Is older still good, or even better? Evaluation of possibility of using Miller laryngoscope for intubation in adults and comparison with the most widely used Macintosh laryngoscope. Protocol of a crossover randomized control trial

BACKGROUND: Macintosh laryngoscope is the most widely used laryngoscope for intubation. In some patients, e.g. with flaccid, drooping, aplastic epiglottis, usage of this laryngoscope, or even videolaryngoscopes, may not provide visualization of a glottis. Elevation of the laryngopharynx, like in intubation with Miller laryngoscope, may significantly improve intubating conditions. METHODS: An anaesthesiologist with over 20 years of experience will perform direct laryngoscopy with randomly chosen Miller or Macintosh blade, evaluating the visibility of rima glottidis with Cormack-Lehane classification and POGO score with and without external laryngeal pressure. Then the second evaluation of glottis with other blade type will be obtained and the patient will be intubated. Comparison of the rima glottidis visibility when using both blades will be the primary endpoint of the study. The secondary endpoints consist of: demonstrating whether there is a group of adult patients in whom the use of the Miller blade associated with better vocal cord visibility may be predicted based on an anesthesiological examination, and whether external laryngeal pressure improves vocal cord visualization more when using the Miller blade compared with the Macintosh blade. SAMPLE SIZE: We performed minimal sample size calculations based on the data derived from the first 60 patients. We assessed the minimal sample size to obtain the alpha of 5 % and power of 90 %. We decide to enroll at least 286 patients. DISCUSSION: this will be the first trial assessing Miller and Macintosh blades in the same population of adult patients. It will determine group of patients in whom Miller laryngoscope will provide better visualization of rima glottidis than Macintosh blade and associated technique, diminishing rate of prolonging intubations and reducing possible aftermaths of hypoxia.