Does laryngoscopic view after intubation predict laryngoscopic view before intubation?

STUDY OBJECTIVE: To determine if an endotracheal (ET) tube will distort the laryngeal view obtained with direct laryngoscopy measuring with the modified Cormack-Lehane scale (MCL).

DESIGN: Observational single-arm study.

SETTING: The University of Calgary teaching hospitals.

PATIENTS: Patients between 18 and 86 years of age undergoing elective surgical procedures. A total of 173 patients were enrolled and analyzed.

INTERVENTIONS: Direct laryngoscopy view obtained before ET intubation and directly after intubation.

MEASUREMENTS AND RESULTS: The MCL scales were described for each view obtained and compared to each other with each patient serving as their own control. The primary objective was a change in the best obtainable view by direct laryngoscopy from an acceptable view (MCLS 1 or 2a) to an unacceptable view (MCLS 2b, 3, or 4) or changing from an unacceptable view (MCLS 2b, 3, or 4) to an acceptable view (MCLS 1 or 2a). The main finding of this study was that the ET tube altered the MCL in 58 (33%) of 173 patients, "worsening" the grade in 30 patients (17.34%) and "improving" the grade in 28 patients (16.18%).

CONCLUSIONS: We performed a prospective observational study to address the predictive value of postintubation laryngoscopy grade in adults. The presence of the ET tube both increased visualization of the glottis and worsened the view in different subjects. The important outcome was that the presence of the ET tube did in fact change the view obtained of the larynx during direct laryngoscopy. In conclusion, postintubation MCL grades may not be reliable to predict laryngeal grade and should be used with caution in the right clinical context.