Fibreoptic intubation (FOI) allows endotracheal intubation in a spontaneously breathing patient and is accepted as a standard procedure for the anticipated difficult airway .
Different techniques for awake FOI have been described [2,3]. The use of oxygen insufflation and topical anaesthesia varies from expert to expert.
Oxygen can be applied via a nose probe or through the working channel of the fibreoptic device while advancing the instrument. Benumof  described the insufflation of oxygen via the working channel as ‘perhaps the best’ method while using the fibrescope. The application of oxygen via a nose probe is also recommended and commonly used .
In many institutions, lidocaine is injected through the fibrescope's working channel to achieve topical anaesthesia of both the pharyngeal and tracheal soft tissues . The technique of vaporizing lidocaine with the oxygen flow is called the ‘vaporization’ (VAP) technique.
Although the oxygen flow via the working channel may improve oxygenation of the patient, prevent fogging of the fibrescope, and blow away secretions from its tip [4,7], no prospective study has compared this technique with the standard procedure.
We hypothesized that the VAP method is faster, provides a higher oxygen saturation, and results in increased patient comfort owing to less coughing.
Material and methods
The Ethical Care Committee of the Board of Physicians Rhineland-Palatinate, Germany, had reviewed and approved the protocol of this study, and all patients gave their written, informed consent before participating in the study.
Adult nonpremedicated patients scheduled for elective surgery and requiring general anaesthesia with nasal FOI were included in the study. Patients with diseases resulting in an ASA classification greater than III or those who were pregnant were excluded. Furthermore, no oral sedative was administered prior to anaesthesia induction.
Thirty minutes prior to induction of anaesthesia, a 1 ml mixture of lidocaine 2% with phenylephrine 0.25% was applied into each nostril . After documentation of the patient's age, height, and weight, the standard monitoring, including electrocardiography, noninvasive blood pressure, and arterial oxygen saturation was initiated.
A standardized conscious sedation protocol using fentanyl (1.5 μg kg−1) and midazolam (12.5 μg kg−1) was administered to every patient. After 2 min, the FOI procedure was initiated. The same 3.7 mm fibrescope (Karl Storz GmbH & Co. KG, Tuttlingen, Germany) was used in all patients.
Thirty-four patients were randomly assigned to two groups.
FOI in the VAP group consisted of the following steps:
- Application of oxygen flow (3 l min−1) through the proximal port of the working channel (Fig. 1).
- Introduction of the fibrescope through the more patent nostril.
- Application of 2 ml of lidocaine 2% vaporized into the oxygen flow
- into the posterior naris (local anaesthesia 1)
- into the hypopharynx (local anaesthesia 2)
- on the epiglottis and the vocal cords (local anaesthesia 3)
- into the proximal trachea (local anaesthesia 4).
The procedure in the standard (STAN) group consisted of the following steps:
- Insufflation of 3 l min−1 oxygen via a nasal probe.
- Introduction of the fibrescope through the more patent nostril.
- Application of 4 ml of lidocaine 2% on the epiglottis and vocal cords (equivalent to position local anaesthesia 3) via the working channel. A maximum of 2 min was allowed for the lidocaine to take effect. The fibrescope was not passed into the proximal trachea until the glottic closure activity was judged to have been sufficiently obtunded.
- Application of 4 ml of lidocaine 2% into the proximal trachea (equivalent to position local anaesthesia 4); withdrawal of the fibrescope followed by a maximum of 2 min for the lidocaine to take effect.
After the application of the local anaesthetics, the procedure remained the same in both groups. During spontaneous ventilation, the tracheal tube (internal diameter 6.5 mm, Rüschelit tracheal tube, Rüsch, Kernen, Germany) was advanced over the fibrescope into the trachea. The correct distance of the tip of the tube in relation to the carina was measured before blocking the cuff and removing the fibrescope. General anaesthesia was then induced by 0.2 mg kg−1 etomidate.
The same anaesthesiologist being an expert in FOI performed all intubations.
Insertion of the fibrescope into the nostril was considered as the start time for all time intervals documented:
- until local anaesthesia 3
- until local anaesthesia 4
- until beginning of insertion of the endotracheal tube into the nostril
- until blocking off the cuff.
The number of coughs by the patient was documented. When coughs occurred in paroxysms, each cough was counted as one.
The description of continuous endpoints was based on nonparametric estimates (medians, quartiles) and on the graphical representation of nonparametric box plots. Nonparametric data were analysed with the Mann–Whitney test, whereas parametric data were compared with an unpaired Student's t-test. For within-group comparisons, Wilcoxon's matched pairs test was used. Owing to the observational character of the study, the P values of the tests were not adjusted for multiplicity; a P value less than 0.05 indicated local statistical significance. All numerical and graphical analyses were drawn using Microsoft Excel (for Windows XP) and SPSS (release 10.0 for Windows; SPSS GmbH Software, Theresienhöhe, Munich, Germany).
Two patients in the STAN group were excluded from the evaluation as they had received oral sedatives prior to anaesthesia induction. Fifteen patients were included in the STAN group and 17 patients in the VAP group.
There were no significant differences between the two groups with respect to age, sex, weight, and BMI (Table 1).
FOI was successful in all patients. Every patient received a total of 8 ml of lidocaine 2%. The dose of lidocaine varied between 1.72 and 3.36 mg kg−1 (median 2.42 mg kg−1).
The time needed from insertion of the fibrescope until local anaesthesia 3 (application of local anaesthetic to the epiglottis and the vocal cords) did not differ significantly in both groups. The median time was 50 s (minimum 25, maximum 120) in the STAN group and 65 s (minimum 45, maximum 121 s) in the VAP group.
The time needed from insertion of the fibrescope until local anaesthesia 4 (application of local anaesthetics into the proximal trachea) was significantly longer in the STAN group (165 s, minimum 123 s, maximum 375 s) than in the VAP group (median 125 s, minimum 75–200; P < 0.001).
The time from insertion of the fibrescope until beginning of insertion of the endotracheal tube into the nostril was significantly longer in the STAN group (307 s, minimum 150 s, maximum 500 s) than in the VAP group (median 183 s, minimum 135–247; P < 0.0001).
The time from inserting the fibrescope until inflating the cuff was also significantly longer in the STAN group (339 s, minimum 170 s, maximum 525 s) than in the VAP group (median 206 s, minimum 160–277; P < 0.0001; Fig. 2).
Prior to the start of the procedure, no difference in oxygen saturation was found between the two groups (Table 2); however, a significant (P = 0.008) decrease in oxygen saturation could be detected in the STAN group compared with the VAP group after having completed the FOI procedure.
The haemodynamic variables showed no significant differences (Fig. 3, Table 2).
The incidence of overall coughing in the STAN group was 80% compared with 59% in the VAP group. In the VAP group, no patient coughed at local anaesthesia 1 and only two patients coughed at local anaesthesia 2.
At local anaesthesia 3, the number of coughs was more in the STAN group (four coughs) than in the VAP group (one cough; P < 0.05). A significant difference (P = 0.036) was found at local anaesthesia 4 (STAN: maximum seven coughs; VAP: maximum two coughs; Table 3).
FOI is a safe technique for managing difficult airways in spontaneously breathing patients. This study was conducted to compare two commonly used techniques of applying oxygen and topical anaesthesia during FOI.
All patients were intubated successfully using both techniques; however, clear differences were evident between both methods.
The time from introduction of the fibrescope until insertion of the endotracheal tube into the nostril was 2 min longer in the STAN group than in the VAP group because, in the VAP group, the whole procedure could be continued without waiting for the local anaesthetic to take effect. Furthermore, the fibrescope in the STAN group was withdrawn after application of the local anaesthetic into the proximal trachea, which was not required in the VAP group. This time difference is statistically significant and of clinical relevance because the shorter duration of the overall procedure in the VAP group results in additional safety and comfort for the patients.
The vaporization of lidocaine into the oxygen flow during local anaesthesia 1 and local anaesthesia 2 results in topical anaesthesia of the lower airways, including the trachea. Furthermore, the volume of each dose of local anaesthetic was remarkably less in the VAP group than in the STAN group.
The use of a nasal probe to provide supplementary oxygen to the patient has proven to be sufficient , but our data highlight a potential decrease in oxygen saturation in the STAN group. In the VAP group, no patient showed an oxygen saturation of less than 99% at the end of the procedure. This provides additional safety for the patient in case of any unanticipated problems during the positioning of the endotracheal tube.
The haemodynamic variables remained stable throughout both techniques, though stimulation of the upper respiratory tract during tracheal intubation may lead to tachycardic and hypertensive responses. Therefore, the sedation protocol and both techniques of applied topical anaesthesia avoid cardiovascular stress and discomfort for the patient.
Several techniques for anaesthetizing the vocal cords and the trachea have been described previously. Each technique is characterized by specific advantages and disadvantages and, until now, no data have been available on which technique is more commonly used. The transcricoid route for applying local anaesthetics is described as safe and well tolerated by the patient . Compared with the transcricoid approach, the VAP technique is less invasive and reduces the risk of injuries. Local anaesthetics can also be applied through an epidural catheter threaded through the working channel of the fibrescope, but this is relatively costly and time consuming .
The toxic plasma concentration of lidocaine is commonly accepted as 5 mg l−1[10,11]. Therefore, the total dose of lidocaine administered during FOI is recommended to be limited to 8.2 mg kg−1. In both the STAN and VAP groups, patients received a median of 2.24 mg kg−1 lidocaine. Although reports on the application of larger doses for FOI have been published [13,14], the relatively small dose of lidocaine in our study was sufficient and did not require adaptation to the patient's weight for either technique.
The improved effect of topical anaesthesia in the VAP group is also highlighted by the reduced incidence of coughing as compared with the STAN group. This is of clinical relevance, because coughing during FOI is uncomfortable for the patient, and it makes the procedure more difficult to perform. Although it is almost impossible to adequately quantify the intensity of coughing, the incidence of coughing during FOI has been described by other authors as well. In a study using a nonstandardized conscious sedation protocol and a ‘spray-as-you-go’ technique, coughing occurred in 61.4% of patients . Ovassapian et al.  reported the quality of coughing using a cricothyroid puncture technique and reported an incidence of only 16.7% severe coughing. Coughing can also be minimized if the soft tissues are not touched with the fibrescope before adequate topical anaesthesia. As this depends on the experience of the performer, the same anaesthesiologist intubated all patients in our study.
A potential disadvantage of the VAP technique is the risk of gastric insufflation and rupture [16,17]. The risk of oxygen insufflation into the stomach is increased by a prolonged procedure, a poor view, and oesophageal intubation with the fibrescope. No data have been published on the incidence of gastric insufflation during FOI. In order to avoid gastric insufflation, this technique should be reserved for expert use only and the oxygen flow should be limited to 3 l min−1 during FOI in any of the techniques described. To vaporize lidocaine adequately, an oxygen flow of 1 l min−1 seems sufficient .
During FOI, pulmonary barotrauma may occur if the airway becomes obstructed while passing the fibrescope through a narrowed glottis in the VAP technique . As such some authors do not recommend applying oxygen through the working channel of the fibrescope . Barotrauma can be avoided by not applying oxygen flow beyond airway stenosis.
Although the view of the performer and the conditions during FOI were not part of the study, it is our belief that the oxygen flow through the working channel of the fibrescope contributed to the shorter time intervals in the VAP group. Secretions were dispersed from the lens and blurring of the view was avoided.
Keeping potential limitations of the study in mind, the results prove that the VAP technique is more advantageous than the STAN technique.
In conclusion, the results confirm our hypothesis that the ‘vaporization’ technique leads to a significantly shorter intubation time than the standard technique. Likewise, the VAP technique provides higher oxygen saturation during the procedure and a lower cough rate with increased patient comfort.
Karl Storz GmbH & Co. KG, Tuttlingen, Germany, provided the fibrescope used in this study.
This study was presented in part as a poster at the German National Congress of Anaesthesiologists 19–22 June 2004, Nuremberg, Germany.
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