Evaluation of Upper Airway Ultrasound-derived Indexes as Predictors of Difficult Airway

Upper airway ultrasound is a valuable, non-invasive, simple, and portable point of care tool for evaluation of the airway, even in the presence of anatomic distortion caused by pathology or trauma. The ultrasound technology is being increasingly adopted in modern anesthesiology practice. As early as in 1984, some authors have recommended its use to guide venous cannulation, because it shortens procedural times, reduces the number of failed puncture attempts, and minimizes complications. On the other hand, ultrasound-guided techniques are considered the gold standard for peripheral nerve blocks.

As ultrasound becomes more widespread, it is important to for anesthesiologists to be aware of the expanding applications of this technology. Current and potential future applications of ultrasound in anesthesiology are wide and include regional anesthesia, neuraxial and chronic pain procedures, vascular access, airway assessment, lung ultrasound, ultrasound neuro-monitoring, gastric ultrasound, focused transthoracic echography, trans-esophageal echocardiography and vascular Doppler flow assessment. The major disadvantage is inter-observer variability, and the fact that it requires is a unique skill that requires continuing training and experience to master the technology. In order to be successful with this technique, it is important to develop a thorough understanding of the sonoanatomy. The normal or abnormal structures need to be imaged and interpreted before any intervention.

Airway management is one of the most important tasks for anesthesiologists. Access to the airway should be safe, fast and efficient. Appropriate planning is crucial to avoid morbidity and mortality when difficulty is anticipated. Inability to maintain airway ventilation is a life-threatening situation that may warrant emergent surgical access to prevent devastating consequences. A thorough assessment of the airway is recommended to predict difficulty. Multiple clinical predictors have been used in clinical practice; however, most of them are associated with low predictive values. In consequence, a comprehensive airway examination that incorporates both quantitative and qualitative tests increases the probability of predicting difficult intubation. Regardless of the method of airway evaluation, it is important to acknowledge that clinical airway assessment is not fully accurate and can produce both false-negative and false-positive results.

There is a growing academic interest in the ability of ultrasound to determine airway size to estimate appropriate endotracheal tube size. Ultrasound enables us to identify important sonoanatomy of the upper airway including thyroid cartilage, epiglottis, cricoid cartilage, cricothyroid membrane, tracheal cartilages, and esophagus. Transverse and parasagittal views can help diagnose supraglottic, glottic and infraglottic airway conditions and aid the anesthesiologist in airway management. Ultrasonography has brought a paradigm shift in the practice of airway management. With increasing awareness, portability, accessibility and further sophistication in technology, it is likely to find a place in routine airway management.