To evaluate the role of pre-operative ultrasound assessment of airway in predicting difficult mask ventilation.

Effective mask ventilation plays a critical role in safe management of airway before intubation or after failed intubation. Failure to provide adequate oxygenation resulting from difficult mask ventilation (DMV) can lead to life threatening complications in both elective and emergency settings. Thus, it is very important to identify patients at risk of DMV. Prediction of DMV based on clinical evaluation of anesthesiologist alone is not always accurate and may lead to unanticipated DMV. This necessitates the need for diagnostic tools which may be considered adjunct to the conventional pre-operative assessment in predicting DMV and can contribute to safer airway management.

During the last few years ultrasound has been used widely in the operating room for ultrasound guided procedures such as nerve block or central venous access. It has been suggested that pre-operative ultrasound measurement of airway when combined with commonly used screening tests and risk factor assessment for DMV might improve the ability to predict the difficulties.

Previous studies have found the anterior neck measurements using ultrasound to be associated with DMV, especially the distance from skin to hyoid bone (DSHB). Ultrasound measurement of tongue thickness to oral cavity height ratio (TT/OCH) has been observed to be consistent with CT findings of tongue volume to oropharyngeal volume ratio and tongue thickness to oral cavity height ratio.

Under general anesthesia, the tongue may obstruct the upper airway by pushing the soft palate against the posterior pharyngeal wall, obstructing both the nasal and oral cavities or the tongue may close the oral cavity when the nose is obstructed, then acting as a one-way valve obstructing expiration. Thickness of tongue relative to oral cavity height may predispose to upper airway obstruction and result in DMV. Thus, we thought it would be worthwhile to study the role of ultrasound measurement of tongue thickness to oral cavity height (TT/OCH) ratio in predicting DMV. So, we aim to evaluate the role of ultrasound guided TT/OCH ratio and anterior neck measurements in predicting DMV.