Ultrasound as an Assessment Method in Predicting Difficult Intubation: A Prospective Clinical Study

Machine learning models based on ultrasound and physical examination for airway assessment

PURPOSE

To demonstrate the utility of machine learning models for predicting difficult airways using clinical and ultrasound parameters.

METHODS

This is a prospective non-consecutive cohort of patients undergoing elective surgery. We collected as predictor variables age, sex, BMI, OSA, Mallampatti, thyromental distance, bite test, cervical circumference, cervical ultrasound measurements, and Cormack-Lehanne class after laryngoscopy. We univariate analyzed the relationship of the predictor variables with the Cormack-Lehanne class to design machine learning models by applying the random forest technique with each predictor variable separately and in combination. We found each design's AUC-ROC, sensitivity, specificity, and positive and negative predictive values.

RESULTS

We recruited 400 patients. Cormack-Lehanne patients≥III had higher age, BMI, cervical circumference, Mallampati class membership≥III, and bite test≥II and their ultrasound measurements were significantly higher. Machine learning models based on physical examination obtained better AUC-ROC values than ultrasound measurements but without reaching statistical significance. The combination of physical variables that we call the "Classic Model" achieved the highest AUC-ROC value among all the models [0.75 (0.67-0.83)], this difference being statistically significant compared to the rest of the ultrasound models.

CONCLUSIONS

The use of machine learning models for diagnosing VAD is a real possibility, although it is still in a very preliminary stage of development.

CLINICAL REGISTRY

ClinicalTrials.gov: NCT04816435.

Ultrasound predictive parameters of difficult airway in thyroid surgery: a pilot study

Difficult airway is a major life-threatening complication during induction of general anesthesia. In thyroid surgery, intubation could be complicated by airway distortion because of the enlarged thyroid gland. Recently, ultrasonography has been proposed as a potential modality for airway assessment and management. The aim of the study is to evaluate ultrasound-based measurement of airway parameters in 13 selected patients with compressive goiter and tracheal deviation scheduled for thyroidectomy before induction of general anesthesia. Specifically, we detected the distance between the skin and retro-isthmic trachea (DSRIT) and the distance between the sub isthmic trachea and the carotid artery (DCSIT) at the side of the dominant lobe. We compared ultrasound measures before intubation with Cormack-Lehane laryngoscopes grades recorded during tracheal intubation.

Bedside Ultrasound: The Silent Guardian for Upper Airway Assessment and Management

Ultrasound evaluation of the upper airway has emerged as an essential instrument for clinicians, offering real-time assessment that can help to guide interventions and improve patient outcomes. This review aims to provide health care providers with a practical approach to performing ultrasound evaluation of the upper airway, covering basic physics relevant to upper airway ultrasound, the identification of key anatomical structures, and elucidating its various clinical applications, such as prediction of difficult airway, confirmation of endotracheal intubation, and guidance for surgical airway procedures and airway blocks. We also discuss evidence-based training programs, limitations, and future directions of ultrasound imaging of the upper airway.

Value of the Hyomental Distance Measured With Ultrasound in Forecasting Difficult Laryngoscopy in Newborns

PURPOSE

Preoperative evaluations of difficult airways are imperative, especially in newborns. The hyomental distance is a reliable index for predicting difficult airways in adults. However, few studies have evaluated the value of the hyomental distance for predicting difficult airways in newborns. It is unclear whether the hyomental distance forecasts a restricted or difficult view when using direct laryngoscopy. We intended to develop an effective system for predicting difficult tracheal intubation in newborns.

DESIGN

A prospective observational clinical study.

METHODS

Newborns aged 0 to 28 days undergoing oral endotracheal intubation with direct laryngoscopy for elective surgery under general anesthesia were enrolled. The hyomental distance and hyoid level tissue thickness were assessed by ultrasound. Other parameters, such as the mandibular length and sternomental distance, were also evaluated before anesthesia. The glottic structure view under laryngoscopy was graded according to the Cormack-Lehane classification. The patients with Grade 1 and 2 laryngeal views were assigned to Group E. Those with Grade 3 and 4 views were assigned to Group D.

FINDINGS

A total of 123 newborns were recruited for our study. The incidence of poor visualization of the larynx during laryngoscopy in our study was 10.6%. The multifactor logistic regression results showed that the hyomental distance was a powerful predictor of difficult laryngoscopy (OR = 0.16, 95% CI 0.03-0.74, P = .019). The curve with the highest sensitivity and specificity and the maximum area under the curve (AUC) was the hyomental distance. The receiver operating characteristic (ROC) curve for the hyomental distance suggested that the best cut-off value was less than equal to 2.74 cm, with an AUC of 0.80 (95% CI 0.64-0.95).

CONCLUSIONS

It is noninvasive and feasible to accurately measure the hyomental distance with ultrasound in newborns, and the results are reliable. We believe that the hyomental distance measured with ultrasound could be used as a marker for predicting difficult laryngoscopy in newborns.

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.

Role of ultrasound in acute respiratory failure and in the weaning of mechanical ventilation

Comprehensive ultrasound assessment has become an essential tool to facilitate the diagnosis and therapeutic management of critically ill patients with acute respiratory failure (ARF). There is evidence supporting the use of ultrasound for the diagnosis of pneumothorax, acute respiratory distress syndrome, cardiogenic pulmonary edema, pneumonia and acute pulmonary thromboembolism, and in patients with COVID-19. In addition, in recent years, the use of ultrasound to evaluate responses to treatment in critically ill patients with ARF has been developed, providing a noninvasive tool for titrating positive end-expiratory pressure, monitoring recruitment maneuvers and response to prone position, as well as for facilitating weaning from mechanical ventilation. The objective of this review is to summarize the basic concepts on the utility of ultrasound in the diagnosis and monitoring of critically ill patients with ARF.

Role of Point-of-Care Ultrasound in Emergency Airway Management Outside the Operating Room

Tracheal intubation is one of the most frequently performed procedures in critically ill patients, and is associated with significant morbidity and mortality. Hemodynamic instability and cardiovascular collapse are common complications associated with the procedure, and are likely in patients with a physiologically difficult airway. Bedside point-of-care ultrasound (POCUS) can help identify patients with high risk of cardiovascular collapse, provide opportunity for hemodynamic and respiratory optimization, and help tailor airway management plans to meet individual patient needs. This review discusses the role of POCUS in emergency airway management, provides an algorithm to facilitate its incorporation into existing practice, and provides a framework for future studies.

Prediction of Difficult Laryngoscopy Using Ultrasound: A Systematic Review and Meta-Analysis

OBJECTIVES

Evaluate associations between ultrasound measures and difficult laryngoscopy.

DATA SOURCES

MEDLINE, Embase, Google Scholar, Web of Science, and the Cochrane Library were searched using MeSH terms and keywords.

STUDY SELECTION

Studies published in English describing the use of airway ultrasound for identifying difficult laryngoscopy, with sufficient data to calculate sensitivity and specificity using 2 × 2 tables.

DATA EXTRACTION

We assigned the described indices of airway dimension to one of three domains based on methodology characteristics: anterior tissue thickness domain, anatomical position domain, and oral space domain. We then performed a bivariate random-effects meta-analysis, deriving pooled sensitivity, specificity, diagnostic odds ratio, positive likelihood ratio, and negative likelihood ratio estimates. We assessed risks of bias using Quality Assessment of Diagnostic Accuracy Studies-2 analysis.

DATA SYNTHESIS

Thirty-three studies evaluating 27 unique indices were included in the meta-analysis. The ultrasound protocols of the included studies were heterogeneous. Anterior tissue thickness demonstrated a pooled sensitivity of 76% (95% CI, 71-81%), specificity of 77% (95% CI, 72-81%), and an area under the receiver operating characteristic curve (AUROC) of 0.83 (95% CI, 0.80-0.86). Anatomical position demonstrated a pooled sensitivity of 74% (95% CI, 61-84%), specificity of 86% (95% CI, 78-91%), and an AUROC of 0.87 (95% CI, 0.84-0.90). Oral space demonstrated a pooled sensitivity of 53% (95% CI, 0.36-0.69), specificity of 77% (95% CI, 0.67-0.85), and an AUROC of 0.73 (95% CI, 0.69-0.77).

CONCLUSIONS

Airway ultrasound metrics associate with difficult laryngoscopy in three domains: anterior tissue thickness, anatomic position, and oral space. An assessment instrument combining clinical and ultrasound assessments may be an accurate screening tool for difficult laryngoscopy.

2022 American Society of Anesthesiologists Practice Guidelines for Management of the Difficult Airway

The American Society of Anesthesiologists; All India Difficult Airway Association; European Airway Management Society; European Society of Anaesthesiology and Intensive Care; Italian Society of Anesthesiology, Analgesia, Resuscitation and Intensive Care; Learning, Teaching and Investigation Difficult Airway Group; Society for Airway Management; Society for Ambulatory Anesthesia; Society for Head and Neck Anesthesia; Society for Pediatric Anesthesia; Society of Critical Care Anesthesiologists; and the Trauma Anesthesiology Society present an updated report of the Practice Guidelines for Management of the Difficult Airway.

Airway Ultrasound as Predictor of Difficult Direct Laryngoscopy: A Systematic Review and Meta-analysis

Despite several clinical index tests that are currently applied for airway assessment, unpredicted difficult laryngoscopy may still represent a serious problem in anesthesia practice. The aim of this systematic review and meta-analysis was to evaluate whether preoperative airway ultrasound can predict difficult direct laryngoscopy in adult patients undergoing elective surgery under general anesthesia.

Comparative study of the reliability of ultrasound to confirm the position of endotracheal tube with cuff inflated with saline versus air

Aim: To compare the reliability of transtracheal ultrasound to confirm the endotracheal tube position with saline versus air inflated cuff. Methods: This was a prospective randomized cadaveric study. Four techniques were randomized: endotracheal tube in the trachea with air or saline inflated cuff, and endotracheal tube in the esophagus with air or saline inflated cuff. The investigator used the Mcgrath to randomly place the endotracheal tube in the trachea or in the esophagus with saline or air inflated cuff. During the first series of measurements, nine residents performed transtracheal ultrasound with linear transducer placed transversely at the suprasternal notch. They were recorded with a cut off fixed to 30 seconds, and a questionnaire was completed by the residents after each transtracheal ultrasound in order to report where the endotracheal tube is positioned according to them. The second series followed the same protocol and included three residents who had participated in the first series. The primary outcome was the success rate in determining the position of the endotracheal tube. Results: In the first series, the success rate was 46.5%. In the second series, the success rate was 72.9%. There was no significant difference between cuff inflated with saline and air (p = 1.00). The overall mean time required was 20.6 s (95% CI 13.0–28.2 s). Based on an empirical data set, transtracheal ultrasound had a sensitivity of 62.2%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 26.08%. Conclusion: This investigation shows that regardless of the contents of the endotracheal tube cuff, the use of transtracheal ultrasound to confirm the position of endotracheal tube reports disappointing results.

Ultrasonography indicators for predicting difficult intubation: a systematic review and meta-analysis

Background

Ultrasonography (US) is recently used frequently as a tool for airway assessment prior to intubation (endotracheal tube (ETT) placement), and several indicators have been proposed in studies with different reported performances in this regard. This systematic review and meta-analysis reviewed the performance of US in difficult airway assessment.

Methods

This systematic review and meta-analysis was conducted according to the guideline of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and the Cochrane book. All the studies that had carried out difficult airway assessments using US, had compared the indicators in difficult and easy groups, and had published the results in English by the time we conducted our search in April 28, 2020, were included.

Results

In the initial search, 17,156 articles were retrieved. After deleting the duplicate articles retrieved from multiple databases, 7578 articles remained for screening based on the abstracts and titles. Finally, the full text of 371 articles were assessed and the data from 26 articles were extracted, which had examined a total of 45 US indicators for predicting difficult intubation. The most common US index was the “thickness of anterior neck soft tissue at the vocal cords level”. Also, “skin to epiglottis” and “anterior neck soft tissue at the hyoid bone level” were among the most common indicators examined in this area.

Conclusion

This systematic review showed that US can be used for predicting difficult airway. Of note, “skin thickness at the epiglottis and hyoid levels”, “the hyomental distance”, and “the hyomental distance ratio” were correlated with difficult laryngoscopy in the meta-analysis. Many other indicators, including some ratios, have also been proposed for accurately predicting difficult intubation, although there have been no external validation studies on them.

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.

Use of Handheld Point-of-Care Ultrasound in Emergency Airway Management

Emergency airway management (EAM) is associated with a high rate of complications, morbidity, and mortality. Handheld point-of-care ultrasound shows promise as an emerging technology to facilitate rapid screening for difficult laryngoscopy, identify the cricothyroid membrane for potential cricothyroidotomy, and assess for increased aspiration risk, as well as provide confirmation of proper endotracheal tube positioning. This review summarizes the available evidence for the use of point-of-care ultrasound in EAM, provides an algorithm to facilitate its incorporation into existing EAM practice to improve patient safety, and serves as a framework for future validation studies.

Ultrasound for predicting difficult airway in obstetric anesthesia: Protocol and methods for a prospective observational clinical study

BACKGROUND

Failed intubation and ventilation during cesarean deliveries are important causes of anesthetic-related maternal mortality. Due to the physiological changes in airway anatomy, parturient had higher incidences of difficult airway than non-obstetric population. Accurate airway assessment is the first step and the most important in airway management. However, the common clinical screening tests, shown low sensitivity and specificity with a limited predictive value. Ultrasound is a quick, noninvasive, inexpensive tool, with the advancement of ultrasound technology, modern ultrasound machine is more portable with better resolution and enhanced tissue penetration, provide better imaging in tissues like epiglottis, vocal cords, ring-shaped membrane, and can be used in airway assessment. Here, the aim of the current study was to find whether preoperative ultrasound assessment of neck anatomy can predict difficult airway in parturient, and provide new ideas and a theoretical basis in the airway management of obstetric anesthesia.

METHODS

This is a prospective, observational single-blinded study in a single-center. Subjects will be recruited from patients aged from 18 to 60 years, gestational age ≥ 36 weeks, scheduled for cesarean section under general anesthesia and tracheal intubation. Ultrasound measurement will be performed to detect anterior cervical soft tissue thickness at five anatomical levels (hyoid bone, epiglottis, cricothyroid membrane, thyroid isthmus and suprasternal notch) in the upper airway. The thickness of the soft tissue in the front of the neck and clinical airway measurements will be compared between the "easy intubation" and "difficult intubation" group divided by Cormack-Lehane grade. Receiver-operating characteristic curves were used to determine the sensitivity and specificity of "difficulty prediction capability" of each sonographic and physical measurements. Clinical factors associated with difficult intubation will be determined by univariate analyses. Multiple logistic regression analysis performed to determine independent predictors of difficult intubation.

CONCLUSIONS

The study outlined in this protocol will explore the possibility of ultrasound for predicting difficult airway in obstetric anesthesia. This may provide new insight into the practice of airway management.

TRIAL REGISTRATION

Chinese Clinical Trial Registry, ChiCTR1800018949.