ORIGINAL ARTICLE: Accuracy of surface landmark identification for cannula cricothyroidotomy

Palpation Versus Ultrasonography for Identifying the Cricothyroid Membrane in Case of a Laterally Deviated Larynx: A Randomized Trial

BACKGROUND

Large neck circumference and displacement of the trachea due to pathology increase the risk of failed identification of the cricothyroid membrane and cricothyroidotomy. We investigated whether ultrasound aids in the successful identification of the cricothyroid membrane in a model of an obese neck with midline deviation of the trachea.

METHODS

We developed silicone neck models that were suitable for both palpation and ultrasonography and where the trachea deviated laterally from the midline to either side. After reading a book chapter and participating in a 25-minute lecture and a 15- to 23-minute hands-on demonstration and rehearsal of ultrasonography for identification of the cricothyroid membrane, anesthesiologists and anesthesiology residents randomly performed identification with either ultrasound or palpation on 1 of 2 neck models.

RESULTS

We included 57 participants, of whom 29 and 28 were randomized to palpation and ultrasound, respectively. Correct identification of the cricothyroid membrane was achieved by 21 (75.0%) vs 1 (3.5%) of participants in the ultrasound versus palpation groups (risk ratio [RR], 21.8 [95% confidence interval {CI}, 3.1-151.0]). The tracheal midline position in the sagittal plane was identified correctly by 24 (85.7%) vs 16 (55.2%) of participants in the ultrasound versus palpation groups (RR, 1.6 [95% CI, 1.1-2.2]).

CONCLUSIONS

Identification of the cricothyroid membrane in a model of an obese neck with midline deviation of the trachea was more often successful with ultrasound compared to palpation. Our study supports the potential use of ultrasound before induction of anesthesia and airway management in this group of patients, and it may even be applied in emergency situations when ultrasound is readily available. Further studies in human subjects should be conducted.

Role of point-of-care ultrasound in critical care and emergency medicine: update and future perspective

Point-of-care ultrasound (POCUS) is a rapidly developing technology that has the potential to revolutionize emergency and critical care medicine. The use of POCUS can improve patient care by providing real-time clinical information. However, appropriate usage and proper training are crucial to ensure patient safety and reliability. This article discusses the various applications of POCUS in emergency and critical care medicine, the importance of training and education, and the future of POCUS in medicine.

Training Requirements in Point-of-Care Ultrasonography of the Upper Airway: A Feasibility Study

OBJECTIVES

Point-of-care ultrasonography of the upper airway can be a useful supplement to conventional pre-anesthetic clinical evaluations. However, the reliability of such examinations is highly operator-dependent and proper training in sonoanatomy and ultrasound operational skills are required. The objective of this study aims to assess the minimum training requirements for applying a predefined upper airway scanning protocol in healthy volunteers by anesthesia trainees.

METHODS

Twenty-two healthy volunteer members of the Operating Room staff participated in the study. A predefined scanning protocol that included the identification of specific structures (hyoid bone, vocal cords, thyrohyoid membrane/epiglottis/pre-epiglottic space, cricothyroid membrane, and thyroid gland), as well as the performance of specific measurements (distance from the hyoid bone to skin, anterior commissure to skin, epiglottis to skin, and thyroid isthmus to skin) was taught in a single-day training course. The trainees' competence was assessed after multiple scanning repetitions performed over a week. Mixed effects regression models were applied for the trainee-instructor differences in all ultrasound measurements.

RESULTS

Cricothyroid membrane visualization had the lowest success rate (88%). Trainee-instructor differences were statistically significant for hyoid bone-to-skin (P < .001) and epiglottis-to-skin distances (P = .016). Measurement of the distance from the epiglottis to the skin required more scanning repetitions to achieve minimum deviance compared with other measurements. Ten or fewer scanning repetitions were sufficient to achieve minimum deviance for all four measurements.

CONCLUSIONS

At least 10 scanning repetitions of a pre-defined upper airway scanning protocol can be used as the minimum standard for training.

A Scoping Review of Ultrasonographic Techniques in the Evaluation of the Pediatric Airway

Point-of-care ultrasound is making rapid advancements in pediatrics, and ultrasonographic assessment of the airway is being employed in many specialties such as the pediatric, cardiac, and neonatal intensive care units, emergency department, pulmonary clinic, and the perioperative setting. This scoping review provides a technical description of image acquisition and interpretation, accompanying ultrasound images of the hallmark airway applications in pediatrics, and supporting evidence when available. We describe and illustrate ultrasound-determined endotracheal tube (ETT) sizing, ETT placement and depth confirmation, vocal fold assessment, prediction of post-extubation stridor, difficult laryngoscopy prediction, and cricothyrotomy guidance. This review aims to provide the descriptions and images necessary to learn and apply these skills at the point of care in the pediatric patient.

Equivalence of the top-down manoeuvre and bottom-up manoeuvre in speed and accuracy of identifying the cricothyroid membrane: a prospective randomised cross-over study

BACKGROUND

Accurate identification of the cricothyroid membrane is crucial for successful cricothyrotomy; however, a manoeuvre that helps identify it both accurately and quickly remains unclear. The effectiveness of the so-called 'bottom-up manoeuvre' has never been investigated. This study aimed to examine whether the bottom-up manoeuvre is as rapid and accurate as the conventional 'top-down manoeuvre' at identifying the cricothyroid membrane.

METHODS

This study was a prospective randomised cross-over trial conducted at an academic medical centre between 2018 and 2019. Fifth-year medical students participated. The students were trained in the use of either the top-down manoeuvre or the bottom-up manoeuvre first. Each student subsequently performed the technique once on a volunteer. The students were then taught and practiced the other manoeuvre as well. The accuracy of cricothyroid membrane identification and the time taken by successful participants only were measured and compared between the manoeuvres using equivalence tests with two one-sided tests.

RESULTS

A total of 102 medical students participated in this study and there was no missing data. The accuracy of identification and time required for success were similar between the top-down manoeuvre and the bottom-up manoeuvre (65.7% vs. 70.6%, taking 13.8 s [interquartile range (IQR): 9.4-17.5] vs. 15.5 s [IQR: 11.5-19.9], respectively). The success rate was statistically equivalent (rate difference, 4.9%; 90% confidence interval [CI], -5.8 to 15.6; equivalence margin, -20.0 to 20.0). The time required for success was also statistically equivalent (median difference, 1.7 s; 90% CI, -0.2 to 3.3; equivalence margin, -4.0 to 4.0).

CONCLUSION

Among students first trained in both manoeuvres for identifying the cricothyroid membrane, the speed and accuracy of identification were similar between those using the bottom-up manoeuvre and those using the top-down manoeuvre.

Association between Successful Palpation of the Cricothyroid Membrane and the 3-3-2 Rule for Predicting Difficult Airway in Female Patients Undergoing Non-Neck Surgery: A Prospective Observational Cohort Study

Background: Prediction of difficult airway is important for airway management in patients undergoing surgery. The assessment of airway structures and establishment of protective airway strategies are essential to improve patient safety. However, the association between successful palpation of the cricothyroid membrane and airway predictions has not been fully elucidated in patients undergoing surgery. We investigated this in female patients undergoing non-neck surgery. Methods: A total of 68 female patients were enrolled in this prospective observational cohort study between January 2021 and June 2021 at Eunpyeong St. Mary’s Hospital, College of Medicine, Catholic University of Korea, Seoul, Republic of Korea. Exclusion criteria were male patients and those with neck pathology or neck surgery. The assessment of difficult airway was performed before the induction of anesthesia and was defined by one of the following conditions: inter-incisor distance < 3 fingerbreadths, hyoid-to-mental distance < 3 fingerbreadths, and thyroid-to-hyoid distance < 2 fingerbreadths (the “3-3-2 rule”). The accuracy of palpable identification of the cricothyroid membrane was confirmed by ultrasonography (US). The patients were divided into the non-difficult airway (NDA) group (n = 30) and the difficult airway (DA) group (n = 30). Results: The two groups were comparable in terms of age, but the DA group had higher body mass index (BMI). In airway assessment, 9 patients showed inter-incisor distance < 3 fingerbreadths, 3 patients showed hyoid-to-mental distance < 3 fingerbreadths, and 24 patients showed thyroid-to-hyoid distance < 2 fingerbreadths in the DA group. The rate of successful palpation of the cricothyroid membrane was higher in the patients without than in those with difficult airway variables. Conclusions: Patients with a positive 3-3-2 rule showed a poor palpability of cricothyroid membrane.

Comparison of the Conventional Downward and Modified Upward Laryngeal Handshake Techniques to Identify the Cricothyroid Membrane: A Randomized, Comparative Study

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.

Accuracy of cricothyroid membrane identification using ultrasound and palpation techniques in obese obstetric patients: an observational study

BACKGROUND

During performance of emergency front of neck access, the final step in management algorithms for the 'can't intubate, can't oxygenate' scenario, accurate identification of the cricothyroid membrane, is crucial. Accurate identification using palpation techniques is low, with highest failure rates occurring in obese females.

METHODS

This prospective observational study recruited 28 obese obstetric patients. The cricothyroid membrane was identified using ultrasound, marked with an ultraviolet pen and covered with a dressing. The candidate was asked to perform cricothyroid membrane identification using landmark technique (group L) followed by ultrasound (group U). The primary outcome was the distance between the actual and estimated cricothyroid membrane midpoint. Secondary outcomes were the proportion of accurate assessments, time taken, and subjective ease of identification using a visual analogue score.

RESULTS

Distance from the cricothyroid membrane midpoint was shorter in group U than Group L (2.5 mm vs 5.5 mm, P=0.002). The proportion of correctly identified cricothyroid membranes was greater in group U than group L (71% vs 39%, P=0.015). Time required for identification was shorter in group L than group U (16.9 s vs 23.5 s, P=0.001). Visual analogue scores for ease of identification were lower in group U than group L (2.4 cm vs 4.2 cm, P=0.013).

CONCLUSIONS

Ultrasound-guided cricothyroid membrane localisation was significantly more accurate but slower than the landmark technique in obese obstetric patients. As such, we recommend the use of pre-procedural identification of the cricothyroid membrane in this patient population and formal training of anaesthetists in airway ultrasound.

Simulation of Adult Surgical Cricothyrotomy for Anesthesiology and Emergency Medicine Residents: Adapted for COVID-19

INTRODUCTION

In a CICO (cannot intubate, cannot oxygenate) situation, anesthesiologists and acute care physicians must be able to perform an emergency surgical cricothyrotomy (front-of-neck airway procedure). CICOs are high-acuity situations with rare opportunities for safe practice. In COVID-19 airway management guidelines, bougie-assisted surgical cricothyrotomy is the recommended emergency strategy for CICO situations.

METHODS

We designed a 4-hour procedural simulation workshop on surgical cricothyrotomy to train 16 medical residents. We provided prerequisite readings, a lecture, and a videotaped demonstration. Two clinical scenarios introduced deliberate practice on partial-task neck simulators and fresh human cadavers. We segmented an evidence-based procedure and asked participants to verbalize the five steps of the procedure on multiple occasions.

RESULTS

Thirty-two residents who participated in the workshops were surveyed, with a 97% response rate (16 of 16 from anesthesiology, 15 of 16 from emergency medicine). Participants commented positively on the workshop's authenticity, its structure, the quality of the feedback provided, and its perceived impact on improving skills in surgical cricothyrotomy. We analyzed narrative comments related to three domains: preparation for the procedure, performing the procedure, and maintaining the skills. Participants highlighted the importance of performing the procedure many times and mentioned the representativeness of fresh cadavers.

DISCUSSION

We developed a surgical cricothyrotomy simulation workshop for anesthesiology and emergency medicine residents. Residents in the two specialities uniformly appreciated its format and content. We identified common pitfalls when executing the procedure and provided practical tips and material to facilitate implementation, in particular to face the COVID-19 pandemic.

Ultrasonography for airway management

Ultrasonography (USG) allows a new approach to the airway in anaesthesia and intensive care. USG visualises the airway from the mouth to the lungs. By exploring the entire airway, USG proposes new criteria (1) to assess the risk of difficult laryngoscopy, (2) to anticipate the management of a difficult airway, (3) to confirm the position of the endotracheal tube (ETT), and (4) to confirm that the lungs are effectively ventilated. Intraoperatively, USG may also help to resolve acute ventilatory problems such as pneumothorax, delayed selective bronchial intubation after patient positioning (Trendelenburg, prone or lateral position) or acute pulmonary oedema.

Quantification of the effect of body mass index on cricothyroid membrane depth: a cross-sectional analysis of clinical CT images

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/m³) (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/m² to 16.8 (95% CI 13.7 to 20.1) at BMI 40 kg/m².

CONCLUSION

CTM depth was strongly associated with BMI in a retrospective analysis of patients having clinical CT scans.

The effect of patient positioning on ultrasound landmarking for cricothyrotomy

PURPOSE

Our primary objective was to assess the difference in position of the ultrasound-guided landmark of the cricothyroid membrane (CTM) when performed with the supine patient positioned at different head of bed (HOB) elevations.

METHODS

In this prospective observational study of patients presenting to the emergency department with non-life-threatening complaints, subjects underwent ultrasound-guided landmarking of the CTM with HOB elevation at 0°, 30°, and 90°. A linear mixed effects regression model was used to assess the change in the CTM landmark associated with head position. We used a second adjusted linear mixed effects model to assess possible confounding patient factors associated with these changes.

RESULTS

One-hundred and ten patients were enrolled, with a median [interquartile range] age of 39 [29-59] yr and 51:49 female:male ratio. Head of bed elevation at 30° and 90° resulted in a cephalad change in the CTM landmark of 2.7 mm (99% confidence interval [CI], 1.7 to 3.8; P < 0.001) and 4.2 mm (99% CI, 3.2 to 5.3; P < 0.001) respectively compared with the landmark at 0°. Body mass index (BMI) was associated with a change of 4.6 mm (99% CI, 0.5 to 8.7; P = 0.004) for BMI ≥ 30 compared with < 18.5 kg·m^-2 The impact of patient age on distance depended on HOB elevation, where patients > 70 yr had a change of 2.6 mm (99% CI, 0.01 to 5.1; P = 0.009) at 90° HOB elevation compared with 30°.

CONCLUSION

The location of the ultrasound-identified surface landmark of the CTM moves in a cephalad direction by changing the position of the HOB from supine 0° to elevation at 30° and 90°. This may be clinically important when attempting cricothyrotomy using a percutaneous (blind) technique, particularly when CTM identification and cricothyrotomy are performed at different head elevations.

The role of ultrasound in front-of-neck access for cricothyroid membrane identification: A systematic review

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.

Comparison of surgical cricothyroidotomy training: a randomized controlled trial of a swine model versus an animated robotic manikin model

Background

Airway obstruction remains a preventable cause of death on the battlefield. Surgical cricothyroidotomy is an essential skill for immediate airway management in trauma. Training for surgical cricothyroidotomy has been undertaken using simulators, cadavers or animal models. The ideal approach to training for this low volume and high-risk procedure is unknown. We hypothesized that current simulation technology provides an equal or better education for surgical cricothyroidotomy when compared with animal tissue training.

Methods

We performed a prospective randomized controlled study comparing training for surgical cricothyroidotomy using hands-on training on swine versus inanimate manikin. We enrolled medical students who had never performed or had formal instruction on surgical cricothyroidotomy. We randomized their instruction to use either a swine model or the inanimate version of the Operative Experience Inc. advanced surgical manikin. Participants' skills were then evaluated on human cadavers and on an advanced robotic manikin. Tests were scored using checklists modified from Objective Structured Assessment of Technical Skills and Tactical Combat Casualty Care. We compared scores between the groups using Wilcoxon rank sum tests and generalized linear models.

Results

Forty-eight participants were enrolled and trained; 30 participants completed the first testing session; 25 completed the second testing session. The mean time to establish an airway from the incision until the cuff was blown up was 95±52 s. There were no significant differences in any of the outcome measures between the two training groups.

Discussion

Measured performance was not different between subjects trained to perform surgical cricothyroidotomy on an animal model or a high fidelity manikin. The use of an advanced simulator has the potential to replace live tissue for this procedure mitigating concerns over animal rights.

Levels of evidence

I.

Supraglottic jet oxygenation and ventilation - A novel ventilation technique

Supraglottic jet oxygenation and ventilation (SJOV) is a novel minimally invasive supraglottic technique of jet ventilation which has shown superior results in maintaining oxygenation without any major complications. Theoretically, it could maintain PaO₂ and PaCO₂ within physiological limits for as long as required, the maximum duration reported till now is 45 min. The distinct advantage of SJOV over techniques of nasal oxygenation is its ability to record EtCO₂ during the periods of ventilation. In addition, it also provides reliable airway access by the blind passage of the endotracheal tube into the trachea with a high success rate even in Cormack-Lehane-III (CLIII) grading patients. Potential complications seen with SJOV include nasal bleed and sore throat. No studies have shown to cause severe barotrauma. In this article, we review the evidence regarding oxygenation, ventilation, indications, airway patency and complications of SJOV in comparison to other more commonly used supraglottic oxygenation and ventilation devices.

Ultrasound for airway management: An evidence-based review for the emergency clinician

BACKGROUND

Airway management is a common procedure performed in the Emergency Department with significant potential for complications. Many of the traditional physical examination maneuvers have limitations in the assessment and management of difficult airways. Point-of-care ultrasound (POCUS) has been increasingly studied for the evaluation and management of the airway in a variety of settings.

OBJECTIVE

This article summarizes the current literature on POCUS for airway assessment, intubation confirmation, endotracheal tube (ETT) depth assessment, and performing cricothyroidotomy with an emphasis on those components most relevant for the Emergency Medicine clinician.

DISCUSSION

POCUS can be a useful tool for identifying difficult airways by measuring the distance from the skin to the thyrohyoid membrane, hyoid bone, or epiglottis. It can also predict ETT size better than age-based formulae. POCUS is highly accurate for confirming ETT placement in adult and pediatric patients. The typical approach involves transtracheal visualization but can also include lung sliding and diaphragmatic elevation. ETT depth can be assessed by visualizing the ETT cuff in the trachea, as well as using lung sliding and the lung pulse sign. Finally, POCUS can identify the cricothyroid membrane more quickly and accurately than the landmark-based approach.

CONCLUSION

Airway management is a core skill in the Emergency Department. POCUS can be a valuable tool with applications ranging from airway assessment to dynamic cricothyroidotomy. This paper summarizes the key literature on POCUS for airway management.

Preparation for and Management of “Failed” Laryngoscopy and/or Intubation

An airway manager’s primary objective is to provide a path to oxygenation. This can be achieved by means of a facemask, a supraglottic airway, or a tracheal tube. If one method fails, an alternative approach may avert hypoxia. We cannot always predict the difficulties with each of the methods, but these difficulties may be overcome by an alternative technique. Each unsuccessful attempt to maintain oxygenation is time lost and may incrementally increase the risk of hypoxia, trauma, and airway obstruction necessitating a surgical airway. We should strive to optimize each effort. Differentiation between failed laryngoscopy and failed intubation is important because the solutions differ. Failed facemask ventilation may be easily managed with an supraglottic airway or alternatively tracheal intubation. When alveolar ventilation cannot be achieved by facemask, supraglottic airway, or tracheal intubation, every anesthesiologist should be prepared to perform an emergency surgical airway to avert disaster.

Apprasial of the surface anatomy of the Thorax in an adolescent population

Surface anatomy is considered a fundamental part of anatomy curricula and clinical practice. Recent studies have reappraised surface anatomy using CT, but the adolescent age group has yet to be appraised. Sixty adolescent thoracoabdominal CT scans (aged 12-18 years) were examined. The surface anatomy of the central veins, cardiac apex, diaphragmatic openings, and structures in relation to the sternal angle plane were analyzed. The results showed that the brachiocephalic vein (left and right) formed mostly posterior to the sternoclavicular joint. The superior vena cava formed close to the second costal cartilage, ±16.3 mm to the right of the midline. The apex of the heart was located in relation to the fifth intercostal space; ±78.6 mm to the left of the midline. The caval hiatus was in relation to T9 and T10; the esophageal hiatus was at T10; whereas the aortic hiatus was at T11. The sternal angle plane was in relation to the upper half of T5, which was also where the bifurcations of the trachea and pulmonary trunk were observed. The SVC/azygos vein junction and the concavity of the aortic arch were observed to be more than 10 mm superior to this plane. The results of this study further highlight the substantial variability of the surface anatomy between age groups. It also emphasizes the notion that surface anatomy is a dynamic variable and cannot be treated as a static observation. Clin. Anat. 32:762-769, 2019. © 2019 Wiley Periodicals, Inc.

Locating the cricothyroid membrane in males: Influence of the morphological characteristics of the neck

INTRODUCTION

Cricothyrotomy is a recommended technique to restore oxygenation in most of guidelines for difficult airway management. A correct location of the cricothyroid membrane (CTM) is fundamental for a proper performance of the technique. Several studies have shown poor accuracy with the identification the CTM by palpation, resulting in a high failure rate of the technique.

OBJECTIVE

The aim of this study was to determine the impact of the patient's neck morphology on the accurate location of the CTM and on the time employed.

MATERIALS AND METHOD

Observational study in which anaesthesiologists and intensivists voluntarily participated in a simulation that consisted of a «cannot intubate, cannot oxygenate» scenario, where they had to locate the CTM, as soon as possible, in 2 selected male patients with different morphological characteristics of the neck. The time was measured from the beginning of CTM palpation to locating it with a marker.

RESULTS AND CONCLUSIONS

A higher body mass index and a higher neck circumference correlated with a 70% location failure rate and with a longer time as compared with a standard model.

Ultrasound Is Superior to Palpation in Identifying the Cricothyroid Membrane in Subjects with Poorly Defined Neck Landmarks

Editor’s Perspective

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 &lt; 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 &lt; 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 &lt; 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.

The Use of Point-of-Care Ultrasonography in Trauma Anesthesia

Caring for the trauma patient requires an in-depth knowledge of the pathophysiology of trauma, the ability to rapidly diagnose and intervene to reverse the derangements caused by shock states, and an aptitude for the use of advanced monitoring techniques and perioperative point-of-care ultrasonography (P-POCUS) to assist in diagnosis and delivery of care. Historically, anesthesiology has lagged behind in wholly embracing this technology. P-POCUS has the potential to allow the trauma anesthesiologist to diagnose numerous injuries, quickly guide the placement of central vascular catheters and invasive monitors, and assess the efficacy of interventions.

Point-of-Care Airway Ultrasonography Prior to an Emergency Cricothyroidotomy: Case Report

The use of ultrasonography in acute and critical care medicine is becoming increasingly common. However, use of an airway ultrasound as an adjunct to determine the type of intervention needed and assess complications is not common practice. We report a 56-year-old male who presented to the Emergency Department of the Sungai Buloh Hospital, Selangor, Malaysia, in 2015 with hoarseness, stridor and impending respiratory failure. A point-of-care ultrasound performed to assess the neck and vocal cords indicated a heterogeneous echogenic mass in the larynx, thus ruling out a cricothyroidotomy. The patient was therefore referred for an emergency tracheostomy. This case highlights the importance of point-of-care airway ultrasonography in the assessment of patients with stridor. This imaging technique not only helps to detect the cause of the stridor, but also to determine the feasibility of a cricothyroidotomy in emergency cases.

[Ultrasound guided airway access]

Ultrasound has increasingly growing applications in anesthesia. This procedure has proven to be a novel, non-invasive and simple technique for the upper airway management, proving to be a useful tool, not only in the operating room but also in the intensive care unit and emergency department. Indeed, over the years mounting evidence has showed an increasing role of ultrasound in airway management. In this review, the authors will discuss the importance of ultrasound in the airway preoperative assessment as a way of detecting signs of difficult intubation or to define the type and/or size of the endotracheal tube as well as to help airway procedures such as endotracheal intubation, cricothyrotomy, percutaneous tracheal intubation, retrograde intubation as well as the criteria for extubation.

Morphological Characterization of Diaphragm in Common Squirrel Monkey (Saimiri sciureus)

The wall of the diaphragm can be affected by congenital or acquired alterations which allow the passage of viscera between the abdominal and chest cavities, allowing the formation of a diaphragmatic hernia. We characterized morphology and performed biometrics of the diaphragm in the common squirrel monkey Saimiri sciureus. After fixation, muscle fragments were collected and processed for optical microscopy. In this species the diaphragm muscle is attached to the lung by phrenopericardial ligament. It is also connected to the liver via the coronary and falciform ligaments. The muscle is composed of three segments in total: 1) sternal; 2) costal, and 3) a segment consisting of right and left diaphragmatic pillars. The anatomical structures analyzed were similar to those reported for other mammals. Histological analysis revealed stable, organized muscle fibers with alternation of light and dark streaks, indicating transverse striation.

Ultrasound-guided identification of the cricothyroid membrane in a patient with a difficult airway: a case report

BACKGROUND

Surgical cricothyroidotomy is considered to be the last resort for management of the difficult airway. A major point for a successful surgical cricothyroidotomy is to identify the location of the cricothyroid membrane.

CASE PRESENTATION

We encountered a patient with progressive respiratory distress who was anticipated to have a difficult airway due to a large neck abscess. We prepared for both awake intubation and surgical cricothyroidotomy. The cricothyroid membrane could not be identified by palpation, but was readily identified using ultrasound.

CONCLUSION

Ultrasound-guided identification of the cricothyroid membrane may be useful in a patient with a difficult airway due to neck swelling.

Ultrasound comparison of external and internal neck anatomy with the LMA Unique

Introduction

Internal neck anatomy landmarks and their relation after placement of an extraglottic airway devices have not been studied extensively by the use of ultrasound. Based on our group experience with external landmarks as well as internal landmarks evaluation with other techniques, we aimed use ultrasound to analyze the internal neck anatomy landmarks and the related changes due to the placement of the Laryngeal Mask Airway Unique.

Methods

Observational pilot investigation. Non-obese adult patients with no evidence of airway anomalies, were recruited. External neck landmarks were measured based on a validated and standardized method by tape. Eight internal anatomical landmarks, reciprocal by the investigational hypothesis to the external landmarks, were also measured by ultrasound guidance. The internal landmarks were re-measured after optimal placement and inflation of the extraglottic airway devices cuff Laryngeal Mask Airway Unique.

Results

Six subjects were recruited. Ultrasound measurements of hyoid-mental distance, thyroid-cricoid distance, thyroid height, and thyroid width were found to be significantly (p < 0.05) overestimated using a tape measure. Sagittal neck landmark distances such as thyroid height, sternal-mental distance, and thyroid-cricoid distance significantly decreased after placement of the Laryngeal Mask Airway Unique.

Conclusion

The laryngeal mask airway Unique resulted in significant changes in internal neck anatomy. The induced changes and respective specific internal neck anatomy landmarks could help to design devices that would modify their shape accordingly to areas of greatest displacement. Also, while external neck landmark measurements overestimate their respective internal neck landmarks, as we previously reported, the concordance of each measurement and their respective conversion factor could continue to be of help in sizing extraglottic airway devices. Due to the pilot nature of the study, more investigations are warranted.

Can thyromental distance be measured accurately?

Using the thyromental distance (TMD) measured based on the ultrasonographic location of the thyroid cartilage prominence as the criterion, we investigated the accuracy of TMD measurement by surface landmark identification of the thyroid cartilage prominence. Twenty-nine anesthetist resident volunteers were recruited, including 10 first-year residents, 9 second-year residents and 10 third-year residents. Each volunteer measured the other 28 volunteers’ TMD. Then, the thyroid cartilage prominence of each volunteer was identified by ultrasonography of the junction of the vocal cord and thyroid cartilage, and the TMD was measured precisely. The error of the TMD measurement was determined by the minimal detectable difference (MDD) compared to the ultrasound measurement. A difference of greater than 5.4 mm between the TMD measured by volunteers and that based on ultrasound localization was defined as a measurement error. The measurement error rate of females’ TMD was significantly higher than that of males’ (50 vs 10%, P < 0.001). The error rates of anesthetist residents of first-year, second-year and third-year were 34, 27, and 31%, respectively, and were not significantly different. The error of TMD measurement by surface landmark identification is often, especially for women. More clinic experience don’t improve it.

A comparative prospective cohort study comparing physical exam to ultrasound for identifying the cricoid cartilage

Applying cricoid pressure is a common practice when intubating patients thought to be at risk of pulmonary aspiration. Recently, the perceived benefits of applying cricoid pressure have been questioned. Prior research has shown that cricoid pressure is applied incorrectly and that palpation of adjacent anatomy of the cricothyroid membrane is also inaccurate. We compared physical palpation to ultrasound for identifying the location of the cricoid cartilage using a total of 50 assessments. The median distance to target was 10 mm. We concluded that palpation is an inaccurate method to locate the cricoid cartilage in the studied population.

Determining the amount of training needed for competency of anesthesia trainees in ultrasonographic identification of the cricothyroid membrane

Background

Airway guidelines recommend the use of ultrasound to localize the cricothyroid membrane prior to airway manipulation in difficult airways. In this study, we aimed to determine the amount of training anesthesia trainees would need to achieve competence in bedside ultrasound to identify the cricothyroid membrane.

Methods

This is a prospective non-randomized cohort study in the Department of Anesthesia at Mount Sinai Hospital (Toronto, Ontario, Canada). Following institutional ethics approval, six anesthesia trainees consisting of four residents and two fellows underwent a 2-h training session on neck ultrasound to identify neck landmarks and the cricothyroid membrane. The trainees had no previous airway ultrasound experience. One-two weeks later, each trainee performed consecutive neck ultrasound scans on 20 healthy volunteers to identify the cricothyroid membrane. Cumulative sum (CUSUM) learning curves were constructed for each trainee. Primary outcome was the number of ultrasound examinations required to achieve competence, defined as 90% success rate in a series of 20 ultrasound scans. Secondary outcomes were the overall success rate, the time (sec.) required to perform the task, and 3-month skills assessment.

Results

CUSUM analysis showed four trainees achieved competence with a mean [range] success rate of 94.0% [90–100%] and a median [range] number of attempts of 14 [9–18]. Two trainees did not achieve competence, but obtained a success rate of 75.0 and 80.0% each. Overall (number of attempts) success rate was 88.3% (106/120) with a mean (SD) time of 36.9 (9.0) sec. Three months after training, ultrasound of five consecutive neck scans showed a mean success rate of 86.7% (26/30) and mean (SD) time of 47.7 (16.0) sec.

Conclusions

After a short 2-h training session, most anesthesia trainees (n = 4/6) achieved competence in ultrasound-identification of the cricothyroid membrane with less than 20 scans in a mean time less than 60 s., and that they remain reasonably competent 3 months later. The learning curve for ultrasound identification of the cricothyroid membrane seems to be short even without prior airway ultrasound experience.

Emergency Cricothyrotomy Performed by Surgical Airway-naive Medical Personnel: A Randomized Crossover Study in Cadavers Comparing Three Commonly Used Techniques

BACKGROUND

When conventional approaches to obtain effective ventilation and return of effective spontaneous breathing fail, surgical airway is the last rescue option. Most physicians have a limited lifetime experience with cricothyrotomy, and it is unclear what method should be taught for this lifesaving procedure. The aim of this study is to compare the performance of medical personnel, naive to surgical airway techniques, in establishing an emergency surgical airway in cadavers using three commonly used cricothyrotomy techniques.

METHODS

Twenty medical students, without previous knowledge of surgical airway techniques, were randomly selected from their class. After training, they performed cricothyrotomy by three techniques (surgical, Melker, and QuickTrach II) in a random order on 60 cadavers with comparable biometrics. The time to complete the procedure, rate of success, and number of complications were recorded. A success was defined as the correct placement of the cannula within the trachea in 3 min.

RESULTS

The success rates were 95, 55, and 50% for surgical cricothyrotomy, QuickTrach, and Melker, respectively (P = 0.025). The majority of failures were due to cannula misplacement (15 of 20). In successful procedures, the mean procedure time was 94 ± 35 s in the surgical group, 77 ± 34 in the QuickTrach II group, and 149 ± 24 in the Melker group (P < 0.001). Few significant complications were found in successful procedures. No cadaver biometric parameters were correlated with success of the procedure.

CONCLUSION

Surgical airway-naive medical personnel establish emergency cricothyrotomy more efficiently and safely with the surgical procedure than with the other two commonly used techniques.