Defining a standard intubating position using "angle finder".

Study of patients who exhibit only limited morphological abnormality yet present difficulty with direct laryngoscopy is facilitated by a standard intubating position. The "Angle Finder" instrument allows implementation of a simple reproducible geometric standard which is applied easily in formal research work and in clinical practice and teaching. The proposed standard relates to the curved (Macintosh) laryngoscope blade and a supine patient. The lower neck flexion is 35 degrees and extension of the plane of the face 15 degrees, each angle measured relative to horizontal. Initially, the standard was derived from a review of the literature, then validated in a study of the intubating practices of 10 senior anaesthetists. A more detailed study of 10 normal volunteers confirmed reproducibility and, for nine patients with a history of difficult direct laryngoscopy, the standard was shown to be appropriate.