The use of the algorithm was effective in managing the airways in this protocol. This research showed that most airways in elective surgeries scenarios can be managed with a simple algorithm limited to a small number and low-cost airway devices. It was also demonstrated that this sequence can be applied in a major teaching hospital where physicians under training perform intubations. Although guidelines and recommendations for the management of unexpected difficult airway already exist [2, 4, 10, 11], they are not wholly applicable in particular places or conditions. This algorithm was followed aiming to adopt few mandatory devices which can be easily introduced into an OR daily routine.
The McCoy blade associated with external laryngeal pressure improved the laryngoscopic view in all patients with CLm grade 2A and 2B. Our finds are compatible with previous literature. Studies have been consistent in their findings that improvement in Cormack-Lehane grade 3 views to grade 2 or better is significant occurring in 44 to 91% of cases [10, 11, 12, 13]. Literature also demonstrated that the McCoy blade is less useful in easy laryngoscopies. In practice, however, we observed that it is not a problem, since a good view of the larynx can be achieved with the levering in neutral position [10, 13]. External laryngeal pressure, used as BURP maneuver in our study seemed to be effective because it moved the glottic opening into the laryngoscopic line of vision. Thus, articulated McCoy blade and BURP maneuver had an additive effect in most of our patients.
There were no modifications in only 8 patients with CLm grade 3A. Previous studies also had similar problems when they analyzed the applicability of McCoy blade. The poor efficacy of McCoy blade was associated to patients' diseases [14] and in some cases it was not enough to lift the base of the tongue and vallecula [14, 15]. In this research, three of these patients were submitted to total thyroidectomy and five presented Mallampati grade 3 or 4. It is possible that the underlying pathology and the soft tissue oropharyngeal disproportion may contribute to decrease visualization or mobility of the epiglottis in these cases.
The bougie was used the third step because of its efficacy, simplicity of use and low cost. Reports have demonstrated a high success rate of tracheal intubation associated with the use of bougie in case of unpredicted difficult laryngoscopy [1, 3, 16]. In this study, bougie was used to aid intubation in patients with CLm grade 2B and 3A, being effective in all cases.
In comparison with other studies, it was found a similar proportion of grade 3 views (4.8%) at laryngoscopy with the blade in neutral position. The incidence of grades 3 or 4 laryngeal views varies between 0.3% and 13.3% in unselected populations [17, 18]. This led us believe that the McCoy blade in neutral position functions similarly to the Macintosh blade for glottic view.
This study has some limitations. Reports of CICO cases varies from 1 in 5000 [19] to 1 in 32000 [20]. The patient population is small and can miss the most difficult cases. During elective general anesthesia, situations such as CICO or CLm 3B and 4 are rare events. Incidence of Cormack-Lehane grade 3 and 4 is around 4.9% [21] and CLm grade 3B is close to 1.8% [17]. Because of that, a higher number of subjects is important for a more accurate analysis of our algorithm. The study did not reach the final step of the algorithm using LMA Fastrach™. Another limitation is that successful use of the algorithm was based on practical experience of only two researchers who were second- and third-year residents. Besides that, during the study they may have improved their skills with the algorithm devices. Thus, their final cases could be biased by acquired experience.