Ultrasound Quantification of Anterior Soft Tissue Thickness Fails to Predict Difficult Laryngoscopy in Obese Patients

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

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

Evaluation of preoperative difficult airway prediction methods for adult patients without obvious airway abnormalities: a systematic review and meta-analysis

BACKGROUND

This systematic review aims to assist clinical decision-making in selecting appropriate preoperative prediction methods for difficult tracheal intubation by identifying and synthesizing literature on these methods in adult patients undergoing all types of surgery.

METHODS

A systematic review and meta-analysis were conducted following PRISMA guidelines. Comprehensive electronic searches across multiple databases were completed on March 28, 2023. Two researchers independently screened, selected studies, and extracted data. A total of 227 articles representing 526 studies were included and evaluated for bias using the QUADAS-2 tool. Meta-Disc software computed pooled sensitivity (SEN), specificity (SPC), positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR). Heterogeneity was assessed using the Spearman correlation coefficient, Cochran's-Q, and I2 index, with meta-regression exploring sources of heterogeneity. Publication bias was evaluated using Deeks' funnel plot.

RESULTS

Out of 2906 articles retrieved, 227 met the inclusion criteria, encompassing a total of 686,089 patients. The review examined 11 methods for predicting difficult tracheal intubation, categorized into physical examination, multivariate scoring system, and imaging test. The modified Mallampati test (MMT) showed a SEN of 0.39 and SPC of 0.86, while the thyromental distance (TMD) had a SEN of 0.38 and SPC of 0.83. The upper lip bite test (ULBT) presented a SEN of 0.52 and SPC of 0.84. Multivariate scoring systems like LEMON and Wilson's risk score demonstrated moderate sensitivity and specificity. Imaging tests, particularly ultrasound-based methods such as the distance from the skin to the epiglottis (US-DSE), exhibited higher sensitivity (0.80) and specificity (0.77). Significant heterogeneity was identified across studies, influenced by factors such as sample size and study design.

CONCLUSION

No single preoperative prediction method shows clear superiority for predicting difficult tracheal intubation. The evidence supports a combined approach using multiple methods tailored to specific patient demographics and clinical contexts. Future research should focus on integrating advanced technologies like artificial intelligence and deep learning to improve predictive models. Standardizing testing procedures and establishing clear cut-off values are essential for enhancing prediction reliability and accuracy. Implementing a multi-modal predictive approach may reduce unanticipated difficult intubations, improving patient safety and outcomes.

Ultrasound-based airway assessment in obese patients as a valuable tool for predicting difficult airway: an observational study

BACKGROUND

Difficult airway, characterized by difficult mask ventilation and intubation, is common in obese patients undergoing surgery. The purpose of this study was to evaluate and compare the prognostic efficiency of ultrasound-measured anterior cervical soft tissue parameters as an indicator of difficult airway during anesthesia induction in obese patients.

METHODS

This prospective, double-blind, observational study was conducted at Balikesir University Faculty of Medicine Hospital between March 2020 and March 2022. A total of 157 patients age ≥ 18 (BMI ≥ 30 kg.m-2), without previous head and neck surgery were included in the study. Anterior cervical soft tissue measurements were performed at three levels; minimum distance between the hyoid bone and skin at the level of the hyoid bone; (DSHB), distance between the midpoint of the epiglottis and skin at the level of the thyrohyoid membrane; (DSE), distance between the anterior commissure of vocal cords and skin at the vocal cord level; (DSV). The Han scale was used to assess difficult mask ventilation and the Cormack-Lehane scale was used to assess difficult laryngoscopy.

RESULTS

In the difficult laryngoscopy group, the mean values of DSHB, DSE and DSV were 18.5 ± 3.5, 18.3 ± 3.8, and 18.6 ± 3.4, respectively. The AUC values for DSHB, DSE, and DSV were 0.845, 0.827, and 0.850, respectively. Anterior cervical measurements showed a better predictive value for difficult laryngoscopy compared to difficult mask ventilation.

CONCLUSION

Ultrasonographic measurements were predictive for difficult laryngoscopy and ventilation with better correlation in laryngoscopy.

Determinants of difficult laryngoscopy based on upper airway indicators: a prospective observational study

BACKGROUND

The main cause of anesthesia-related deaths is the failure to manage difficult airways. Difficult laryngoscopic exposure is a major cause of unsuccessful management of difficult airways. Inadequate preoperative airway assessment hinders the clinical management of difficult airways cases, emphasizing the critical need for accurate identification of difficult airways. Currently, no definitive and reliable indicators are available to predict a difficult airway. Our study aims to predict laryngoscope exposure risk factors by combining ultrasonically measured upper airway anatomic parameters with physical examination indicators.

METHODS

Patients aged 18 to 75 years, classified as American Standards Association (ASA) I-III, and scheduled for elective general anesthesia with endotracheal intubation were included. All patients received the upper airway and ultrasonographic measurements. After anesthesia induction, laryngoscope exposure was analyzed using the Cormack-Lehane grading system, with Grades III and IV as indicative of difficult laryngoscopy. Univariate and multivariate logistic regression analyses were performed to identify reliable indicators for predicting difficult laryngoscopy. Receiver Operating Characteristic (ROC) curve analysis was utilized to assess the predictive performance of each indicator.

RESULTS

A total of 1120 patients finished the study, with 710 cases found in Grade I laryngoscopic exposure group, 360 cases in Grade II group, and 50 cases in Grade III group. There was no case observed in Grade IV group, thereby resulting in an incidence of difficult laryngoscopy of 4.46%. Univariate logistic regression analysis revealed that several parameters including age, Body Mass Index (BMI), neck circumference, neck mobility, snoring intensity, as well as ultrasound measurements of the pre-epiglottic space and thyromental distance were identified as significant risk factors for difficult laryngoscopy (P < 0.05). Among these, BMI, and neck circumference exhibited notable predictive value, with Area Under The Curve (AUC) values of 0.746 (95%CI 0.649-0.842) and 0.732 (95%CI 0.638-0.827), respectively. Neck mobility was also identified as an independent risk factor for predicting difficult laryngoscopy (P = 0.009) in multivariate logistic regression analysis, with an AUC of 0.672 (0.562-0.782) in the ROC curve.

CONCLUSIONS

Our findings revealed a direct correlation between difficult laryngoscopy and age, BMI, neck circumference, neck mobility, snoring intensity, as well as ultrasound measurements of the pre-epiglottic space and thyromental distance. Furthermore, neck mobility was identified as an independent predictive factor.

TRIAL REGISTRATION

The trial was registered prior to patient enrollment at clinicaltrials.gov (register no. ChiCTR2100053826, Date of registration: November 30, 2021).

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

BACKGROUND

Ultrasonographic imaging has been recently become simple portable and non-invasive adjuvant for bedside assessment of anterior neck soft tissue thickness which when measured at different levels showed to have significant role in predicting difficult laryngoscopy.

AIMS AND OBJECTIVES

Primary objective was Ultrasonographic measurement of anterior neck soft tissue thickness at 3 levels -Distance from skin to hyoid bone (DSHB) -Distance from skin to thyrohyoid membrane (DSTM) -Distance from skin to anterior commissure of vocal cord(DSAC) and to compare and correlate the findings with Cooks modification of Cormack-Lehane score in predicting difficult laryngoscopy. Secondary objective was to compare and correlate the ultrasonographic measurements with conventional airway assessment methods.

MATERIALS AND METHODS

After obtaining approval from the ethical committee, 90 Patients with BMI above 25 kg /m2 was enrolled for the study. A day before the surgery a thorough Preanaesthetic evaluation and assessment of the airway is done using conventional methods. Then on the day of surgery ultrasonographic measurement of anterior neck at 3 levels was done and after inducing the patients laryngoscopy was done and Cooks modification of Cormack-Lehane score assessed.

RESULTS

The optimal cut off values to predict difficult laryngoscopy was 1.26, 2 and 1.2 cms for DSHB, DSTM and DSAC respectively, and among the three skin to anterior commissure of vocal cord was observed to be best USG parameter with more area under the ROC curve.

CONCLUSION

USG measurement of anterior neck soft tissue thickness can be useful in predicting difficult laryngoscopy in overweight and obese patients also it had more diagnostic accuracy than conventional methods like MMS in predicting difficult laryngoscopy.

Point-of-care ultrasound for airway management in the emergency and critical care setting

Airway management is a common procedure within emergency and critical care medicine. Traditional techniques for predicting and managing a difficult airway each have important limitations. As the field has evolved, point-of-care ultrasound has been increasingly utilized for this application. Several measures can be used to sonographically predict a difficult airway, including skin to epiglottis, hyomental distance, and tongue thickness. Ultrasound can also be used to confirm endotracheal tube intubation and assess endotracheal tube depth. Ultrasound is superior to the landmark-based approach for locating the cricothyroid membrane, particularly in patients with difficult anatomy. Finally, we provide an algorithm for using ultrasound to manage the crashing patient on mechanical ventilation. After reading this article, readers will have an enhanced understanding of the role of ultrasound in airway management.

A new score for airway assessment using clinical and ultrasound parameters

Background

Over the last few years, ultrasonography has been introduced as the fifth pillar to patient's bedside physical examination. Clinical assessments aim to screen and look for airway difficulties to predict difficult intubations, but none have demonstrated a significant predictive capacity. Recent systematic reviews have established a correlation between ultrasound imaging and difficult direct laryngoscopy. The primary objective of this study was to determine whether the utilization of ultrasonography to examine the upper airway could accurately predict difficult direct laryngoscopy.

Methods

This is a prospective observational study including 102 adult patients that required general anesthesia for elective surgery. Preoperatively, clinical airway assessments were performed. Data such as Mallampati-Samsoon grade (MS), upper lip bite test (ULBT), thyromental (TMD) and sternomental distance (SMD), cervical circumference (CC) and the Arné risk index were collected. Ultrasound evaluation was taken at five different levels in two planes, parasagittal and transverse. Therefore, the following measurements were registered: distance from skin to hyoid bone (DSHB), distance from skin to thyrohyoid membrane (DSTHM), distance from skin to epiglottis (DSE), distance from skin to thyroid cartilage (DSTC) and distance from hyoid bone and thyroid cartilage (DHBTC). Patients were divided into two groups based on the difficulty to perform direct laryngoscopy, according to Cormack-Lehane (C-L) classification. Grades I and II were classified as easy laryngoscopy and grades III or IV as difficult. Logistic regression models and the Receiver Operating Characteristic (ROC) curve was employed to determine the diagnostic precision of ultrasound measurements to distinguish difficult laryngoscopy (DL).

Results

The following risk score for DL was obtained, DSTHM ≥ 1.60 cm (2 points), DSTC ≥ 0.78 cm (3 points) and gender (2 points for males). The score can range from 0 to 7 points, and showed and AUC (95% CI) of 0.84 (0.74-0.95). A score of 5 points or higher indicates a 34-fold increase in the risk of finding DL (p = 0.0010), sensitivity of 91.67, specificity of 75.56, positive predictive value of 33.33, and negative predictive value of 98.55.

Conclusion

The use of ultrasonography combined with classic clinical screening tests are useful tools to predict difficult direct laryngoscopy.

Ultrasound-Guided Airway Evaluation: Is It a Game Changer for Predicting Difficult Endotracheal Intubation?

INTRODUCTION

Airway ultrasound has recently promised to be a valuable addition to preoperative airway assessment tools. This study was undertaken to determine the efficacy of ultrasound-guided measurement of soft tissue thickness (STT) at various levels of the anterior neck in predicting difficult airways in an eastern Indian population.

OBJECTIVE

 The primary objective was to find out the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of anterior neck soft tissue thickness at the level of the hyoid (STT-Hyoid) and vocal cords (STT-VC), distance from the skin to the epiglottis midway (DSEM), and the ratio of the depth of the pre-epiglottic space (Pre-E) to the distance from the epiglottis to the mid-point of the vocal cords (E-VC). The secondary objective was to develop a scoring system using these parameters.

MATERIALS AND METHODS

One hundred eighty-eight patients aged 18-65 years who received general anesthesia and endotracheal intubation for surgery were included in the study. Anterior neck soft tissue thickness measurements were done preoperatively using ultrasound. The actual difficulty of the airway was graded by the anesthesiologist while performing endotracheal intubation using the intubation difficulty scale (IDS).

RESULTS

The incidence of a difficult airway (IDS > 5) was 9.04%. The STT-Hyoid and STT-VC had a moderate correlation with IDS. The DSEM and Pre-E/E-VC ratios had a weak correlation with IDS. For difficult airway prediction, the cutoff points of STT-Hyoid and STT-VC were 7.95 mm and 24.25 mm, respectively. The combined cutoff measurements of STT-Hyoid and STT-VC (29.95 mm) were better predictors of difficult airway.

CONCLUSION

Preoperative airway ultrasound examination measuring the soft tissue thickness at the hyoid and vocal cord levels is an effective modality in predicting a difficult airway. However, further studies are needed to validate this finding in populations of varied ethnicity and demographic distribution.

Mean distance from skin to epiglottis in parturients as measured by airway ultrasound

Introduction

There is an increasing interest in using airway ultrasound to predict difficult intubation. Studies to date have excluded pregnant women in reporting airway measurements. We performed this study to compare the mean distance from skin to epiglottis in parturients to that reported in previously published studies. We also assessed the correlation of mean distance from skin to epiglottis with other elements of the airway examination.

Methods

A total of 100 parturients were recruited from a tertiary hospital's labor and delivery floor. Standard physical examination parameters were recorded in addition to the mean distance from skin to epiglottis for all subjects. The ratio of height-to-thyromental distance was used to classify airways as potentially favorable or unfavorable.

Results

The average mean distance from skin to epiglottis in parturients was 19.9 ± 3.3 mm and followed a normal distribution. The mean distance from skin to epiglottis was moderately correlated with height and body mass index. There was no difference in mean distance from skin to epiglottis between subjects with favorable versus unfavorable airways as classified by ratio of height-to-thyromental distance.

Conclusion

The typical mean distance from skin to epiglottis in parturients falls between previously published values in mixed populations. Previously published cut-off values using airway ultrasound to predict difficult intubation are not likely to apply to parturients.

Preoperative airway ultrasound assessment in the sniffing position: a prospective observational study

BACKGROUND

Clinical airway screening tests intend to predict difficult airways, but none have a high predictive value. Recent systematic reviews correlate ultrasound with difficult laryngoscopy. This study aimed primarily to correlate ultrasound measurements of anatomical upper airway structures in the sniffing position with difficult direct laryngoscopy. The secondary aim was to observe gender-based differences.

METHODS

This prospective, cross-sectional, single-center observational study included 209 patients requiring general anesthesia for elective surgery. Preoperatively, we performed six clinical airway assessments and three ultrasound measurements, which were the Distance from Skin to the Hyoid Bone (DSHB), to the Epiglottis (DSE), and to the anterior commissure of the vocal cords (DSAC) in a sniffing position. Benumof's criteria for the "best view at the first attempt" for direct laryngoscopy assessed the difficulty of laryngoscopy.

RESULTS

The distance from skin to the epiglottis was the best predictor of direct difficult laryngoscopy (defined as Cormack-Lehane grade ≥ 2b) with a minimum thickness cut-off at 2.70 ± 0.19 cm (sensitivity 91.3%; specificity 96.9%). The skin to the hyoid bone distance cut-off was 1.41 ± 0.30 cm with moderate correlation (sensitivity 80.4%; specificity 60.1%). No correlation was found for the distance to the anterior commissure of the vocal cords. In women compared to men, the skin to the epiglottis distance was more sensitive (92.3% vs. 90.9%) and specific (98.8% vs. 95.2%).

CONCLUSIONS

DSE in the sniffing position is the most reliable parameter for preoperative airway ultrasound assessment in the Caucasian population, with higher sensitivity and specificity in women, and might be considered as an independent predictor for direct difficult laryngoscopy.

Prediction of difficult laryngoscopy / difficult intubation cases using upper airway ultrasound measurements in emergency department: a prospective observational study

INTRODUCTION

Difficult laryngoscopy and intubation are serious problems among critically ill patients in emergency department (ED) so utility of a rapid, accurate and noninvasive method for predicting of these patients are necessary. Ultrasonography has been recently used in this regard and this study was conducted to investigate the correlation of some introduced upper airway ultrasound parameters with difficult laryngoscopy / difficult intubation in patients referred to the ED.

METHOD

In this prospective observational study all patients ≥ 18-year-old who had an indication for rapid sequence intubation (RSI) were included. Ultrasound parameters including Hyoid Bone Visibility (HBV), Distance from Skin to Hyoid Bone (DSHB), Distance from Skin to Vocal Cords (DSVC), Distance from Skin to Thyroid Isthmus (DSTI), and Distance between Arytenoids Cartilages (DBAC) were measured in all cases. The patients underwent RSI and thereafter the patients' baseline characteristics, Cormack-Lehane grade, number of attempted laryngoscopy were recorded in a pre-prepared check list and compared with measured ultrasound parameters. The "difficult laryngoscopy" was defined as Cormack-Lehane classification grades III/IV; and need for more than 3 intubation attempts was considered as "difficult intubation".

RESULTS

One hundred and twenty-three patients (52% male) were included of whom 10 patients (8.1%) were categorized as difficult laryngoscopy cases; and just 4 (3.3%) cases underwent more than 3 laryngoscopy attempts who considered as difficult intubation cases. The mean age of the patients in non-difficult and difficult intubation groups were 69.2 ± 15.16 and 68.77 ± 17.37 years, respectively (p > 0.05). There was no significant relationship between difficult laryngoscopy and HBV (p = 0.381) but has significant correlation with difficult intubation (p = 0.004). The DSHB had a significant correlation with difficult laryngoscopy (p = 0.002) but its correlation with difficult intubation was not significant (p = 0.629). The DSVC and DSTI had a significant relationship with both difficult laryngoscopy (p = 0.003 and p = 0.001), and difficult intubation (p = 0.025 and p = 0.001). The DBAC had not significant correlation neither with the difficult laryngoscopy (p = 0.142), nor with difficult intubation (p = 0.526).

CONCLUSION

The findings showed that ultrasound parameters including soft tissue DSHB, DSVC and DSTI could be proper predictors of difficult laryngoscopy. Also, HBV, DSVC and DSTI may be proper predictors for difficult intubation. But DBAC was not useful in this regard.

Effectiveness and Validity of Preoperative Ultrasonographic Airway Assessment and Clinical Screening Tests to Predict Difficult Laryngoscopy: A Prospective, Observational Study

BACKGROUND

The anticipation of a challenging airway can be demanding in emergency care settings. Due to the patient's clinical condition, executing the pre-intubation clinical screening tests during the management of the airway in an emergency situation can be sometimes troublesome. Ultrasonographic airway assessment may become a helpful tool, but no specific sonographic measurements can precisely visualize the prospect of meeting a difficult airway. Therefore, the present study aimed to verdict some correlation between preoperative sonographic airway assessment parameters and the Cormack-Lehane (CL) grading at laryngoscopic view in patients undergoing general anesthesia with endotracheal intubation.

METHODS

This observational study was conducted on 150 elective surgery subjects undergoing general anesthesia. The clinician in the pre-anesthetic clinic performed clinical airway and ultrasonographic airway assessments to predict difficult intubation and correlated with the CL grade viewed at laryngoscopy in the operative room during intubation. The parameters assessed were sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV).

RESULTS

In this study, the incidence of difficult intubation was 13.3%. The Mallampatti Grading (MPG) showed the maximum receiver operating characteristic (ROC) and area under the curve (AUC) among the clinical predictors, with 86.7% sensitivity. At the same time, the skin-to-hyoid distance has the maximum ROC among the sonographic parameters, and the skin-to-thyroid isthmus has the utmost sensitivity to predict difficult laryngoscopy.

CONCLUSIONS

Among the clinical predictors, MPG and the sonographic parameters, like the skin-to-hyoid distance and skin-to-thyroid isthmus, are favorable predictors of difficult laryngoscopy.

Pre-operative ultrasound prediction of difficult airway management in adult patients: A systematic review of clinical evidence

BACKGROUND

Predicting a difficult airway, including difficult laryngoscopy, intubation or mask ventilation, is paramount in peri-operative management. As clinical predictors are only partially reliable, ultrasound-based measurements might be useful in evaluating anterior neck fat tissues depth.

OBJECTIVES

The aim of this systematic review is to report clinical evidence on pre-operative ultrasound as a predictor of difficult laryngoscopy, difficult intubation or difficult mask ventilation.

DESIGN

A systematic review of randomised controlled trials and observational studies.

DATA SOURCES

The MEDLINE, EMBASE and Google Scholar databases were queried from inception until 28 February 2022.

ELIGIBILITY CRITERIA

Studies involving adult patients who had undergone orotracheal intubation after evaluation with airways ultrasound were considered suitable. Exclusion criteria were a clinical history of difficult airways, cancer or trauma, pregnancy, supraglottic airway devices, video-laryngoscopy. Parameters were classified by reporting their accuracy in discriminating 'difficult' vs. 'not difficult' laryngoscopy, intubation or mask ventilation.

RESULTS

Thirty-one observational studies were included and a total of 41 single parameters and 12 different combinations of clinical and ultrasound parameters were reported. The distance from skin to epiglottis midway with neutral position of head and neck, the distance from hyoid bone to skin surface with a neutral position of head and neck and the hyomental distance extended/neutral ratio are the most associated with difficult laryngoscopy or difficult intubation. A combination of clinical and ultrasound parameters (a modified Mallampati score, the distance from the skin to the epiglottis midway with neutral position of the head and neck, and the USED-MSH score) showed high accuracy. Only two studies reported the role of ultrasound in predicting difficult mask ventilation: the distance from hyoid bone to skin surface with neutral position of head and neck, the thickness of the base of the tongue with hyperextension of the head, and the hyomental distance with hyperextension of the head and active subluxation of the mandible are the parameters with the highest correlation.

CONCLUSIONS

The use of ultrasound parameters might be useful in predicting difficult laryngoscopy or difficult intubation. Several ultrasound parameters and combinations have been associated with difficult laryngoscopy or difficult intubation prediction. The use of scores combining clinical predictors and ultrasound measures are very promising. Data on difficult mask ventilation are scarce and the role of ultrasound is still controversial. Future studies are needed.

CLINICAL TRIAL REGISTRATION

CRD42021250574.

Airway ultrasound for patients anticipated to have a difficult airway: Perspective for personalized medicine

Airway ultrasound allows for precise airway evaluation, particularly for assessing the difficult airway and the potential for front of neck access. Many studies have shown that identification of the cricothyroid membrane by airway ultrasound is more accurate than digital palpation. However, no reports to date have provided clinical evidence that ultrasound identification of the cricothyroid membrane increases the success rate of cricothyroidotomy. This is a narrative review which describes patients with difficult airways for whom airway ultrasound may have been useful for clinical decision making. The role of airway ultrasound for the evaluation of difficult airways is summarized and an approach to the use of ultrasound for airway management is proposed. The goal of this review is to present practical applications of airway ultrasound for patients predicted to have a difficult airway and who undergo cricothyroidotomy.

Evaluation of thyromental height test in prediction of difficult airway in obese surgical patients: An observational study

BACKGROUND AND AIMS

Thyromental height test (TMHT) has revealed good potentials for predicting difficult laryngoscopy view (DLV) in non-obese patients, but its accuracy in obese patients is not evident. This study aimed to assess the validity of TMHT as a predictor of DLV in obese surgical patients.

METHODS

105 patients, aged 18-60 years, with body mass index (BMI) >30 kg/m², scheduled for elective surgeries under general anaesthesia with an endotracheal tube inserted using conventional laryngoscope were included. Airway was assessed with TMHT, modified Mallampati test (MMT), neck circumference (NC) and NC/TMHT ratio. The DLV was defined as Cormack-Lehane grade ≥3. The primary endpoint was the validity of TMHT as a predictor of DLV. The secondary endpoints were to compare the accuracy of TMHT with that of the NC, MMT and NC/TMHT ratio as predictors of the difficult airway.

RESULTS

The BMI was 43.7 ± 6.6 kg/m². The DLV cases were 23/105 (21.9%). The MMT, TMHT and NC/TMHT ratio had the best predictive ability of DLV with areas under receiver operating characteristic curve of 0.91, 0.92 and 0.80; at cut-off values >2, <47 mm and >7.9, respectively. MMT and TMHT were the only predictors of DLV by multivariate analysis.

CONCLUSION

In obese surgical patients, TMHT is an excellent predictor of DLV when the cut-off value is <47 mm.

Evaluation of a novel emergency front of neck access device in a benchtop model of obesity

BACKGROUND

Emergency front of neck access (eFONA) is a critical step in oxygenation in cases of unrelieved airway obstruction. Multiple techniques are used in clinical practice without agreement regarding the optimal approach. We evaluated a novel device, the Cric-Guide (CG), a channelled bougie introducer that enters the airway in a single action and compared it with a scalpel-bougie-tube (SBT) technique in laboratory benchtop model.

METHODS

Seven anaesthesiologists attempted eFONA on both obese and non-obese models using both techniques in randomized order on an excised porcine trachea with an intact larynx with variable subcutaneous tissue depth. The primary outcome was successful tracheal cannulation. Secondary outcomes included false passage rate, time and tissue injury.

RESULTS

Anaesthesiologists performed 4 cricothyroidotomies on each model with each device. The CG was more successful in airway cannulation (47/56 [89.4%] vs. 33/56 [58.9%], P = 0.007). This difference was observed in the obese model only. The CG was associated with fewer false passages than the standard technique in the obese model (8/56 [14.3%] vs. 23/56 [41.1%], P = 0.006). There were no significant differences in time to completion or injury patterns between the techniques in the obese model, but the SBT was faster in the non-obese model. There was no difference in the proportion of specimens injured.

CONCLUSION

The Cric-Guide device was more successful than the standard SBT technique in airway cannulation in an obese neck model and with equivalent frequency and distribution of injury but performed equivalently in the non-obese model.

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.

Comparison of Airway Ultrasound Indices and Clinical Assessment for the Prediction of Difficult Laryngoscopy in Elective Surgical Patients: A Prospective Observational Study

Background:

Ultrasound is evolving as a probable tool in airway assessment. The upper airway is a superficial structure and has sonographically identifiable structures which makes it ideal for evaluation with the ultrasound.

Aims:

The aim of this study was to evaluate the role of skin to hyoid and skin to thyrohyoid membrane distance in prediction of difficult laryngoscopy.

Settings and Design:

This is a prospective observational study included 150 patients aged 18–60 years of American Society of Anesthesiologists Physical Status I and II scheduled to undergo surgery under general anesthesia requiring laryngoscopy and endotracheal intubation.

Materials and Methods:

The modified Mallampati score, mouth opening, mentohyoid distance, thyromental distance were noted. Skin to hyoid bone distance and skin to thyrohyoid membrane distance were measured by ultrasound. Patients were clubbed retrospectively into easy and difficult laryngoscopy groups on the basis of Cormack Lehane grading, and the characteristics of both groups were compared.

Statistical Analysis:

Statistical Package for the Social Sciences, Version 23 was used for statistical analysis. Independent samples t-test was used to compare the means between difficult and easy laryngoscopy patients. Diagnostic accuracy of the significant (P < 0.05) variables between difficult and easy laryngoscopy patients was calculated using receiver operating characteristics curve in terms of their area under curve. Appropriate cutoff values (with corresponding sensitivity, specificity, and overall accuracy) were also identified.

Results:

Out of 150 patients, 13 (8.7%) were identified as difficult laryngoscopy whereas 137 patients (91.3%) were identified as easy laryngoscopy. The demographics of both groups were comparable. Mentohyoid distance, skin to hyoid bone distance, and skin to thyrohyoid distance were statistically different between easy and difficult laryngoscopy patients, with lower mentohyoid distance and higher skin to hyoid bone distance and skin to thyrohyoid distance in difficult laryngoscopy patients. Diagnostic accuracy of the mentohyoid distance (70.3%) was slightly superior to skin to hyoid bone distance (67.1%) and skin to thyrohyoid distance (68.1%).

Conclusion:

Ultrasound measurements of skin to hyoid bone and skin to thyrohyoid membrane distance fail to eclipse clinical parameters in accurately predicting a difficult laryngoscopy.

Submental Ultrasound Is Effective in Predicting Difficult Mask Ventilation but Not in Difficult Laryngoscopy

The goal of this study was to determine the utility of submental ultrasound parameters in distinguishing difficult airway management from easy airway management. Forty-one adult patients who underwent elective surgery under general anesthesia with endotracheal intubation from March to December 2018 were included. We used submental ultrasound to measure tongue base thickness (TBT) in the midsagittal plane and the distance between lingual arteries (DLA) in the transverse dimension. The primary outcome was difficult laryngoscopy, and the secondary outcome was difficult mask ventilation. Receiver operating characteristic curve analysis and logistic regression revealed no correlation between difficult laryngoscopy and SMUS measurements. Nevertheless, patients with difficult mask ventilation had significantly higher TBT (p = 0.009) and longer DLA (p = 0.010). After adjustment of confounding factors, increased TBT (>69.6 mm) was the sole independent predictor of difficult mask ventilation. The results indicated that SMUS is effective in predicting difficult mask ventilation but not difficult laryngoscopy.

Comparative Study of Clinical and Ultrasound Parameters for Defining a Difficult Airway in Patients with Obesity

INTRODUCTION

Patients with obesity have anatomical changes due to increased adipose tissue that negatively affect airway accessibility, making it difficult to establish an advanced airway through orotracheal intubation. This article aims to evaluate the correlation of clinical and sonographic parameters as predictors of difficult airway management (DAM) in patients with obesity and to establish the predictive value of the skin-epiglottis distance as an indicator of a probable DAM.

METHODS

This is an observational, prospective study of 100 patients with obesity who underwent bariatric surgery over a 12-month period. The patients were categorized into the easy airway and the difficult airway groups, according to the Cormack-Lehane classification in the laryngoscopy evaluation, and the clinical and sonographic variables collected were statistically evaluated to obtain the relation with the presence of DAM, according to the Cormack-Lehane classification.

RESULTS

The mouth opening (p = 0.010) and the skin-epiglottis distance (p = 0.019) were statistically significant when comparing the easy airway and the difficult airway groups of the Cormack-Lehane classification. The predictive value of the skin-epiglottis distance for difficult airway assessment was 29.3 mm. The neck circumference (p = 0.225), the Mallampati index (p = 0.260), and the other clinical variables showed no statistical relevance when compared in isolation with the Cormack-Lehane groups.

CONCLUSION

The ultrasound method as a predictor of difficult intubation is promising in anesthetic practice when used according to standardized measurements evaluation and cutoff values.

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.

Useful Ultrasonographic Parameters to Predict Difficult Laryngoscopy and Difficult Tracheal Intubation-A Systematic Review and Meta-Analysis

Unexpected difficult airway management can cause significant morbidity and mortality in patients admitted for elective procedures. Ultrasonography is a promising tool for perioperative airway assessment, nevertheless it is still unclear which sonographic parameters are useful predictors of difficult laryngoscopy and tracheal intubation. To determine the ultrasonographic predictors of a difficult airway that could be applied for routine practice, a systematic review and meta-analysis was conducted. Literature search was performed on PubMED, Web of Science and Embase using the selected keywords. Human primary studies, published in English with the use of ultrasonography to prediction of difficult laryngoscopy or tracheal intubation were included. A total of 19 articles (4,570 patients) were analyzed for the systematic review and 12 articles (1,141 patients) for the meta-analysis. Standardized mean differences between easy and difficult laryngoscopy groups were calculated and the parameter effect size quantified. A PRISMA methodology was used and the critical appraisal tool from Joanna Briggs Institute was applied. Twenty-six sonographic parameters were studied. The overall effect of the distance from skin to hyoid bone (p = 0.02); skin to epiglottis (p = 0.02); skin to the anterior commissure of vocal cords (p = 0.02), pre-epiglottis space to distance between epiglottis and midpoint between vocal cords (p = 0.01), hyomental distance in neutral (p < 0.0001), and extended (p = 0.0002) positions and ratio of hyomental distance in neutral to extended (p = 0.001) was significant. This study shows that hyomental distance in the neutral position is the most reliable parameter for pre-operative airway ultrasound assessment. The main limitations of the study are the small sample size, heterogeneity of studies, and absence of a standardized ultrasonographic evaluation method [Registered at International prospective register of systematic reviews (PROSPERO): number 167931].

Diagnostic Accuracy of Ultrasound Measurements of Anterior Neck Soft Tissue in Determining a Difficult Airway

Context:

Airway management in the emergency department is challenging because conventional screening tools cannot be applied. Therefore, a rapid noninvasive means of identifying a difficult airway will be advantageous for emergency physicians.

Aims:

The aim of this study is to examine the association between ultrasound measurements of anterior neck soft tissue and difficult airway as judged by the Cormack Lehane grading.

Settings and Design:

A prospective study was done for 18 months on patients requiring intubation presenting to the emergency medicine department.

Subjects and Methods:

Ultrasound measurements of anterior neck soft tissue were obtained in 60 cases at the levels of thyrohyoid membrane, hyoid bone, and vocal cords. Another examiner who was blinded to the ultrasound measurements performed endotracheal intubation and noted Cormack–Lehane grading.

Statistical Analysis Used:

Descriptive statistics such as mean, standard deviation, frequency, and percentage were used. Inferential statistics such as Student's t-test and receiver operating characteristic (ROC) curve analysis were done using the SPSS software version 22.

Results:

The thickness of anterior neck soft tissues at the level of hyoid bone in difficult patients was 0.73 cm (95% confidence interval = 0.65–0.80) compared to easy patients 0.47 cm (95% confidence interval = 0.44–0.51) with a P = 0.001 and at the level of thyrohyoid membrane in difficult patients it was 1.83 cm (95% confidence interval = 1.7–1.89) compared to easy patients 1.46 cm (95% confidence interval = 1.41–1.51) with a P = 0.001. Area under the ROC curve was significant at all the three levels with the highest at the level of thyrohyoid membrane 0.99 and least at the level of vocal cords 0.79, the area under the curve was 0.92 at the level of hyoid bone.

Conclusions:

Sonographic measurements of the anterior neck soft tissue can be used as a screening tool by an emergency physician to detect difficult intubation.

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.

Airways ultrasound in predicting difficult face mask ventilation

BACKGROUND

Unanticipated difficult airway is a potentially life-threatening event during elective surgery or management of critical conditions. Nevertheless, predicting difficult mask ventilation currently remains a challenge due to the poor sensitivity of available clinical tests. Our primary goal was to verify whether preoperative upper airway ultrasound measurements were useful to predict difficult face mask ventilation. Our secondary goal was to evaluate clinical characteristics and differences between patients who are difficult to ventilate and patients who are not.

METHODS

We performed a prospective observational study, enrolling 250 adult patients selected for colorectal, gastric, bariatric and pancreatic elective surgery between September 2017 and October 2018. We performed a preoperative US assessment of the airways, following a standardized protocol. We measured the hyomental distance (DIM), the thickness of the base of the tongue (SBL), the thickness of the soft tissues anterior to the hyoid bone (STTi), thyro-hyoid distance (DTI), the thickness of soft tissue anterior to the epiglottis (STTe), to the arytenoid (STTa) and to the commissure of the vocal cords (STTcv).

RESULTS

SBL had a predictive role of difficult mask ventilation in curarized and noncurarized patients for values higher than 50 mm. Hyomental distance with hyperextension of the head and subluxation of the mandible (DIMs) had a predictive role in the curarized patient (protective parameter).

CONCLUSIONS

Airways ultrasound evaluation could be an important tool to predict difficult mask ventilation. Further studies are necessary to validate the parameters found and correlate them to the preoperative clinical evaluation.

Ultrasound measurement of laryngeal structures in the parasagittal plane for the prediction of difficult laryngoscopies in Chinese adults

Background

Abnormal laryngeal structures are likely to be associated with a difficult laryngoscopy procedure. Currently, laryngeal structures can be measured by ultrasonography, however, little research has been performed on the potential role of ultrasound on the evaluation of a difficult laryngoscopy. The present study investigated the value of laryngeal structure measurements for predicting a difficult laryngoscopy.

Objective

The main objective of this study was to explore the value of laryngeal structure measurements for predicting a difficult laryngoscopy.

Methods

Two hundred and eleven adult patients (over 18 years old) were recruited to undergo elective surgery under general anesthesia via endotracheal intubation. Ultrasound was utilized to measure the distance between the skin and thyroid cartilage (DST), the distance between the thyroid cartilage and epiglottis (DTE), and the distance between the skin and epiglottis (DSE) in the parasagittal plane. These metrics were then investigated as predictors for classifying a laryngoscopy as difficult vs easy, as defined by the Cormack and Lehane grading scale.

Results

Multivariate logistic regression showed that the DSE, but not DST or DTE, was significantly related to difficult laryngoscopies. Specifically, a DSE ≥ 2.36 cm predicted difficult laryngoscopies with a sensitivity and specificity of 0.818 (95% CI: 0.766–0.870) and 0.856 (95% CI: 0.809–0.904). Furthermore, when combining the best model constructed of other indicators (i.e. sex, body mass index, modified Mallampati test) to predict the difficult laryngoscopy, the AUC reached 93.28%.

Conclusion

DSE is an independent predictor of a difficult laryngoscopy; a DSE cutoff value of 2.36 cm is a better predictor of a difficult laryngoscope than other ultrasound or physiological measurements for predicting a difficult laryngoscope. Nevertheless, it’s more valuable to apply the best model of this study, composed of various physiological measurements, for this prediction purpose.

Ultrasound for diagnosing new difficult laryngoscopy indicator: a prospective, self-controlled, assessor blinded, observational study

Background:

Unpredictable difficult laryngoscopy (DL) remains a challenge for anesthesiologists, especially when difficult ventilation occurs during standard laryngoscopy. Accurate airway assessment should always be performed, but the common airway assessment methods only perform superficial screening. Thus, the deep laryngopharyngeal anatomy may not be evaluated. Ultrasound-based airway assessment has been recently proposed as a useful, simple, and non-invasive bedside tool as an adjunct to clinical methods, which may facilitate identification of DL. The present study aimed to determine the correlation between ultrasound-measured indicators and DL.

Methods:

Patients undergoing elective surgery under general anesthesia with tracheal intubation were enrolled. Ultrasonic airway assessments were performed before anesthesia induction. Ultrasound diagnostic indicators included the thickness and width of the base of the tongue, the angle between the epiglottis and glottis, the length of the thyrohyoid membrane, and the thickness of the lateral pharyngeal wall. A score of ≥3 in the Modified Cormack-Lehane Scoring System was used as a standard of DL and was also applied to divide patients into DL and non-DL groups. The area under the receiver operating characteristic (ROC) curve was used to evaluate the diagnostic ability of various diagnostic indicators.

Results:

A total of 499 patients were enrolled into non-DL and DL groups comprising 452 (452/499, 90.6%) and 47 (47/499, 9.4%) patients, respectively. One ultrasonic diagnoses indicator correlated with DL, namely, the angle between the epiglottis and glottis. When the angle between the epiglottis and glottis was 50°, the area under the ROC curve was maximum (0.902), and the best sensitivity (81%) and specificity (89%) were achieved.

Conclusions:

Airway ultrasounds should be considered to identify DL. The ultrasonic angle measured between the epiglottis and glottis is highly associated with DL, which may occur when the angle is less than 50°.

Clinical trial registration:

ChiCTR-DDT-13004102, http://www.chictr.org.cn/showproj.aspx?proj=5465

Ultrasonography for predicting a difficult laryngoscopy. Getting closer

Our objective was to evaluate the usefulness of five ultrasound measurements to predict a difficult laryngoscopy (DL). Prospective observational study. 50 patients underwent scheduled surgery under general anesthesia with orotracheal intubation with classical laryngoscopy at the University Hospital of Jaén (Spain). Sociodemographic variables, classic preintubation screening tests and ultrasound measurements of the neck soft tissue from skin to hyoid (DSH), epiglottis (DSE) and glottis (DSG) were obtained, as well as two measurements derived from the above: DSH + DSE and DSE - DSG. The relationship between a DL and ultrasound measurements was evaluated using t student test. The ROC Curve was used to establish the diagnostic accuracy of ultrasound measurements to discriminate a DL and logistic regression was used to establish a cut-off point. Multivariate analysis was performed to assess the impact of these measures in clinical practice. Patients with DL showed greater thickness of DSE (2.9 ± 0.46 cm vs 2.32 ± 0.54 cm; p = 0.001), DSH + DSE (4.25 ± 0.45 cm vs 3.62 ± 0.77 cm; p = 0.001) and DSE - DSG (1.83 ± 0.54 cm vs 1.24 ± 0.46 cm; p = 0.001) than those with an easy laryngoscopy. DSE and DSE - DSG had the highest diagnostic accuracy for DL with an area under the ROC curve of 0.79 [95%IC 0.66-0.92] and 0.82 [95%IC 0.68-0.96], respectively. It was established that DSE ≥ 3 cm, could predict a DL with a positive predictive value (PPV) of 69.23% [95%CI 40.3-98.2], and DSE - DSG ≥ 1.9 cm would do so with a PPV of 78.57% [95%CI 53.31-100%]. The multivariate analysis endorsed that DSE and DSE - DSG combined with classic tests (the Modified Mallampati score, the thyromental distance and the upper lip bite test) improved the preoperative detection of a DL. The inclusion of DSE and DSE - DSG in a multivariate model with classic parameters may offer the anesthesiologist better information for detecting a DL preoperatively.

Anterior neck soft tissue thickness for airway evaluation measured by MRI in patients with cervical spondylosis: prospective cohort study

OBJECTIVES

Anterior neck soft tissue thickness, usually measured by ultrasound, is increasingly being investigated to predict difficult laryngoscopy, but the results have not been validated. Considering the conflicting measurement data, different measuring body positions and lack of a standard ultrasound procedure, we used MRI to verify the efficacy of these popular ultrasonographic parameters.

DESIGN

Prospective cohort study.

SETTING

A tertiary hospital in Beijing, China.

METHODS

We enrolled 315 adult patients who underwent cervical spinal surgery in Peking University Third Hospital from April to October 2016. We analysed MRI data to predict difficult laryngoscopy. Cormack-Lehane scales were assessed during intubation, and patients with a class III or IV view were assigned to the difficult laryngoscopy group.

RESULTS

Univariate analysis showed that male sex (p<0.01), older age (p=0.03) and body weight (p=0.02) were associated with difficult laryngoscopy. MRI data consisted of five common ultrasonographic variables used to predict difficult laryngoscopy, but none was a valuable predictor: skin to hyoid (p=0.18), skin to midpoint of epiglottis (p=0.72), skin to thyroid cartilage at the level of the vocal cords (p=0.10), skin to vocal cords (p=0.44) or skin to anterior to the trachea at the level of suprasternal notch (p=0.92). Adjusted by sex, age and body weight, none of the five MRI indicators had predictive value (p>0.05).

CONCLUSION

The five most commonly studied ultrasonographic indicators of anterior soft tissue thickness appeared unreliable to predict difficult laryngoscopy in patients with cervical spondylosis. Further study is needed to validate the most valuable indicator to predict difficult laryngoscopy.

TRIAL REGISTRATION NUMBER

ChiCTRROC-16008598; Pre-results.

Ultrasound measurement of anterior neck soft tissue and tongue thickness to predict difficult laryngoscopy - An observational analytical study

Background and Aims:

Airway ultrasound is an emerging tool to predict difficult laryngoscopy. This study aimed to determine the utility of ultrasound measurement of the anterior soft tissue neck thickness at the level of hyoid, thyrohyoid membrane and thickness of tongue to predict difficult laryngoscopy and compare them with clinical parameters for airway assessment.

Methods:

The distance from skin to hyoid bone, skin to the thyrohyoid membrane in neutral and sniffing position and maximum tongue thickness was measured by ultrasound and correlated with Cormack Lehane (CL) laryngoscope view in 310 adult surgical patients. Receiver operating characteristic curve was plotted and the area under the curve was calculated for each parameter. The sensitivity and specificity of ultrasound-guided parameters were compared with clinical parameters like the inter-incisor gap, modified Mallampatti classification, thyromental, sternomental distance and neck circumference.

Results:

Incidence of difficult laryngoscopy (CL grade-III and IV) was 11.3%. A significant difference was observed in the ultrasound parameters between the easy and difficult laryngoscopy (P-value = 0.001). Sensitivity and specificity to predict difficult airway was 69.6% and 77% for tongue thickness, 68% and 73% for the skin to hyoid bone distance in a neutral position and found to be higher than clinical parameters.

Conclusion:

The ultrasound measurements of soft tissue thickness of the anterior neck and tongue thickness along with the clinical assessment of airway can be useful in predicting difficult laryngoscopy.

Ultrasound measurement of anatomical parameters of the upper airway in adults

BACKGROUND

Most of the works on ultrasound airway anatomy are limited to a morphological description. A study was conducted in order to provide an objective normal range of measurements.

MATERIALS AND METHODS

Observational study to describe the ultrasound characteristics of the upper airway in adults without clinical difficult airway criteria, compared to cadaver dissection anatomical models.

RESULTS

The study included 45 volunteers (27 men and 18 women), and 3fresh cadavers. The quality of the examination was very good/good in 93% of the cases.

MEASUREMENTS

tracheal diameter (1.3±0.3cm), vocal cord (1.6±0.5cm), cricothyroid membrane (0.94±0.32cm), cricotracheal membrane (0.3±0.09cm), thickness of the muscles in the floor of the mouth (MFM) (1.5±0.26cm), sub-mandibular subcutaneous fat plus MFM (2.11±0.34cm), hyoid-mandible distance (5.35±0.69cm), palate-floor of the mouth distance (4.92±0.5cm), palate-anterior border of the mandible (5.51±0.7cm), and palate-pharynx angle (114±14). Observed differences: Males had a larger tracheal diameter than females (M: 1.4±0.3 vs. F: 1.2±0.2cm, p=0.014). Subject height showed a significant correlation with the tracheal diameter (R: 0.501, p<0.001), as well as the length of the vocal cord (R: 0.363, p=0.016), the thickness of MFM (R=0.299, p=0.046) as well as the hyoid-mandible (R: 0.556; p<0.001) and palate-mandible distances (R: 0.362; p=0.015).

CONCLUSIONS

Ultrasound allows the anatomy of upper airway to be evaluated, as well as to calculate distances between the anatomical structures. The study defines these distances in adult volunteers without clinical difficult airway criteria.

[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.

Airway physical examination tests for detection of difficult airway management in apparently normal adult patients

BACKGROUND

The unanticipated difficult airway is a potentially life-threatening event during anaesthesia or acute conditions. An unsuccessfully managed upper airway is associated with serious morbidity and mortality. Several bedside screening tests are used in clinical practice to identify those at high risk of difficult airway. Their accuracy and benefit however, remains unclear.

OBJECTIVES

The objective of this review was to characterize and compare the diagnostic accuracy of the Mallampati classification and other commonly used airway examination tests for assessing the physical status of the airway in adult patients with no apparent anatomical airway abnormalities. We performed this individually for each of the four descriptors of the difficult airway: difficult face mask ventilation, difficult laryngoscopy, difficult tracheal intubation, and failed intubation.

SEARCH METHODS

We searched major electronic databases including CENTRAL, MEDLINE, Embase, ISI Web of Science, CINAHL, as well as regional, subject specific, and dissertation and theses databases from inception to 16 December 2016, without language restrictions. In addition, we searched the Science Citation Index and checked the references of all the relevant studies. We also handsearched selected journals, conference proceedings, and relevant guidelines. We updated this search in March 2018, but we have not yet incorporated these results.

SELECTION CRITERIA

We considered full-text diagnostic test accuracy studies of any individual index test, or a combination of tests, against a reference standard. Participants were adults without obvious airway abnormalities, who were having laryngoscopy performed with a standard laryngoscope and the trachea intubated with a standard tracheal tube. Index tests included the Mallampati test, modified Mallampati test, Wilson risk score, thyromental distance, sternomental distance, mouth opening test, upper lip bite test, or any combination of these. The target condition was difficult airway, with one of the following reference standards: difficult face mask ventilation, difficult laryngoscopy, difficult tracheal intubation, and failed intubation.

DATA COLLECTION AND ANALYSIS

We performed screening and selection of the studies, data extraction and assessment of methodological quality (using QUADAS-2) independently and in duplicate. We designed a Microsoft Access database for data collection and used Review Manager 5 and R for data analysis. For each index test and each reference standard, we assessed sensitivity and specificity. We produced forest plots and summary receiver operating characteristic (ROC) plots to summarize the data. Where possible, we performed meta-analyses to calculate pooled estimates and compare test accuracy indirectly using bivariate models. We investigated heterogeneity and performed sensitivity analyses.

MAIN RESULTS

We included 133 (127 cohort type and 6 case-control) studies involving 844,206 participants. We evaluated a total of seven different prespecified index tests in the 133 studies, as well as 69 non-prespecified, and 32 combinations. For the prespecified index tests, we found six studies for the Mallampati test, 105 for the modified Mallampati test, six for the Wilson risk score, 52 for thyromental distance, 18 for sternomental distance, 34 for the mouth opening test, and 30 for the upper lip bite test. Difficult face mask ventilation was the reference standard in seven studies, difficult laryngoscopy in 92 studies, difficult tracheal intubation in 50 studies, and failed intubation in two studies. Across all studies, we judged the risk of bias to be variable for the different domains; we mostly observed low risk of bias for patient selection, flow and timing, and unclear risk of bias for reference standard and index test. Applicability concerns were generally low for all domains. For difficult laryngoscopy, the summary sensitivity ranged from 0.22 (95% confidence interval (CI) 0.13 to 0.33; mouth opening test) to 0.67 (95% CI 0.45 to 0.83; upper lip bite test) and the summary specificity ranged from 0.80 (95% CI 0.74 to 0.85; modified Mallampati test) to 0.95 (95% CI 0.88 to 0.98; Wilson risk score). The upper lip bite test for diagnosing difficult laryngoscopy provided the highest sensitivity compared to the other tests (P < 0.001). For difficult tracheal intubation, summary sensitivity ranged from 0.24 (95% CI 0.12 to 0.43; thyromental distance) to 0.51 (95% CI 0.40 to 0.61; modified Mallampati test) and the summary specificity ranged from 0.87 (95% CI 0.82 to 0.91; modified Mallampati test) to 0.93 (0.87 to 0.96; mouth opening test). The modified Mallampati test had the highest sensitivity for diagnosing difficult tracheal intubation compared to the other tests (P < 0.001). For difficult face mask ventilation, we could only estimate summary sensitivity (0.17, 95% CI 0.06 to 0.39) and specificity (0.90, 95% CI 0.81 to 0.95) for the modified Mallampati test.

AUTHORS' CONCLUSIONS

Bedside airway examination tests, for assessing the physical status of the airway in adults with no apparent anatomical airway abnormalities, are designed as screening tests. Screening tests are expected to have high sensitivities. We found that all investigated index tests had relatively low sensitivities with high variability. In contrast, specificities were consistently and markedly higher than sensitivities across all tests. The standard bedside airway examination tests should be interpreted with caution, as they do not appear to be good screening tests. Among the tests we examined, the upper lip bite test showed the most favourable diagnostic test accuracy properties. Given the paucity of available data, future research is needed to develop tests with high sensitivities to make them useful, and to consider their use for screening difficult face mask ventilation and failed intubation. The 27 studies in 'Studies awaiting classification' may alter the conclusions of the review, once we have assessed them.

Correlation of Neck Circumference with Difficult Mask Ventilation and Difficult Laryngoscopy in Morbidly Obese Patients: an Observational Study

PURPOSE

Mask ventilation and laryngoscopy can be challenging in morbidly obese patients because of excessive fat tissue. There are studies suggesting that neck circumference is associated with difficult mask ventilation, difficult laryngoscopy, and difficult intubation. The primary aim of our study is to evaluate predictive value of neck circumference for difficult mask ventilation and difficult laryngoscopy in female and male morbidly obese patients separately.

METHODS

This observational cross-sectional study was performed in the period between March 2015 and December 2015. One hundred and twenty (37 male and 83 female) patients undergoing elective surgery were included. Neck circumference, BMI, Mallampati scores, neck movements, dentition, upper lip bite test, breast, thorax, waist, hip circumferences, mouth opening, and sternomental and thyromental distances were evaluated preoperatively. Mask ventilation was graded using four-grade classification. Laryngoscopy was evaluated by Cormack Lehane score.

RESULTS

The incidence of difficult mask ventilation was 13.5% in male and 3.6% in female patients. Mouth opening ≤ 6.5 cm and inadequate flexion were found as significant predictors for difficult mask ventilation in male patients. The incidence of difficult laryngoscopy was 10.8% in male and 4.8% in female patients. Mallampati score > II was found as a significant predictor for difficult laryngoscopy in both male and female patients. Sternomental distance ≤ 16 cm and inadequate flexion were also significant predictors for difficult laryngoscopy in male patients. Neck circumference was not found statistically significant predictor for difficult mask ventilation and laryngoscopy in morbidly obese patients in our study.

CONCLUSION

Neck circumference is not a statistically significant predictor for difficult mask ventilation and laryngoscopy in morbidly Turkish obese male and female patients.

CLINICAL TRIALS REGISTRATION NUMBER

NCT02589015.