Can thyromental distance be measured accurately?

A quantitative study of airway ultrasound in predicting difficult laryngoscopy: A prospective study

PURPOSE

As common clinical screening tests cannot effectively predict a difficult airway, and unanticipated difficult laryngoscopy remains a challenge for physicians. We herein used ultrasound to develop some point-of-care predictors for difficult laryngoscopy.

METHODS

This prospective observational study included 502 patients who underwent laryngoscopy and a detailed sonographic assessment. Patients under 18 years old, or with maxillofacial deformities or fractures, limited mouth opening, limited neck movement or history of neck surgery were excluded from the study. Laryngoscopic views of all patients were scored and grouping using the modified Cormack-Lehane (CL) scoring system. The measurements acquired comprised tongue width, the longitudinal cross-sectional area of the tongue, tongue volume, the mandible-hyoid bone distance, the hyoid bone-glottis distance, the mandible-hyoid bone-glottis angle, the skin-thyrohyoid membrane distance, the glottis-superior edge of the thyroid cartilage distance (DGTC), the skin-hyoid bone distance, and the epiglottis midway-skin distance. ANOVA and Chi-square were used to compare differences between groups. Logistic regression was used to identify risk factors for difficult laryngoscopy and it was visualized by receiver operating characteristic curves and nomogram. R version 3.6.3 and SPSS version 26.0 were used for statistical analyses.

RESULTS

Difficult laryngoscopy was indicated in 49 patients (CL grade Ⅲ - Ⅳ) and easy laryngoscopy in 453 patients (CL grade Ⅰ - Ⅱ). The ultrasound-measured mandible-hyoid bone-glottis angle and DGTC significantly differed between the 2 groups (p < 0.001). Difficult laryngoscopy was predicted by an area under the curve (AUC) of 0.930 with a threshold mandible-hyoid bone-glottis angle of 125.5° and by an AUC of 0.722 with a threshold DGTC of 1.22 cm. The longitudinal cross-sectional area of the tongue, tongue width, tongue volume, the mandible-hyoid distance, and the hyoid-glottis distance did not significantly differ between the groups.

CONCLUSION

Difficult laryngoscopy may be anticipated in patients in whom the mandible-hyoid bone-glottis angle is smaller than 125.5° or DGTC is larger than 1.22 cm.

Predicting Difficult Intubation: The Hyomental Distance Ultrasound Evaluation is Superior to the Thyromental Distance

BACKGROUND

Hyomental distance (HMD), an anatomical feature of the upper airway, can be measured precisely by ultrasonography. But the sensitivity and specificity of HMD compared to thyromental distance (TMD) to predict difficult airways is still unknown.

METHODS

A cases cohort study was conducted. The written informed consent was obtained. Elective surgery adult patients undergoing general anaesthesia and tracheal intubation were recruited. The other inclusion criteria: no maxillofacial deformity, trauma, airway stenosis, known difficult airway. The exclusion criteria: tracheal intubations were canceled, or operations were canceled, or patients' data were missing. HMD ultrasound measurements of patients in a sniffing position and other usual airway evaluations were performed before general anaesthesia induction. The primary outcome was the intubation difficulty level. Predictive values were calculated.

RESULTS

We successfully enrolled 2357 patients (62 difficult intubation patients) in the cohort study for analysis. The area under the receiver operating characteristic curve (AUC) of the HMD and TMD for predicting difficult intubation was 0.86 (95% CI, 0.84-0.87) and 0.77 (95% CI, 0.75-0.78) respectively (comparison: P <  0.001). With an optimal cutoff value of HMD ≤ 4.9 cm, we observed a sensitivity and specificity of 0.90 (95% CI, 0.80-0.96) and 0.73 (95% CI, 0.71-0.75). Meanwhile, of TMD ≤ 7.0 cm, the sensitivity and specificity were 0.77 (95% CI, 0.65-0.87) and 0.65 (95% CI, 0.63-0.67) respectively.

CONCLUSION

In comparison to TMD, HMD measured by ultrasound was more sensitive in predicting difficult intubation.

EOY summary 2018

Clinical monitoring and technology are at the heart of anesthesiology, and new technological developments will help to define how anesthesiology will evolve as a profession. Anesthesia related research published in the JCMC in 2018 mainly pertained to ICU sedation with inhaled agents, anesthesia workstation technology, and monitoring of different aspects of depth of anesthesia.