Awake fibreoptic intubation (FOI) is described as the gold standard in preventing secondary cervical injury following conventional laryngoscopy1,2 in patients with instability of the neck.1,3–6 Intubating patients while they are awake is generally preferable because there is no need for cervical hyperextension and the stabilising effect of cervical muscle tone and protective reflexes are preserved. A review of the literature on awake FOI reveals a variety of techniques all providing reasonable levels of safety and comfort.7–10 High-grade topical anaesthesia applied according to the sensory innervation of the nasal/oral cavity and tracheal mucosa should prevent spontaneous movements as well as uncomfortable coughing and gagging.11 For sufficient neurological evaluation during and after FOI, patients should ideally be awake and feel comfortable throughout the procedure. The duration of the awake FOI procedure should be kept as short as possible to minimise discomfort. Compared with the spray-as-you-go technique with a syringe, the translaryngeal injection (TLI) application of local anaesthetic agents seems to be faster and more effective in providing the required quality of topical anaesthesia for awake bronchoscopy12 or FOI.13 The Enk Fibreoptic Atomizer was developed to facilitate a wider spread of local anaesthetic than that obtained following administration via syringe and consequently may provide a similar or better quality of anaesthesia for awake FOI. To our knowledge, there has been no comparison between the use of the Enk Fibreoptic Atomizer and the TLI technique for awake FOI. Thus, our study compares these techniques in a cohort of patients at risk of secondary cervical injury with the following objectives:
- The primary outcome was the timing sequence of awake FOI following the application of topical anaesthesia using either the Enk Fibreoptic Atomizer or the TLI technique.
- The secondary outcomes were the differences in coughing or gagging during awake FOI, cardiopulmonary stability, mucosal bleeding and postoperative outcomes, such as pain, hoarseness, difficulty of swallowing and the satisfaction of patients and investigators.
Material and methods
Ethical approval for the study was provided by the Research Ethical Committee of the State Chamber of Medicine in Saxony (Sächsische Landesärztekammer – Körperschaft des öffentlichen Rechts, Schützenhöhe 16, 01099 Dresden, Germany; Registration No. EK-BR 34/08-1, 10 October 2008). The trial was performed at the Klinikum St. Georg gGmbH in Leipzig, Germany, between 2009 and 2011. Written informed consent was obtained from each patient.
All patients were scheduled for elective cervical spine decompression/stabilisation. The patients were randomly assigned into two groups using the repeated fair-coin tossing method (groupTLI and groupENK-ATOMIZER).
Because our study is the first to compare the two techniques, the sample size calculation was based on data from our previous pilot study in a similar population. However, we hypothesised that the achievable effect with the Enk Fibreoptic Atomizer compared with the TLI technique would be of a similar order with regard to the timing sequence of awake FOI. Our trial therefore aimed to detect an effect size between the two interventions in the magnitude of 200 arbitrary units assuming a conservative standard deviation of 150 arbitrary units for the samples. A smaller effect size is not clinically relevant. A total of 120 patients (60 per group) were required to achieve a power of 95% at a significance level of 5%.
We included all patients who fulfilled any one of the following criteria for awake FOI at our institution:
- ‘Cervical instability’ following cervical bone fractures, ligament instability or clinically relevant myelopathy of the cervical spine;
- Known difficult airway by definition;14
- Predicted difficult airway (patients with Mallampati classification 4, thyromental distance less than 6 cm, mouth opening less than 3 cm or known oropharyngeal/laryngeal anatomical disorders);
- A BMI greater than 40 kg m−2.
The exclusion criteria were defined as follows:
- Patients who declined the awake fibreoptic procedures;
- Contraindications to the administration of glycopyrrolate (e.g. low cardiac output syndrome or clinically relevant tachycardia), midazolam or local anaesthetic agent;
- Emergency indications for awake FOI;
- Mental disability or forms of delirium;
- Polytrauma patients and/or oro/nasal/pharyngeal bleeding;
- Contraindication to the performance of translaryngeal injection (thyroid swelling, local infection, or laryngeal disorder).
All patients were premedicated with 3.5 to 7 mg of oral midazolam 1 h prior to the surgery. Standard monitoring included an ECG, oxygen saturation (SpO2) and noninvasive blood pressure (NIBP); intravenous access was secured.
Fifteen minutes prior to applying the topical anaesthesia to the upper airway, all patients received 0.2 mg of glycopyrrolate. Further doses of midazolam were administered intravenously for anxiolysis if required throughout the procedures.
Topical anaesthesia of the oral cavity was applied using five sprays of 10% lidocaine spray (10 mg per spray). Next, the pharyngeal mucosa was anaesthetised in both groups by the stepwise application of 4% lidocaine via a Storz nebuliser (Reference #10454, Karl Storz GmbH & Co. KG, 78532 Tuttlingen, Germany). Then finally, topical anaesthesia of the supraglottic, glottic and tracheal structures was administered using either the translaryngeal injection technique in groupTLI (Fig. 1a) or the Enk Fibreoptic Atomizer (COOK Medical Europe LTD., Limerick, Ireland) in groupENK-ATOMIZER (Fig. 1b). To ensure sufficient airflow through the Enk Fibreoptic Atomizer, the device was connected to a separate oxygen source delivering 4 l min−1.
The translaryngeal injection (penetrating the cricothyroid membrane) was performed using a 23-G needle (2.5 cm length). After verification of intratracheal placement by air aspiration, 4 ml of 4% lidocaine was injected. The local anaesthetic was assumed to be nebulised and carried from the tracheal injection site to the supraglottic mucosa by the patient's coughing. After the TLI, a 1-min mandatory wait until the beginning of the endoscopy was part of the protocol. The time was recorded from the beginning of the TLI to the successful fibreoptic insertion of the endotracheal tube.
For groupENK-ATOMIZER, the local anaesthetic was administered through the working channel of the fibrescope using the Enk Fibreoptic Atomizer in two steps: nebulising 2 ml of 4% lidocaine on the vocal cords (first endoscopy) and after a mandatory 1-min wait applying 2 ml of the same agent beneath the glottis (second endoscopy). After a further 1-min mandatory wait, the endoscopy for the final intubation proceeded. The endoscope was removed immediately after each application of local anaesthetic. The time was recorded from the first insertion of the fibrescope to the successful insertion of the endotracheal tube and included the mandatory waiting periods. For fibreoptic intubation the oral approach was used in all patients.
General anaesthesia was induced using propofol (2 to 3 mg kg−1) and fentanyl (1 to 5 μg kg−1) either immediately after successful intubation or, if possible, after the fixation of the endotracheal tube. The anaesthesia was maintained by administering isoflurane.
Target outcome and scores
We first analysed the primary outcome of differences in the timing sequence of awake FOI. To this end, we evaluated the time from the final step of applying topical anaesthesia (groupTLI, translaryngeal injection: groupENK-ATOMIZER, first endoscopy for administering local anaesthetic through the working channel) to the fibreoptic insertion of the endotracheal tube. As we were interested in the total time for performing each method, we included the standardised waiting times (groupTLI 1 min after the TLI; groupENK-ATOMIZER 1 min after each of the two endoscopic applications of local anaesthetic).
To evaluate the quality of awake FOI as a secondary outcome, the levels of coughing and gagging during intubation and during the fixation of the ET were recorded on a scale of 1 to 4 [1, none; 2 to < 3 times (slight coughing and gagging comparable to ‘clearing ones’ throat’); 3=> 2 times (mild coughing or gagging lasting less than a minute); 4, persistent coughing or gagging]. Coughing and gagging were recorded separately by an independent party not involved with (but not blinded to) the intubation. In addition, a subjective evaluation by the investigators regarding the quality of the entire procedure was registered (1 = excellent, patient comfortable; 2 = good; patient still comfortable; 3 = moderate, patient occasionally uncomfortable; 4 = poor, patient uncomfortable); we also categorised the bleeding of the tracheal mucosa on a scale from 1, none; 2, discrete point of blood; 3, short trail of blood; 4, trail of blood down to the carina or further. In addition, the level of sedation was determined after tracheal intubation but before anaesthesia induction using a score modified by the authors from the Ramsay score.
Other secondary outcomes were cardiopulmonary stability and postoperative outcomes. Cardiopulmonary stability was assessed by comparing HR, NIBP and SpO2 recorded four times throughout the procedures: initially after the patient entered the operating room, before applying the topical anaesthesia in the oral cavity, before the first endoscopy and immediately after the insertion of the endotracheal tube before attempting fixation. To investigate postoperative outcomes, the patients were interviewed on the first postoperative day and asked to evaluate the experience of the awake intubation as positive, neutral, negative or having no recall. The patients were also asked to rank postoperative pain in the throat using a visual scale of 1 to 5 (1, none; 5, unacceptable pain), hoarseness (1, none; 5, aphonia) and difficulty of swallowing (1, none; 5, impossible to swallow).
For the power calculation (nQuery Advisor 6.0), the two-group t-test was used due to the approximately normal distribution of the differences.
The results were presented as mean values including standard deviation (SD) and confidence intervals (CIs) or as the median including the interquartile range (IQR) and the total range.
The Wilcoxon–Mann–Whitney test was used to analyse differences between the two groups regarding sex, BMI, doses of midazolam and local anaesthetic as well as the timing sequence of the procedures.
A Chi-square test was used to examine differences in categorical parameters such as ASA rating, Mallampati classification, history of smoking or enhanced gag reflex, endotracheal tube size and the performing investigator. In addition, a Chi-square test was used to investigate the effects of the protocol on the following categorical data: salivation, level of sedation, rate of success, coughing/gagging during the endoscopic endotracheal tube insertion and during the fixation of the endotracheal tube, ease of endotracheal tube insertion, mucosal bleeding and investigator's judgement.
Spearman's correlation coefficient was calculated to identify correlations between particular outcomes.
We recruited 120 patients (mean age, 53.7 years; range, 34 to 74 years; 63 women and 57 men) who were at risk of secondary cervical injury (Fig. 2).
With regard to the patients’ baseline characteristics, both groups were comparable with the exception of sex and endotracheal tube size (Table 1). In groupTLI, there were significantly more female patients and more of the smaller endotracheal tubes were used. There was a significant correlation between sex and endotracheal tube size. Table 1 also summarises no significant difference in the number of administered doses of midazolam or local anaesthetic between the two groups.
In one patient in groupTLI, the attempted translaryngeal injection was abandoned because air could not be aspirated through the injection needle. This patient then had topical anaesthesia using the spray-as-you-go technique, and awake FOI was performed. However, this patient's data on the awake FOI procedure and postoperative evaluation were not analysed. In three patients in groupENK-ATOMIZER, the FOI failed: all of these patients then had general anaesthesia induced and then, with inline stabilisation of the neck, FOI was performed using a laryngeal mask airway and an Aintree intubation catheter. The data of these three patients for FOI and the postoperative evaluation were not analysed.
Differences in the timing sequence
The overall time of awake FOI was measured as the primary outcome. This period included the time required for administering the topical anaesthetic using either TLI or Enk Atomizer. Awake FOI was significantly faster using the TLI technique (mean, 191 s; range, 123 to 447 s; SD, 83.5) than the Enk Fibreoptic Atomizer (mean, 430 s; range, 275 to 773 s; SD, 124.9; P = 0.0001).
Differences in the quality of awake fibreoptic intubation, cardiopulmonary stability and postoperative outcomes
Table 2 summarises the differences between groups regarding quality during awake FOI as well as the level of sedation throughout the procedure. Figure 3 illustrates the percentage of gagging during awake intubation. The patients in groupTLI experienced significantly less gagging than those in groupENK-ATOMIZER. Similarly, coughing tended to occur less frequently when using the TLI technique.
No significant differences were found regarding the rate of success, coughing/gagging during tube fixation, investigator's judgement or the level of sedation.
Table 3 illustrates the stability of the cardiopulmonary indices from the time point of beginning the topical anaesthesia to immediately after insertion of the endotracheal tube. No significant differences were reported between the groups for any of the investigated indices.
As expected, there was significantly more mucosal bleeding in groupTLI (P < 0.001). In one patient in groupTLI, very slight haemoptysis occurred on the first postoperative day, and slight bloody mucoid expectoration was noted until the third day after surgery. The patient had received anticoagulant therapy with acetylsalicylic acid: the TLI had been successful at the second attempt.
With regard to the postoperative outcomes 24 h after surgery, Table 4 summarises that there were no significant differences between the two techniques in postoperative outcomes: pain, hoarseness, difficulty of swallowing or patient memories.
The goal of this study was to compare two techniques of topical anaesthesia that both enable a comfortable and well tolerated awake FOI in patients at risk of secondary cervical injury. This study is the first to compare topical anaesthesia of the laryngeal and tracheal mucosa using the Enk Fibreoptic Atomizer with a translaryngeal injection technique of topical anaesthesia.
In the literature on awake bronchoscopy or FOI, views are divergent. Some have described TLI as being a more effective method of applying topical anaesthesia than the spray-as-you-go technique,12,15 but others found the spray-as-you-go technique to be superior to the TLI technique.16 The Enk Fibreoptic Atomizer (similar to a nebuliser described by Williams et al.17) was developed to provide a more widespread topical anaesthesia of laryngeal and tracheal structures and Piepho et al.18 showed that it did provide a better quality of anaesthesia than when conventional syringes were used to administer the local anaesthetic via the working channel of the fibrescope.
Timing sequence of the awake fibreoptic intubation
We chose the time required for awake FOI as the primary outcome of the study because it appears to be one of the clearest criteria with which to evaluate the efficiency of awake FOI. Along with sufficient topical anaesthesia, we believe that a rapid fibreoptic procedure with effective securing of the airway is crucial for ensuring patient safety and comfort. We focused only on the time related to the specific technique chosen and did not include the initial topical anaesthesia for the oral cavity and the hypopharynx. We believe that this comparison gives the most clinically relevant information, as it reflects the period of time specific to the chosen technique.
Awake FOI with the TLI technique was significantly faster than that with the Enk Fibreoptic Atomizer. The difference between the mean times (3 min and 11 s vs. 7 min and 10 s, respectively) may be clinically relevant. When the time for the initial topical anaesthesia for the oral cavity and the hypopharynx is added, this will prolong the overall duration of the procedure and may challenge a patient's patience and comfort level.
One limitation of the time comparison between the two techniques was the protocol for performing the FOI in groupENK-ATOMIZER. We administered local anaesthetic via the atomiser in separate steps (first to the laryngeal structures and second to the proximal trachea) and waited a 1-min period after each application. Because the final endoscopic intubation after these procedures was defined as the third step, we had to position the fibrescope a total of three times. However, Piepho et al.18 showed that when using the Enk Fibreoptic Atomizer, it is not necessary to remove the endoscope. As there was no other guidance in the literature, we chose a waiting period that seemed long enough for the local anaesthetic to have an effect on the mucosal tissue.
Criteria of qualitative comparison
The most important secondary outcomes were coughing and gagging during the endoscopic insertion of the endotracheal tube. Similar scoring systems to that which we used evaluating coughing and gagging are described in the literature,12,15,19 but results differ among the publications. Our investigation showed the TLI technique to be superior. Even though the local anaesthetic was administered subglottically, TLI provided a better topical block with a significant reduction in the occurrence of gagging. Although coughing tended to occur less frequently in the TLI group, it did not achieve statistical significance. Thus, with TLI, ‘controlled’ coughing seems a very effective way to spread the local anaesthetic to block supraglottic mucosal structures even though the injection site is below the glottis.
We also studied the occurrence of coughing and gagging together during the awake fixation of the endotracheal tube (Table 2). This evaluation was conducted to demonstrate that the procedure was well tolerated by the majority of the patients regardless of which regional blocking technique was performed. Tolerance of the endotracheal tube after successful intubation is an important criterion in patients with cervical instability especially for successful awake self-positioning of the head.19–22
Because we knew from our experience and from the literature8,9 that effective regional anaesthesia of the upper airway and the proximal trachea allows for a comfortable and well tolerated awake FOI without sedation, we only administered low doses of midazolam for anxiolysis. However, we could not exclude an additional sedative effect from the midazolam augmenting the local anaesthetic effect in both groups. Because there was no significant difference between the groups and 113 patients (95%) were recorded as being awake (modified Ramsay score of 1 or 2) throughout the FOI, we believe that the midazolam did not influence the results of this study in a clinically relevant manner. Most publications describe the additional administration of opioids or dexmedetomidine for sedation. From our experience, sedation may not be necessary in the presence of an effective local anaesthetic block and a structured operating room setting. Dexmedetomidine, as suggested in recent studies,23–26 may be an alternative sedative without the risk of hypoventilation. Unfortunately, at the time of our study, this drug was not available in Europe.
With regard to the invasiveness of both techniques, we found significantly more mucosal bleeding in the trachea after TLI. Because one patient receiving acetylsalicylic acid required two attempts at TLI and exhibited persistent tracheal bleeding for 3 days, we suggest carefully checking the indications for the use of the TLI technique in patients receiving anticoagulants. Tracheal or laryngeal mucosal bleeding following TLI is said to occur in 30 to 76% of patients.12,16 We could find no other published information regarding postprocedural complications associated with TLI. In one of the earliest reports on TLI for diagnostic bronchoscopy, Stone and Dominy27 found no serious complications after 446 procedures in 201 patients. Similarly, we also found no further complications.
Unfortunately, we cannot exclude an effect on the results related to the size of the endotracheal tube: significantly more patients were intubated with smaller tubes in the TLI group. The use of smaller tubes significantly correlated with the female sex and there was a significantly greater number of female patients in the TLI group.
Regarding the total doses of lidocaine used for topical anaesthesia, we administered a mean dose of 4.96 mg kg−1, well below the upper limit (approximately 7 to 9 mg kg−1) recommended.28 However, the topical administration of higher doses has been reported in the literature.29,30
Regarding cardiopulmonary stability as a measure of the stress response during awake FOI, we did not find any significant differences between the two groups. This finding is consistent with studies reporting that awake FOI performed by experienced investigators had no influence on blood pressure or heart rate.18,29 However, it is difficult to compare our results with the results from these other studies because we did not use opioids or dexmedetomidine for sedation in combination with the topical anaesthesia. It is also impossible to compare the cardiopulmonary response between awake FOI and FOI under general anaesthesia.31,32
Regarding postoperative discomfort, the majority of the patients reported no pain in the throat, hoarseness or difficulty in swallowing on the first postoperative day, with no significant differences between either group despite the differences in tube size. We conclude that both techniques, if performed by experienced anaesthesiologists, provide a high level of comfort to patients postoperatively.
Regarding the patient's experience, we found that 54% of the patients did not remember the awake procedures at all as a result of midazolam-induced amnesia. The results from the remaining patients are informative but may not be representative. Webb et al.12 performed a similar interview after an awake bronchoscopy, but they evaluated the patients’ discomfort immediately after the procedure.
In conclusion, performing an awake FOI using the TLI technique was faster and provided better anaesthesia when assessed with regard to the avoidance of gagging during endoscopic intubation. However, the TLI technique was shown to be more invasive because it involved significantly more tracheal mucosal bleeding. Although we suggest that the use of TLI should be considered carefully in patients with a history of anticoagulation, our results are not definitive to consider clotting issues to be a contraindication for the TLI technique. Although we would recommend using the TLI rather than the spray-as-you-go technique in patients at risk of secondary cervical injury, the Enk Fibreoptic Atomizer may be an effective alternative to the TLI technique because no significant differences were shown in most of the qualitative outcomes, cardiovascular stability and postoperative outcomes.
Acknowledgements relating to this article
Assistance with the study: we are particularly grateful for the scientific support and practical training from Philip C. Larson Jr., Clinical Professor at Department of Anesthesiology, David Geffen School of Medicine at UCLA, 757 Westwood Plaza, Los Angeles, CA 90095-7403, USA, and for the statistical support from Martin Mogk, MoReData (statistical office) GmbH, Kerkrader Str. 11, D-35394 Giessen, Germany and Prof. Matthias Blüher, MD, Department of Internal Medicine, University of Leipzig, Germany. Michael J. Malcharek may be contacted for requests for reprints.
Financial support and sponsorship: none.
Conflict of interest: none.
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