Can point-of-care ultrasound predict the difficulty in intubation? - A prospective observational study

Airway ultrasonography (USG) parameters have been used to predict difficult tracheal intubation. However, the available literature on this topic is still controversial. This study aims to assess the role of preoperative airway USG parameters, namely hyomental distance in the head neutral (HMDn), head extended position (HMDe) and their ratio (HMDR), pre-epiglottic space (PreE), and the distance from the epiglottis to the vocal cords midpoint (E-VC) and their ratio (PreE/E-VC), in predicting difficult intubation.

This prospective observational study was conducted on 190 patients. Preoperative USG airway parameters were measured. The primary outcome was to correlate these USG parameters with the Cormack-Lehane (CL) grade. The secondary outcome was to correlate these USG parameters with the intubation difficulty score (IDS). Kendall's tau correlation test and receiver operating characteristic curve analysis were performed.

A positive correlation was observed between PreE/E-VC ratio and CL grade [Kendall's tau: 0.423 (95% confidence interval (CI): 0.326, 0.513; P < 0.0001], while HDMR showed a non-significant correlation with CL grade [Kendall's tau: -0.0614 (95%CI: -0.183, 0.0569); P = 0.211]. PreE/E-VC ratio also showed a positive correlation with IDS [Kendall's tau: 0.391 (95%CI: 0.305, 0.471); P = <0.0001), while HDMR did not show any correlation with IDS [Kendall's tau: -0.0405 (95%CI: -0.174, 0.084); P = 0.409]. PreE/E-VC ratio >1.61 cm had 77.8% sensitivity and specificity of 86% to predict CL grade >2, while ratio >1.18 cm had a sensitivity of 71.7% and specificity of 76.4% to predict IDS ≥1.

The USG measurement of the PreE/E-VC ratio correlated with CL grade and IDS, while HMDR poorly correlated with CL grade and IDS and thus failed to predict difficult intubation.