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.