Use of ultrasound to predict difficult intubation in Chinese population by assessing the ratio of the pre‐epiglottis space distance and the distance between epiglottis and vocal folds

Abstract

Objective: To investigate the accuracy of using the ratio of pre-epiglottis space distance (Pre-E) and the distance between the epiglottis and the vocal folds (Pre-E/E-VF) measured by the ultrasound to predict potential difficult airway in the Chinese population. Design: A prospective clinical study. Setting: The pre-operative assessment service clinic of Tuen Mun Hospital. Patients: Patients with age of 18 years or above, who were scheduled for elective surgery requiring general anesthesia with direct laryngoscopy and tracheal intubation. Results: A total of 113 patients with direct laryngoscopic assessment during elective operations were included. Thirty-nine (34.5%) patients had potential difficult airway which was defined as documented Cormack-Lehane classification grade 2b, 3, or 4 by the anesthetists. Measurement of the distance from the epiglottis to the anterior vocal folds (Pre-E/aVF) ratio had better inter-rater reliability and accuracy comparing to the measurements of the distances from the epiglottis to the midpoint between the vocal folds and to the posterior vocal folds. The performance of using the Pre-E/aVF ratio to predict potential difficult airway was compared with other clinical tests (the Mallampati classification, the thyromental distance and the neck circumference to thyromental distance ratio). By using the Pre-E/aVF ratio of 1, the sensitivity and specificity to predict a potential difficult airway were 79.5% and 39.2%, respectively (p = 0.044). The ultrasound assessment method had a comparable predictive value as the Mallampati classification (the area under the receiver operator characteristic curves 0.648 vs 0.687). The negative likelihood ratio of the ultrasound assessment method was the lowest among all the other airway assessment methods.

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

“…The most common exclusion criteria reported were limited neck mobility secondary to cervical spine fractures or tumors (18-22, 24-30), limited neck extention (21,22,29,31,32), including arthritis (24). Patients with maxillofacial fractures or deformities (18, 21, 22, 24, 27-29, 31, 32) or upper airway abnormalities (19,25,26,28,30,(33)(34)(35), including epiglottic surgery (24), limited interincisal distance (20,22,29,31,32), subglottic stenosis (35), or thyroid disease (27,30) were also eliminated from the reported samples.…”

“…In 53% of the studies (19,20,23,24,28,30,(32)(33)(34)(35), laryngoscopy was reportedly performed by experienced anesthetists with more than 2 years of training, although most of the authors (53%) omitted mentioning the number of anesthetists who performed the technique (12,19,20,22,23,27,29,31,32,35).…”

“…Regarding the laryngoscopy classification method, there are some important differences between studies since Chan et al (29) analyzed anesthesia records after surgeries (12), analyzed anesthesia records from previous surgeries, and (18,21,22,28) did not have an anaesthesiologist specifically assigned for this task. Furthermore, Wu et al (24) did not blind the US results and (12, 21-23) did not mention blinding.…”

“…By contrast, evaluation of the pre-epiglottic space (Pre-E) ( 22), distance from epiglottis to midpoint of the distance between vocal cords (E-VC) (22); skin to trachea at the level of the thyroid isthmus (18,25,30); floor of the mouth muscle crosssectional area (33); floor of the mouth muscle volume (12,27); tongue width and tongue thickness-to-oral cavity height ratio (33) and Pre-E/pVC (22,29) were not significant in predicting a difficult laryngoscopy.…”

“…Chan et al (29) found that a Pre-E/aVC ratio superior to 1 (Se: 79.5%; Sp: 39.2%) (29) predicts a difficult laryngoscopy.…”