In 12 patients, a size 6.5 or 9.0 endotracheal tube was substituted for the standard size in the study, at the request of the surgeon or the attending anesthesiologist, without impact on the intubation technique. Data collection was incomplete in 5 patients: 4 patients were unable to reliably execute the upper lip bite test and, in 1 patient, the measurement of neck circumference was accidentally omitted. No patients and no data were excluded from the analysis. No adverse events or complications associated with an increase in the use of the BRF were noted during this study.
In this study, successful tracheal intubation with the BRF occurred in 396 (99%) cases. In all 4 cases where intubation with the BRF alone was not successful, failure to visualize the glottis appeared to be the result of difficulty in mobilizing the epiglottis to create an opening between it and the posterior pharyngeal wall without the BRF passing directly into the esophagus. DL performed simultaneously with BRF is a technique that has been described before10 and that allows the anesthesiologist to lift the epiglottis off the posterior pharynx. When attempted in 2 of the cases of failed BRF in this study, this technique proved successful. In the other 2 failures with BRF alone, the anesthesia team chose to intubate using DL and another intubation aide; DL + BRF was not attempted (but may also have been a successful alternative). The success rate for BRF intubation in this study is similar to the 98.3% success rate previously reported in a case series of 60 patients6 and somewhat better than the 91.7% success rate with the BRF reported by Wahlen and Gercek19 (12 patients) or the 86.1% reported by Wong20 (36 patients). The success rate for BRF in this study is comparable with the 99.75% success obtained in a similar study by this group using the GlideScope videolaryngoscope15 and with the 99.7% success rate reported for DL.21
When the study was designed, analysis of the correlation between number of intubation attempts and patient characteristics was planned.15 However, the low number of patients with >1 intubation attempt (10/400) in this study precluded this type of analysis.
In this study, decreased mouth opening, increased BMI, and higher Cormack and Lehane grade were independently associated with time to intubation with the BRF. All these 3 factors are also associated with difficult DL. However, decreasing TMD appears to be correlated with slightly shorter (Fig. 1) intubation times with the BRF, in contrast to the findings of studies evaluating DL or videolaryngoscopy.1,15 This could be attributable to key differences between DL and BRF: with DL, a longer TMD allows proper alignment of the oral, pharyngeal, and laryngeal planes as the operator displaces the anterior pharyngeal structures with the laryngoscope to visualize the glottis22; with the BRF, however, the anterior pharyngeal wall is not displaced by the BRF itself, the jaw being instead lifted by the operator to create an opening beneath the epiglottis to allow passage of the scope and glottic visualization. Although it is not possible to definitely explain from our results why decreased TMD predicted slightly shorter intubation times, it is interesting to note that the BRF was designed for pediatric patients with a receding chin,7 and it is therefore possible that the fixed angle and length of the distal portion of the scope may make it particularly suitable for intubation of patients with short TMDs.
Mouth opening was inversely correlated with time required for intubation with the BRF. A mouth opening of <35 mm has also been predictive of difficult DL in previous studies,23,24 although results of a meta-analysis were less clear.25 One previous study26 compared DL with the BRF in 76 patients with simulated difficult airways (using a rigid cervical collar to restrict cervical movement and mouth opening). In this study, successful tracheal intubation occurred in 82% of the BRF group versus only 40% in the DL group. It may be that, although a small mouth opening does prolong intubation times with the BRF, the BRF’s small size could still make it less susceptible to outright failure than DL.
Increasing BMI also predicted the time required for intubation, as is the case in studies exploring the relationship between BMI and failed tracheal intubation using DL.2,27 Redundant mucosal tissues hampering glottic visualization may explain this finding in both techniques.
Finally, Cormack and Lehane grade III at DL also correlated with longer intubation times at BRF. A Cormack and Lehane grade of III or IV is a well-established criterion for difficult DL.21 The BRF has previously been studied versus flexible fiberoptic bronchoscopy in unanticipated difficult airways, as defined by failed intubation at DL or Cormack and Lehane grade III or IV at DL. Rudolph et al.11 had a 100% success rate with BRF in the unanticipated difficult airway (n = 116), including success with BRF after 2 failed attempts at fiberoptic bronchoscopy intubation. Kim et al.10 had a 90% (18/20) success rate with BRF. In this study, Cormack and Lehane grade III at DL was observed in 6 (1.5%) patients, an incidence similar to previous studies that noted only the best glottic view obtained with or without backward upward rightward pressure28; BRF intubation without assistance with a laryngoscope was successful in 5 of these 6 patients (83%).
Figure 2 presents an algorithmic interpretation of the findings of this study. In addition to having a high success rate as a primary intubation tool, the BRF is an attractive alternative to DL in patients with short TMDs, with or without reduced mouth opening. Conversely, patients with a high BMI, or in which BRF alone fails, may benefit from a combined BRF and DL technique. Other maneuvers such as head tilt or neck extension may also be useful in modifying the spatial relationship between the epiglottis and the anterior pharyngeal wall. Further studies could evaluate the clinical utility of the addition of DL to BRF, as well as other possible maneuvers.
Our study has several limitations. The use of end-tidal CO2 as a confirmation for successful intubation led to slightly longer intubation times when the capnograph sampling line was longer (when the head of the patient was far from the anesthesia machine). Another limitation is that the Cormack and Lehane grade at DL was determined by the same person who subsequently performed BRF, which could potentially have influenced the performance of the second technique. Furthermore, because only patients receiving neuromuscular blockade were studied, patients with nonreassuring airways in whom awake intubation or intubation without paralysis was selected were not included. Anticipated difficult airways using DL may therefore be underrepresented in our patient group.
In conclusion, mouth opening, BMI, and high Cormack and Lehane grade predict a longer time to successful intubation, as has already been noted with other intubation techniques, such as DL and videolarygoscopy. Decreasing TMD predicts slightly shorter intubation times with BRF, a relation that may reflect the original patient population for which BRF was designed. The high success rate of BRF in this study, the unique relationship between TMD and intubation times, and the possibility of further increasing BRF success rates by combining it with DL help define the role of BRF in the management of difficult intubation.
Name: Michal Nowakowski, MD.
Contribution: This author helped with study design and conduct, as well as data collection and analysis and manuscript preparation.
Attestation: Michal Nowakowski attests to the integrity of the original data and the analysis reported in this manuscript and approves the final manuscript.
Name: Stephan Williams, MD, PhD.
Contribution: This author helped with study design and conduct, as well as data analysis and manuscript preparation.
Attestation: Stephan Williams attests to the integrity of the original data and the analysis reported in this manuscript and is the archival author.
Name: Jason Gallant, MD.
Contribution: This author helped with study design and conduct, as well as data collection.
Attestation: Jason Gallant approved the final manuscript.
Name: Monique Ruel, Inf CCRP.
Contribution: This author helped with study design and conduct.
Attestation: Monique Ruel approved the final manuscript.
Name: Arnaud Robitaille, MD, FRCPC.
Contribution: This author helped with study design and conduct, as well as data analysis and manuscript preparation.
Attestation: Arnaud Robitaille attests to the integrity of the original data and the analysis reported in this manuscript.
This manuscript was handled by: Sorin J. Brull, MD.
The authors would like to thank Martin Ladouceur, PhD, Principal Advisor in Biostatistics, CR-CHUM.
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© 2016 International Anesthesia Research Society
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