior cervical spine surgery. Spine surgeons usually use the traditional neck anatomic structures (the hyoid bone, thyroid cartilage, and cricoid cartilage) as landmarks during the surgery. However, the reliability of these landmarks has not been validated in actual practice., Objective: To find out which landmark is the most accurate for identifying the cervical levels in anterior cervical spine surgery., Methods: The lateral flexion and extension radiographs of cervical spine in standing position from 30 consecutive patients from January 2015 to February 2015 were obtained. The cervical vertebral bodies from C2 to C7 were divided equally into 2 segments. The cervical segments corresponding to each of the surface landmarks were recorded on the flexion and extension radiographs, respectively, and the displacement of corresponding cervical segments from the flexion to extension radiographs for each landmark was calculated., Results: Based on the measurements, the main corresponding cervical levels for the mandibular angle were C2 on both of the flexion and extension films, for the hyoid bone were the C3-C4 interspace on flexion film and C3 on extension film, for the thyroid cartilage C5 on both of flexion and extension films, and for the cricoid cartilage C6 on flexion film and C5-C6 interspace on extension film, respectively. The ratios of displacement within 2 segments from flexion to extension were 83.3% (25/30) for mandibular angle, 56.7% (17/30) for hyoid bone, 66.7% (20/30) for thyroid cartilage, and 56.7% (17/30) for cricoid cartilage, respectively. The mean displacement from flexion to extension films were significantly less than 2 cervical segments for the mandibular angle but greater than 2 segments for the other landmarks. Significant differences were found between mandibular angle and the other 3 landmarks for the displacement from flexion to extension., Conclusions: The angle of mandible was found to be the most accurate landmark for identifying the cervical level, which corresponded to C2 and C2-C3 disc space. The hyoid bone, thyroid cartilage, and cricoid cartilage were not reliable to predict the cervical levels., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Introduction: Computed tomography- (CT) and magnetic resonance imaging (MRI)-based measurements have recently suggested that the narrowest dimension of the pediatric airway is the subglottic region. These data are contrary to the previously held tenets of a funnel- or conical-shaped airway. The current study evaluates airway volumes and shapes using three-dimensional CT images of the air way column in spontaneously breathing children., Methods: The study included CT-based radiological images of the neck in children who required imaging unrelated to airway symptomatology. The children were evaluated during spontaneous ventilation during natural sleep or with sedation without airway devices in place. The three-dimensional images of the airway column were evaluated, volumes calculated, and comparisons made between the subglottic, cricoid, and tracheal volumes and shapes., Results: The study cohort included 54 children, ranging in age from 2 months to 8 years. An increase in the airway volumes was observed from the subglottic (0.17 ± 0.06 mm 3 ) to the cricoid (0.19 ± 0.06 mm 3 ) to the tracheal regions (0.22 ± 0.07 mm 3 ). The volumes of the subglottic, cricoid, and tracheal regions demonstrated a linear relationship with age., Conclusion: This study confirms recent studies demonstrating that the subglottic region not the cricoid is the narrowest part of the airway., (© 2017 John Wiley & Sons Ltd.)

Background: Recent studies suggest that the pediatric airway is elliptical with the subglottis rather than the cricoid as the narrowest part contrary to the old belief of a funnel-shaped airway. The shape of the airway in neonates and infants has not been studied separately. This study seeks to define the shape of the upper airway in neonates and infants, and determine if there are differences in airway shape between infants and older children., Methods: We studied 40 computed tomographic scans of children from birth to 12 months of age undergoing radiological evaluation unrelated to airway symptomatology. The computed tomographic scans were obtained during either natural sleep or with sedation and spontaneous ventilation without airway devices in place. Transverse and anteroposterior diameters were measured at the subglottic level and at the cricoid ring., Results: The mean age was 5.9 ± 3.4 months. The mean transverse and anteroposterior diameters were 5.3 ± 0.83 mm and 7.2 ± 0.89 mm at the subglottic region and 6.1 ± 0.86 mm and 6.7 ± 0.79 mm at the cricoid level. An increase in the transverse dimension of the airway was observed from the subglottic region to the cricoid ring. Although the anteroposterior dimension decreased from the subglottis to the cricoid ring, the airway remained wider in the anteroposterior dimension compared to the transverse dimension from the subglottis to the cricoid ring., Conclusion: The present study demonstrates that the airway in neonates and infants between the subglottic area and the cricoid remains elliptical. The cricoid is not round as has been observed in older children. The airway is wider anteroposteriorly and narrows in the transverse dimension from the subglottis to the cricoid in infants., (© 2017 John Wiley & Sons Ltd.)

Background: We tested the hypothesis whether gender differences exist in the applied cricoid force necessary to prevent regurgitation. Real-time visual and dynamic means were used to assess the effectiveness of different applied cricoid forces in occluding the esophageal entrance in men (group 1) and in women (group 2)., Methods: In anesthetized and paralyzed patients, the glottis and esophageal entrance were visualized with a Glidescope video laryngoscope. Trained operators performed cricoid pressure (CP) and gastric tube insertion trials. Successful gastric tube insertion in the presence of CP was considered ineffective CP, whereas unsuccessful insertion was considered effective CP. The applied cricoid forces were measured with a novel instrument, the cricometer. The first patient in each group received 20 N. The applied cricoid force in successive patients was determined by the response of the previous patient within the same group, using the up-and-down sequential allocation technique., Results: In the 30 men and 30 women who qualified for the study, the median cricoid force (cricoid force = 50) that occluded the esophageal entrance was 30.8 N (95% confidence interval = 28.15-33.5) in men, and 18.7 N in women (95% confidence interval = 17.1-20.3; P < .0001). Patency of the esophageal entrance was observed when CP was not applied and when inadequate forces that allowed successful esophageal cannulation were used., Conclusions: The current study provides evidence that the median force necessary to occlude the esophageal entrance to prevent regurgitation is less in women compared with men. Applying the appropriate cricoid force in women should also decrease airway-related problems that tend to occur with the use of excessive forces. The findings of the current study may only be applicable to patients with normal body habitus.

We experienced difficulty inserting cuffed inner diameter (ID) 4.5- and 5.0-mm endotracheal tubes (ETTs) in a 5-year-old boy. Postoperative ultrasound investigations showed that the internal transverse width of the cricoid cartilage was 8.0 mm. The maximum outer diameter (OD) of the deflated cuff portion of the cuffed ID 4.5- and 5.0-mm ETTs was 8.5 and 9.6 mm, respectively. The OD of an uncuffed ID 5.5-mm ETT was 7.6 mm; this tube passed the cricoid cartilage. Hence, the transverse width of the cricoid cartilage and ETT diameter including cuff folds should be considered when selecting cuffed ETTs.

Endotracheal tube (ETT) should be placed at the optimal level to avoid single lung ventilation or accidental extubation. This study was performed to estimate the mid-tracheal level by using surface anatomical landmarks in adult patients.Neck computed tomography images of 329 adult patients between the ages of 16 and 79 years were reviewed. In the midline sagittal plane, the levels corresponding to the vocal cords, cricoid cartilage, suprasternal notch, manubriosternal junction, and carina were identified. The surface distances from the cricoid cartilage to the suprasternal notch (extCC-SSN) and that from the suprasternal notch to the manubriosternal junction (extSSN-MSJ) were measured. The relationship between mid-tracheal level and the surface distances was analyzed using Bland-Altman plot.The difference between the extCC-SSN and the mid-tracheal level was -6.6 (12.5) mm, and the difference between the extSSN-MSJ and the mid-tracheal level was -19.2 (6.1) mm. The difference between the extCC-SSN and the mid-tracheal level was smaller in females compared with males [-1.7 (11.7) mm vs -12.8 (10.7) mm; P < 0.001].The mid-tracheal level, which is helpful in planning the insertion depth of an ETT, can be predicted by the surface distance between the cricoid cartilage and suprasternal notch in adults, especially in females.

Objectives: Sonography has been suggested as a possible means of endotracheal tube (ETT) placement confirmation. However, optimum ultrasound transducer placement has not been established. Using a cadaveric model, ETT placement by the sonographic appearance at the thyroid cartilage, cricoid cartilage, and suprasternal notch in the upper airway was assessed to determine which ultrasound transducer placement offered the most optimal images for ETT confirmation in the airway., Methods: One provider intubated 5 cadavers, with the ultrasound transducer at each of the 3 levels, for a total of 30 intubations per specimen, while 2 providers assigned a visual score of 1 (subtle), 2 (clear), or 3 (pronounced) to each sonogram of the ETT in the airway., Results: At the level of the thyroid cartilage, tracheal intubation was detected at a rate of 40%, with a median visualization scale of 1 (subtle movement). At the level of the cricoid cartilage, the visualization scale improved to a median of 2 (clear movement), with a 70% intubation detection rate. At the level of the suprasternal notch, 100% of the tracheal intubations were visualized on sonography, with a median score of 3 (pronounced movement)., Conclusions: In comparing sonographic detection of ETT placement at 3 levels of the upper airway in a cadaveric model, our results clearly indicate that visualization was superior at the level of the suprasternal notch, with 100% of intubations detected with the best visualization scores., (© 2017 by the American Institute of Ultrasound in Medicine.)

Background: Optimal positioning of endotracheal tubes (ETTs) decreases the risk of accidental extubation or endobronchial intubation. This study evaluated the usefulness of external anatomical landmarks as practical references for determining an insertion depth of an ETT in pediatric patients., Methods: Computed tomography images of the necks of 183 pediatric patients (≤16 years of age) were reviewed. Levels corresponding to the vocal cords, cricoid cartilage, suprasternal notch, manubriosternal junction, and carina were identified on sagittal reconstructed images. The surface measurements from the cricoid cartilage to the suprasternal notch and that from the suprasternal notch to the manubriosternal junction were determined. Bland-Altman analysis was used to interpret the relationship between the midtracheal level and the surface measurements., Results: The difference between the midtracheal level and the surface distance from the cricoid cartilage to the suprasternal notch was 3.5 ± 7.0 mm, which was closer to zero than that between the midtracheal level and the surface distance from the suprasternal notch to the manubriosternal junction of 15.1 ± 6.1 mm., Conclusion: The midtracheal level, helpful in planning the insertion depth of an ETT, can be predicted by measuring the surface distance from the cricoid cartilage to suprasternal notch in pediatric patients., (© 2016 John Wiley & Sons Ltd.)

Purpose: Anatomic variations complicate surface landmark-guided needle placement, thereby increasing nerve blockade failure rate. However, little is understood about how anatomic distances change under different clinical conditions. As the cricoid cartilage is an easy and accurate landmark, we investigated changes in distance between the sixth or seventh cervical transverse processes (C6TP or C7TP) and the cricoid cartilage in neutral and extended supine positions., Methods: Forty-two patients (16 men, 26 women) were included in this study. Distances between the cricoid cartilage and C6TP/C7TP were measured using ultrasonography with the patient in neutral and extended supine positions., Results: C6TP and C7TP were caudally located at 6.0 ± 8.1 and 15.1 ± 7.2 mm, respectively, from the cricoid cartilage in the neutral supine position, and at 15.2 ± 8.0 and 25.3 ± 8.0 mm, respectively, in the extended supine position. In the extended supine position, the cricoid cartilage was more cephalad than C6TP and C7TP in all patients. The distance from the cricoid cartilage to C6TP was 12.1 ± 7.6 mm in men and 17.2 ± 7.7 mm in women., Conclusion: C6TP and C7TP are located approximately 15 and 25 mm, respectively, caudal to the cricoid cartilage in the extended supine position. Our results highlight the fact that there can be significant anatomic variation between the extended and neutral supine positions used in stellate ganglion block, which should be kept in mind when devising easily identifiable and palpable surface landmarks., Competing Interests: No external funding and no competing interests declared.

We encountered difficulty in inserting a 32-Fr left double-lumen tube (DLT) in a small 75-year-old Japanese woman (height, 144 cm). The 32-Fr DLT with 10.1 × 11.2-mm tracheal diameter could not pass through the cricoid cartilage with a 9.2-mm transverse inner width. The transverse inner width of the cricoid cartilage, in addition to the tracheal and bronchial diameter, can be measured using computed tomography or ultrasonography in small women. Thus, a 28-Fr DLT or single-lumen tube and a blocker can be selected instead of a 32-Fr DLT when the width of the cricoid cartilage is <10 mm.

Objective: The present study aimed to clarify individual variations in the cricothyroid joint (CT joint)., Methods: Using 30 specimens of the CT joint obtained from elderly donated cadavers, we examined the composite fibers of the capsular ligament as well as the morphology of the synovial tissue., Results: The capsular ligament consistently contained abundant thick elastic fiber bundles on the anterior side of the joint (anterior band) and an elastic fiber-made mesh on the posterior side (posterior mesh). The synovial membrane, lined by synovial macrophages, was usually restricted to the recesses in the medial or inferior end of the joint cavity. Without the synovial lining, elastic fibers of the capsular ligament were subsequently detached, dispersed, and exposed to the joint cavity. We also observed a folded and thickened synovial membrane and a hypertrophic protrusion of the capsular ligament. In six specimens, the joint cavity was obliterated by debris of synovial folds and elastic fiber-rich tissues continuous with the usual capsular ligament. Notably, with the exception of two specimens, we did not find lymphocyte infiltration in the degenerative synovial tissue., Discussion: We considered the CT joint degeneration to be a specific, silent form of osteoarthritis from the absence of lymphocyte infiltration. For high-pitched phonation, the elderly CT joint seemed to maintain its anterior gliding and rotation with the aid of elastic fiber-rich tissues compensating for the loss of congruity between the joint cartilage surfaces. Conversely, however, high-pitched phonation may accelerate obliteration of the joint., (Copyright © 2016 The Voice Foundation. Published by Elsevier Inc. All rights reserved.)