Conventional tracheal intubation using direct laryngoscopy is the most common intubation technique in daily clinical anaesthetic practice. The curved Macintosh blade is widely used in this context. The Cormack and Lehane (C&L) score,1,2 describing the visibility of the vocal cords or the pharynx during direct laryngoscopy, is the most commonly used tool to grade the conditions of direct laryngoscopy and ease of tracheal intubation. More recently, the ‘portion of glottic opening’ (POGO) score was introduced as a new classification estimating the proportion of the glottis, which is visible on laryngoscopy.3,4 A C&L score of 1 represents a POGO score of 50 to 100%. Usually, these patients can be intubated easily in a single attempt. In patients with a C&L Score of 2 or a POGO Score below 50%, facilitation of tracheal intubation should also be possible without the need for an alternative or advanced intubation technique. In contrast, patients presenting with a C&L Score of 3 (a POGO Score of 0%) are potentially difficult to intubate. In these patients, a malleable stylet bent like a hockey stick and protruding from the tube tip where applicable and/or the backward-upward-rightward-pressure (BURP) procedure might serve as feasible tools to facilitate successful tracheal intubation in the hands of a very experienced user. In the explicitly difficult intubation setting (C&L score 4), visualising techniques such as videolaryngoscopes or video-stylets might be more promising options.5,6
A common way to cope with a moderately difficult laryngeal view (e.g. C&L 2 or POGO below 50%) is to elevate the tip of the tracheal tube. The elevated tip of the tube facilitates its insertion through the glottic opening, which is normally covered by the epiglottis. An intubation technique that limits the number of intubation attempts as well as the duration of laryngoscopy while significantly increasing the success rate seems to be desirable. In this context, ‘reflective intubation’, a simple auxiliary technique to manually modify the shape of the tracheal tube during laryngoscopy, has been described recently.7 Important advantages of this technique are that the intubation attempt does not have to be interrupted and neither additional intubation attempts nor additional equipment are necessary.
Reflective intubation facilitates successful intubation with a specific move of the hand holding the tracheal tube (usually the right hand). Gentle pressure is applied by the middle finger of the right hand to the shaft of the tube about 2 cm above the upper dental ridge (or the upper gums in edentulous patients) using the teeth or gums as a fulcrum (Fig. 1). This manoeuvre causes an upward movement of the distal segment of the tube. Both ends of the tube approach each other, similar to a reflection in a mirror, which gives rise to the name of the procedure. On the basis of the change in the curvature of the tube, there may be an improvement in direct visualisation of the glottis/pharynx (as graded by the C&L score), thus facilitating tracheal intubation. We therefore investigated the overall success rate of the reflective intubation technique in a prospective case–control study.
Materials and methods
Ethical approval for this study (Ethical Committee No. KEK-StV-Nr. 50/13) was obtained from the Ethical Committee of the Kanton Zurich, Switzerland (Chairperson Prof. P. Meier-Abt) on 29 October 2013. One hundred patients undergoing elective surgery, which required the use of tracheal intubation, were enrolled in this study. A patient's inclusion was simply based on their availability and suitability. All patients provided written informed consent during the preoperative visit of the anaesthesiologist on the day before surgery. Exclusion criteria were age under 18 years and American Society of Anesthesiologists (ASA) physical status 3 or more. Sex, age, height, weight and Mallampati score were also documented. On the day of surgery, patients were treated in accordance with local clinical guidelines. Tracheal intubation and related measurements were performed exclusively by the two authors of this article, who are both familiar with the reflective intubation technique and are also well prepared to cope with unexpected airway difficulties of all kinds. All patients received midazolam 7.5 mg orally for premedication. General anaesthesia was induced with propofol 1.5 mg kg−1, fentanyl 3 μg kg−1 and the nondepolarising muscle relaxants rocuronium 0.6 mg kg−1 or atracurium 0.5 mg kg−1. General anaesthesia was maintained with sevoflurane or propofol infusion guided by clinical parameters. Complete neuromuscular blockade (the absence of palpable twitches in any of the fingers in response to supramaximal train-of-four stimulation of the ulnar nerve at the wrist) was confirmed before the first intubation attempt. Tracheal intubation was performed in the supine position in all patients, and followed a designated flow chart (Fig. 2).
First, direct laryngoscopy was performed, and C&L grade and POGO percentage were assessed. Tracheal intubation using a regular tracheal tube (no stylet inserted) was attempted. Successfully intubated patients formed the ‘Easy Intubation’ group (group E). The remaining patients (‘noneasy’ subgroup) underwent an additional intubation attempt using reflective intubation, without interrupting the initial laryngoscopy. Patients successfully intubated with reflective intubation formed the ‘Moderately Difficult Intubation’ group (group M). Finally, patients whose airway could not be secured with the reflective intubation technique were categorised as the ‘Difficult Intubation’ group (group D). These patients underwent tracheal intubation using an alternative technique, including the insertion of a malleable stylet, supraglottic airway, flexible fibreoptic or SensaScope video-stylet. In some cases, when using a stylet, the application of the BURP external manoeuvre on the larynx8 resulted in success. Time to intubation was noted and defined as the time between the insertion of the laryngoscope into the mouth and the verification/declaration that the tracheal tube was in the correct position.
During the whole procedure, oxygenation was continuously monitored by pulse oximetry. Any changes in peripheral oxygen saturation (SpO2) during the intubation procedure were documented. If SpO2 was below 90%, the intubation procedure was interrupted and manual ventilation was initiated. Finally, a suitable alternative technique for securing the airway was applied.
After surgery, all patients were transferred to the postanaesthesia care unit (PACU) and closely monitored by the PACU staff for at least 2 h, which represents the standard of care at our institution. Before being discharged, all patients were asked about newly developed sore throat and examined for dental damage. To our knowledge, no data are available as regards the success rate of reflective intubation. On the basis of this fact, and assuming the high feasibility of the proposed study, we decided to include 100 patients and to observe whether this sample size led to results that could be analysed statistically.
The results were analysed with SPSS statistics software (Version 21; IBM SPSS Statistics, Armonk, New York, USA). Descriptive statistics are presented as mean ± standard deviation for continuous variables, as counts for categorical variables and as percentages where appropriate. The χ2 test was used to compare categorical variables among the groups. For analysis between the groups, a one-way analysis of variance (ANOVA) or the Kruskal–Wallis test was used to compare parametric and nonparametric data respectively. A P value less than 0.05 was considered to be statistically significant. No initial power analysis was calculated before the start of the study.
One hundred patients (69 women and 31 men) were included in this prospective case–control study. The sample size was chosen to assess the success rate of reflective intubation and n = 100 was found to be sufficient. The uneven sex distribution resulted from the fact that a major part of the investigation was conducted in the gynaecological operating theatre. Overall, 48 patients had a Mallampati score of 1, 43 patients a score of 2, eight patients a score of 3 and one patient a score of 4 (Table 1). The overall POGO score of all patients was 50 ± 35%. Tracheal intubation was achieved easily in 46 patients at the first attempt (group E). Of the remaining 54 patients, tracheal intubation was successful using the reflective intubation technique in 42 patients (group M). Twelve patients required additional intubation techniques (group D) (Fig. 2).
The three groups were different in size but not significantly different by biometric values (Table 2). Further differences were found in laryngeal visibility (C&L and POGO scores), time to intubation and in the Mallampati score predicting laryngeal view. Peripheral oxygen saturation was stable in nearly all patients and never reached critical values (SpO2 mean 98 ± 2%; minimum 90%). Postoperatively, the incidence of sore throat was significantly greater in patients in group D who had undergone three or more intubation attempts (P < 0.01). No dental damage was reported in any patient.
Epidemiological data of our study population, distribution of Mallampati scores9,10 and best possible view of the glottis during laryngoscopy1,3 were comparable to those in previous reports. We therefore conclude that our results might be representative for a standard population of patients undergoing elective surgery.
Tracheal intubation was achieved easily in almost half of our patients (46%) without the need for an additional aid or technique. At first glance, this number might seem to be rather low. However, it should be emphasised that no additional aid or facilitating technique, for example BURP, was applied during the initial intubation attempt. Although BURP might be a simple manoeuvre, anaesthesiologists must be aware that it still represents an ‘invasive’ procedure and might therefore not only provoke clinical concerns but sometimes even distort the laryngeal view.11,12 The overall success rate of our initial intubation attempt (including noninvasive and reflective intubation) was close to 90%, which is comparable with previous publications. In the clinical setting, unexpected difficulties during laryngoscopy occur in 5.8% of all patients and poor glottis visualisation is estimated to be encountered in 1 to 9% of intubation attempts.10,13 We therefore conclude that the availability of reflective intubation as well as other alternative intubation methods and aids is crucial, as more than half of the patients in our study needed a modified approach after a straightforward insertion of the tracheal tube at the first attempt proved to be unsuccessful.
The fact that there were no significant alterations in oxygenation (as assessed by continuous measurement of SpO2) clearly showed that a staged and stepwise approach of alternating the intubation technique, as carried out in the study in accordance with our flow chart (Fig. 2), is suitable during daily clinical practice.
The finding that 46% of all patients revealed easy intubation conditions is gratifying. However, we should still be concerned about the remaining 54% and, in particular, the 12% of the total study population (and 22% of the ‘noneasy’ subgroup) who were rated as ‘Difficult’ (group D). The majority of the patients who were not in group E presented only a moderate difficulty level and the trachea could be intubated using the reflective intubation technique. Thus, reflective intubation seems to be an appropriate method in cases of limited glottis visibility, that is C&L 2 or 3a or POGO score less than 50% (but still higher than 0%). In C&L grade 3a the epiglottis can be lifted with the laryngoscope blade from the posterior pharyngeal wall (thus creating access to the glottis), while in 3b the epiglottis cannot be elevated at all. This is an important distinction, because any technique based on bending the tracheal tube (including reflective intubation) might be successful in C&L 3a but is very likely to fail in C&L 3b. Therefore, C&L 3b requires the (immediate) availability of different, more sophisticated equipment along with a higher degree of airway management skills by the anaesthesiologist in charge.
The results of our study confirm the fact that the use of reflective intubation as a first-line variation of the initial intubation technique should be advocated, as it is not only feasible and leads to more successful intubations within the first attempt, but it also avoids the need for additional instruments to be involved, and can be applied instantly and easily during the initial intubation attempt. It is solely based on an additional movement exerted by the intubator, without the necessity to interrupt the ongoing laryngoscopy. Not only does reflective intubation reduce the time to intubation (by avoiding the need for additional equipment that has to be procured and prepared for use), but it also applies less strain and tension on to the temporomandibular joints and teeth than if multiple laryngoscopy attempts are conducted until the airway is finally secured.14,15 In our study, reflective intubation was able to overcome encountered difficult laryngoscopy in 78% of patients who were not in group E. Thus, reflective intubation seems to be an excellent, feasible and simple technique as a first-line measure in unexpected difficult laryngoscopies/intubations. It should be noted that because the study was small, there is no data to indicate the usefulness of reflective intubation in patients with a C&L of 3b or higher.
This study was sized by prioritising the evaluation of success rate of reflective intubation, and therefore it was underpowered for conclusions regarding any side effects such as sore throat. However, the incidence of sore throat was high enough to attain a significant level in patients undergoing three or more intubation attempts (group D). Further studies with stringent power analyses are indicated to investigate additional clinical aspects comprehensively.
A limitation of this investigation is the fact that all intubations were performed by two experienced anaesthetists. This had the benefit of having constant conditions, but the results cannot represent the skill level of a mixed-user population comprising a portion of novices.16,17 Therefore, further investigations of reflective intubation with a larger number of patients and a more diverse user population are recommended in order to understand better the full potential of reflective intubation.
The reflective intubation technique seems to be an appropriate, noninvasive and promising method for intubating patients with moderately increased C&L grades and/or a decreased POGO score, and might therefore be considered for integration into daily clinical practice and teaching of airway management.
Acknowledgements relating to this article
Assistance with the study: the authors thank Dr Tobias Piegeler, MD, for proof reading and linguistic advice.
Financial support and sponsorship: none.
Conflicts of interest: none.
Presentation: results from this study were presented in a poster session during the 2nd European Airway Congress, 5 to 7 December 2013 in Istanbul (Turkey).
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