Predicting difficult laryngoscopy for tracheal intubation: an approach to airway assessment.
Tracheal intubation by direct laryngoscopy is an essential skill for physicians working in the operating room, emergency room or intensive care unit settings. While tracheal intubation can usually be accomplished with ease by direct laryngoscopy, it is sometimes difficult or impossible because of coexisting disease or abnormal physical features. When recognized before attempts at tracheal intubation, virtually all difficult airways can be secured by the selected use of specialized tracheal intubation techniques, although many of these methods require special training, experience, assistance and equipment. When a difficult airway is unrecognized before attempts at intubation the results can be catastrophic because the personnel and equipment necessary for utilizing the specialized tracheal intubation techniques may not be immediately available and the patient's spontaneous respiratory efforts may have been eliminated by anesthetics or muscle relaxants. Thus, identifying patients who are likely to harbor an airway that cannot reliably be secured by simple direct laryngoscopy is an important skill for all acute or critical care physicians. There is an extensive research data base describing historical information, physical examination findings and radiographic features that are associated with the difficult airway. Reviewed collectively, one of the most important underlying concepts suggested by this body of research literature is that the difficult airway is a product of many anatomic and pathologic variables. A surprisingly wide variety of historical, physical examination and radiographic features associated with difficult direct laryngoscopy have been described. A rational approach to airway assessment, therefore, naturally includes a detailed history, a careful physical examination and inspection of relevant x-rays whenever time permits. As outlined in Table 5, there are specific questions to address that may warn the physician about possible airway difficulty. A number of airway assessment schemes based on physical examination findings have been proposed and tested. These schemes vary in their complexity and their clinical convenience. The simpler schemes fail to address the multifactorial nature of the problem, while the more complex systems are clinically impractical. Schemes combining the distance of the thyromental space and the visibility of the oropharyngeal structures, such as that proposed by Frerk, are perhaps the most practical and reliable of the methods proposed to date. Clearly, no one scheme is ideal. At present, preintubation airway evaluation remains a poorly quantified gestalt estimate of the chances for difficulty based on a complex juxtaposition of historical information and physical findings.(ABSTRACT TRUNCATED AT 400 WORDS)