Table 1.
Summary of studies on ultrasonographic parameters for predicting difficult laryngoscopy or difficult intubation.
| Author, Date, and Country | Setting | Patient Group | Study Design | Outcome Variable | Sample Size | Outcome Count | Key Results |
|---|---|---|---|---|---|---|---|
| Alessandri, 2019, Italy [29] | OR, elective surgery | Italian adults undergoing elective ENT surgery with general anesthesia | Prospective observational | CL grade; Han scale | 194 | Difficult airway = 34 (17.5% incidence) Difficult mask ventilation = 8 (4.1% incidence) |
The best predictor of difficult airway was the minimum distance from the hyoid bone to skin surface |
| Altun, 2021, Turkey [31] | OR, elective surgery | Turkish adults undergoing an elective procedure with general anesthesia | Prospective observational | CL grade | 140 | Difficult laryngoscope = 22 (15.7% incidence) | Significant correlation of US measurements (ESD, HSD, and ToTR) to predict difficult airway, as well as significant correlation of US measurements (MP + HSD or MP + ESD) combined with IL to predict difficult airway (sensitivity 91%, specificity 97%) |
| Ambrose, 2022, India [32] | OR, elective surgery | Indian adults undergoing elective surgery with general anesthesia | Prospective, observational | CL grade | 120 | Difficult intubation = 41 (34.2% incidence) | Distance between skin to epiglottis, tongue thickness, and neck circumference were significantly associated with difficult intubation cases |
| Andruszkiewicz, 2016, Poland [33] | OR, elective surgery | Polish adults undergoing elective surgery | Prospective observational | CL grade | 199 | Difficult laryngoscope = 22 (11.1% incidence) | Strongest predictors were HMD in extension and tongue volume. Significant predictors were (1) HMD in neutral, (2) HMD in extension, (3) HMDR2, (4) tongue cross-sectional area, and (5) tongue volume |
| Agarwal, 2021, India [34] | OR, elective surgery | Indian adults undergoing | Prospective observational | Difficult intubation | 1043 | Difficult to intubate = 58 (5.56% incidence) | Skin to hyoid bone distance was most accurate to predict difficult intubation |
| Bindu, 2022, India [35] | OR, elective surgery | Indian adults with morbid obesity (BMI > 35) undergoing elective surgery with general anesthesia | Prospective observational | CL grade | 70 | Difficult laryngoscopy = 15 (21.4%) | Limited condylar mobility and increased TT were two independent ultrasonographic predictors for difficult direct laryngoscopy |
| Bouzid, 2022, Tunisia [36] | OR, elective surgery | Tunisian adults undergoing general anesthesia | Prospective observational | CL grade; Difficult intubation | 200 | Difficult laryngoscopy = 41 (incidence 20.5%), Difficult intubation = 29 (14.5%) |
A combination of clinical criteria and ultrasound measurements increases the ability to predict difficult airway management |
| Chan, 2018, China [37] | OR, elective surgery | Chinese adults undergoing elective surgery with general anesthesia | Prospective observational | CL grade | 113 | Difficult laryngoscope = 39 (34.5% incidence) | Pre-E/aVF ratio (>1) had better accuracy than pre-E/mVF and pre-E/pVF. Pre-E/E-VC cutoff originally intended to study was too high for the population |
| Daggupati, 2022, India [38] | OR, elective surgery | South Indian adults undergoing elective operation with general anesthesia | Prospective observational | CL grade | 310 | Difficult laryngoscope = 62 (20.0% incidence) | Skin to epiglottis distance via US as part of an airway scoring system (using clinical predictors) was reliable in predicting DA (sensitivity 93%, specificity 85%) |
| Falcetta, 2018, Italy [16] | OR, elective surgery | Italian adults undergoing elective surgery with general anesthesia | Prospective observational | CL grade | 301 | Difficult laryngoscope = 28 (9.3% incidence) | US measured at >2.54 cm and PEA >5.04 cm2 may predict difficult laryngoscopes |
| Falsafi, 2023, Iran [39] | OR, elective surgery | Iranian adults undergoing elective surgery with general anesthesia | Prospective observational | CL grade; Mallampati score | 120 | Difficult laryngoscopy by CL = 34 (28.3% incidence) By Mallampati = 37 (30.8% incidence) |
Neck circumference was significantly correlated with difficult laryngoscopy by CL. HMDN, HMDE, tongue thickness, OCH, and ST were significant by Mallampati |
| Lin, 2021, Taiwan [40] | OR, elective surgery | Taiwanese adults undergoing elective procedure under general anesthesia | Prospective observational | CL grade | 47 | Difficult laryngoscopy = 20 (42.6% incidence) | Submental ultrasound was not predictive in difficult laryngoscopy, only difficult mask ventilation (sensitivity 50%, specificity 87%) |
| Moura, 2021, Brazil [41] | OR, elective surgery (bariatric surgery) | Obese Adults | Prospective observational | CL grade | 100 | Difficult airway = 25 (25% incidence) | Skin to epiglottis distance (29.3 mm) was predictive for difficult intubation (AUC 0.656, sensitivity 66.7%, specificity 66%) |
| Ni, 2020, China [42] | OR, elective surgery | Chinese adults undergoing elective procedures with general anesthesia | Prospective observational | CL grade | 211 | Difficult laryngoscopy = 44 (20.9% incidence) | Significant predictor of difficult laryngoscopies using DSE (sensitivity 81.8%, specificity 85.6%) |
| Prathep, 2022, Thailand [43] | OR, elective surgery | Obese adults in Thailand | Prospective observational | CL grade | 88 | Difficult laryngoscopy = 13 (14.8% incidence) | Scoring model based on US measurements were predictive of difficult laryngoscopy (AUC 0.77) |
| Rana, 2018, India [44] | OR, elective surgery | Indian adults undergoing elective surgery with general anesthesia | Prospective observational | CL grade | 120 | Difficult airway = 28 (23.3% incidence) | Significant predictors were Pre-E/E-VC ratio and HDMR2. Pre-E/E-VC was stronger |
| Reddy, 2016, India [45] | OR, elective surgery | Indian adults undergoing elective surgery with general anesthesia | Prospective observational | CL grade | 100 | Difficult laryngoscope = 14 (14% incidence) | Significant predictors were skin-to-anterior commissure of VC and Pre-E/E-VC ratio |
| Wang, 2019, China [46] | OR, elective surgery | Chinese adults undergoing elective procedures with general anesthesia | Prospective observational | CL grade | 499 | Difficult laryngoscopy = 47 (9.4% incidence) | Angle between the epiglottis and glottis (less than 50 degrees) had the best sensitivity (81%) and specificity (89%) |
| Wang, 2022, China [47] | OR, elective surgery | Chinese adults undergoing elective procedure under general anesthesia | Prospective observational | Cl grade | 2254 | Difficult laryngoscope = 142 (6.3% incidence) Difficult intubation = 51 (2.3% incidence) |
Study nomogram (consisting of US measurements and clinical parameters) had AUC 0.933 for difficult laryngoscopy and 0.974 for difficult intubation |
| Wu, 2014, China [48] | OR, elective surgery | Han Chinese adults aged 20–65, scheduled to undergo general anesthesia | Prospective observational | CL grade | 203 | Difficult laryngoscope = 28 (13.8% incidence) | Independent predictors of difficult airway were the distance from skin to (1) hyoid bone, (2) epiglottis, and (3) anterior commissure of VC |
| Wu, 2022, Taiwan [49] | OR, elective surgery | Taiwanese adults undergoing laparoscopic sleeve gastrectomy | Prospective observational | CL grade | 80 | Difficult laryngoscopy = 17 (21% incidence) | Greater neck circumference was independently associated with difficult laryngoscopy in obese patients. CSA of the tongue base may serve as an index to identify high-risk patients before tracheal intubation |
| Yadav, 2019, India [50] | OR, elective surgery | Indian adults undergoing elective procedures under general anesthesia | Prospective observational | CL grade | 310 | Difficult laryngoscopy = 35 (11.3% incidence) | Tongue thickness as a predictor (sensitivity 69.6%, specificity 77%); skin to hyoid bone distance (sensitivity 68%, specificity 73%) |
| Yao, 2017, China [51] | OR, elective surgery | Han Chinese adults undergoing elective surgery with general anesthesia | Prospective observational | Difficult intubation; CL grade | 2254 | Difficult laryngoscope = 142 (6.3% incidence) Difficult intubation = 51 (2.26% incidence) | Tongue thickness > 6.1 cm is an independent predictor for difficult laryngoscopy (sensitivity 0.75, specificity 0.72). Significant predictors were tongue thickness and tongue thickness/TMD ratio |
| Yao, 2017, China [52] | OR, elective surgery | Han Chinese adults undergoing elective surgery with general anesthesia | Prospective observational | CL grade | 484 | Difficult laryngoscope = 41 (8.5% incidence) Difficult intubation = 5 (1.0% incidence) |
Condylar translation was a significant predictor of difficult laryngoscopy. Condylar translation at ≤1 cm is a meaningful TMJ mobility evaluation predicting difficult laryngoscopy |
| Zheng, 2021, China [53] | OR, elective surgery | Han Chinese adults undergoing elective procedures with general anesthesia | Prospective observational | CL grade | 230 | Difficult laryngoscopy = 28 (12.2% incidence) Difficult intubation = 12 (5.2% incidence) | Midsagittal tongue CSA had highest predictor value for difficult laryngoscopy (sensitivity 71%, specificity 60%) and difficult intubation (sensitivity 39%, specificity 89%) |
Abbreviations: AUC, area under the curve; BMI, body mass index; CL, Cormack-Lehane; CSA, cross-sectional area; DA, difficult airway; DSE, distance from skin to epiglottis; ENT, ear, nose, and throat (otolaryngology); ESD, median distance from skin to epiglottis; HMD, hyomental distance; HMDE, hyomental distance with the head in the extended position; HMDN, hyomental distance with the head in the neutral position; HMDR2, hyomental distance in the extended position to that in the neutral position ratio; HSD, hyoid bone skin distance; OCH, oral cavity height; OR, operating room; PEA, pre-epiglottic area; Pre-E, pre-epiglottic distance; Pre-E/aVF, distance from the epiglottis to the anterior vocal folds; Pre-E/E-VC, ratio of pre-epiglottis space distance (Pre-E) and the distance between the epiglottis and the vocal folds; pre-E/pVC, ratio of pre-epiglottis space to distance between epiglottis and posterior vocal folds; ST, distance from skin to thyroid cartilage; THM, thyrohyoid membrane; TMD, thyromental distance; TMJ, temporomandibular joint; ToTR, thickness of tongue root; TT, tongue thickness; US, ultrasound; VC, vocal cords.