Role of Airwayultrasound in Predicting Difficult Endotracheal Intubation in Patients Undergoing General Anesthesia

Unpredictable difficult endotracheal intubation remains a challenge especially if difficult ventilation occurs. Difficult intubation is associated with many severe fatal complications including air way trauma, laryngospasm, hypoxemia, arrhythmias and potential cardiac arrest. Therefore, preoperative evaluation and prediction of potential difficult airway is very important.

Several screening tests are used in clinical practice to identify patients at the risk of difficult airway. Despite their accuracy and benefit, a small number of patients classified to an easy airway may still present an unexpected difficulty. Predicting a difficult airway is not at all an easy task for all patients .

Incidence of difficult airway and difficult intubation varies from 5% to 22% with important implications for clinical practice and patients' outcomes .

There are multiple scores used for airway assesment ,the commonest one is LEMON score. LEMON is an airway assessment score that measures factors associated with difficult intubation such as obesity, head and neck movement, jaw movement , receding mandible, long upper incisors, Mallampatti scores, maxillary incisor characteristics, decreased mouth opening ,shorten thyromental distance and short neck .

Diagnostic criteria for LEMON scoring system :

L- Look. E- Evaluation using the 3-3-2 rule. M- Mallampati. O- Obstruction. N- Neck mobility. Ultrasound (US) imaging technique is simple, portable, noninvasive tool helpful for airway assessment and management. In the last few years, there have been some reports that described various roles of US imaging in airway management. It helps in rapid assessment of the airway anatomy, not only in operation theatre but also in the intensive care unit and emergency department.

Various clinical applications of US imaging of the upper airway include identification of endotracheal tube (ETT) placement, guidance of percutaneous tracheostomy and cricothyroidotomy, detection of subglottic stenosis, prediction of difficult intubation and post-extubation stridor, prediction of paediatric ETT and double-lumen tube (DLT) size.

Recently there are researches about airway assesment by ultrasound. Several airway assesment indicies are used to help in prediction of difficult endotracheal intubation. The most commonly used indices are distance from skin to epiglottis, distance from skin to vocal cord level, and distance from skin to hyoid bone.