title: Pilot study to determine the utility of point-of-care ultrasound in the assessment of difficult laryngoscopy.
abstract: OBJECTIVE
  Prediction of difficult laryngoscopy in emergency care settings is challenging. The preintubation clinical screening tests may not be applied in a large number of emergency intubations due to the patient's clinical condition. The objectives of this study were 1) to determine the utility of sonographic measurements of thickness of the tongue, anterior neck soft tissue at the level of the hyoid bone, and thyrohyoid membrane in distinguishing difficult and easy laryngoscopies and 2) to examine the association between sonographic measurements (thickness of tongue and anterior neck soft tissue) and difficult airway clinical screening tests (modified Mallampati score, thyromental distance, and interincisor gap).
  
  
  METHODS
  This was a prospective observational study at an academic medical center. Adult patients undergoing endotracheal intubation for an elective surgical procedure were included. The investigators involved in data collection were blinded to each other's assessments. Demographic variables were collected preoperatively. The clinical screening tests to predict a difficult airway were performed. The ultrasound (US) measurements of tongue and anterior neck soft tissue were obtained. The laryngoscopic view was graded using Cormack and Lehane classification by anesthesia providers on the day of surgery. To allow for comparisons between difficult airway and easy airway groups, a two-sided Student's t-test and Fisher's exact test were employed as appropriate. Spearman's rank correlation coefficients were used to examine the association between screening tests and sonographic measurements.
  
  
  RESULTS
  The mean (±standard deviation [SD]) age of 51 eligible patients (32 female, 19 male) was 53.1 (±13.2) years. Six of the 51 patients (12%, 95% confidence interval [CI] = 3% to 20%) were classified as having difficult laryngoscopy by anesthesia providers. The distribution of laryngoscopy grades for all subjects was 63, 25, 4, and 8% for grades 1, 2, 3, and 4, respectively. In this study, 83% of subjects with difficult airways were males. No other significant differences were noted in the demographic variables and difficult airway clinical screening tests between the two groups. The sonographic measurements of anterior neck soft tissue were greater in the difficult laryngoscopy group compared to the easy laryngoscopy group at the level of the hyoid bone (1.69, 95% CI = 1.19 to 2.19 vs. 1.37, 95% CI = 1.27 to 1.46) and thyrohyoid membrane (3.47, 95% CI = 2.88 to 4.07 vs. 2.37, 95% CI = 2.29 to 2.44). No significant correlation was found between sonographic measurements and clinical screening tests.
  
  
  CONCLUSIONS
  This pilot study demonstrated that sonographic measurements of anterior neck soft tissue thickness at the level of hyoid bone and thyrohyoid membrane can be used to distinguish difficult and easy laryngoscopies. Clinical screening tests did not correlate with US measurements, and US was able to detect difficult laryngoscopy, indicating the limitations of the conventional screening tests for predicting difficult laryngoscopy.
authors.affiliation: Department of Emergency Medicine, University of Arizona Health Sciences Center, Tucson, USA. sriadhikari@aol.com
authors.forename: Srikar
authors.initials: S
authors.lastname: Adhikari
authors.forename: Wes
authors.initials: W
authors.lastname: Zeger
authors.forename: Charles
authors.initials: C
authors.lastname: Schmier
authors.forename: Todd
authors.initials: T
authors.lastname: Crum
authors.forename: Andy
authors.initials: A
authors.lastname: Craven
authors.forename: Ilir
authors.initials: I
authors.lastname: Frrokaj
authors.forename: Huiling
authors.initials: H
authors.lastname: Pang
authors.forename: Valerie
authors.initials: V
authors.lastname: Shostrom
mesh_terms: D000328:Adult; D000368:Aged; D002983:Clinical Competence; D005260:Female; D006801:Humans; D006928:Hyoid Bone / Q000000981:diagnostic imaging; D007828:Laryngoscopy / Q000379:methods; D008297:Male; D008875:Middle Aged; D009333:Neck / Q000000981:diagnostic imaging*; D010865:Pilot Projects; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D011446:Prospective Studies; D018709:Statistics, Nonparametric; D014059:Tongue / Q000000981:diagnostic imaging*; D014463:Ultrasonography