When a difficult intubation is anticipated or when intubation unexpectedly proves difficult with a rigid laryngoscope in anaesthetized patients a fibreoptic technique may be used [1,2]. However, failures of orotracheal fibreoptic intubation have been reported in up to 9.5% of cases . The equipment-related difficulties in fibreoptic intubation have been related to the design of the tip of the intubation tube, and the diameter of the insertion cord compared with that of the intubation tube [3,4].
During fibreoptic orotracheal intubation in anaesthetized patients, the pharyngeal space can be opened to facilitate fibreoptic intubation by pulling the patient's tongue or, alternatively, an oral airway can be used. The Ovassapian intubating airway (OA) (Kendall, USA) and the Berman airway (BA) (Hudson, USA) are commercially available (Fig. 1a, b). Their designs differ and therefore different techniques for exposure of the vocal cords are needed. In an earlier study comparing the Berman airway and the tongue traction method for orotracheal fibreoptic intubation the intubation times were similar . However, the ease of laryngeal exposure and intubation were not assessed.
The present study was designed to investigate the ease and time needed for exposure of the carina and for tracheal intubation when the OA and the BA were used to facilitate orotracheal fibreoptic intubation in anaesthetized patients. These intubating airways have not been compared previously.
The study protocol was approved by the hospital Ethics Committee, and informed consent was obtained from the patients. Based on a pilot study, it was estimated according to the method described by Day and Graham, that 32 patients per group were required to show with 80% power a significant difference in the intubation times between the two airways . Only patients without any upper airway pathology or abnormality, or previous intubation difficulties were included. The assessment of intubation difficulties was always subjective, including bedside tests such as the evaluation of mouth opening and neck movements. The study was randomized and for fibreoptic endoscopy each patient served as his or her own control. All intubations were performed by the authors.
After the induction of general anaesthesia with either thiopentone or propofol, one of the intubation airways (medium size Berman airway, or Ovassapian airway) was placed in the patient's mouth. The patient's lungs were ventilated by means of a facemask. The fibreoscopy was carried out when the neuromuscular block with a non-depolarizing muscle relaxing agent was found complete by train-of-four (TOF) monitoring. During the fibreoscopy the patient's jaw was held by an assistant nurse to make the visualization of the larynx possible.
The fibrescope (Olympus BF-P20D, Japan) was advanced through the airway to a depth of approximately 10 cm. The first view and the manipulations needed to visualize the vocal cords were recorded. The tip of the fibrescope was then advanced to the carina, and the time from the start of the fibreoscopy was recorded with a stop-watch. The instrument was then withdrawn and an intubation tube (Portex, UK, ID seven for women and eight for men) was mounted over the insertion cord of the fibrescope. The second airway under study was placed in the patient's mouth and the lungs were ventilated with 100% oxygen for ≈30 s. Thereafter fibreoscopy was started and similar assessments were made with this second airway. As soon as the tip of the fibrescope was close to the carina, the trachea was intubated with the airway in place. Intubation time and intubation problems, if any, were recorded. Fibreoscopy or intubation which required more than 30 s was regarded as prolonged. If intubation failed a further attempt was made with the other airway in place. The haemoglobin oxygen saturation was continuously monitored during the study period.
The χ2-test with contingency correction was used to analyse frequencies. For other analyses, Student's t-test, Mann–Whitney U-test or Wilcoxon signed rank test was used as appropriate. Correlations between the patient characteristics and fibreoscopy and intubation times were calculated. Means and standard deviations of means, or medians and extremes are presented. A P-value less than 0.05 was considered statistically significant.
Sixty-five patients were included in the study (Table 1). The airways did not differ in the duration of fibreoscopy (Table 2). The probable causes for prolonged fibreoscopies are presented in Table 3.
To visualize the vocal cords, manipulations of either the airway or the tip of the fibrescope were needed in 37 cases with the BA and in 53 cases with the OA (P<0.001). Similar first view (either mucous membrane of the oropharynx or the glottic opening) was seen with both airways in 28 cases.
The median duration of intubation was statistically but not clinically significantly longer when the BA was used compared with the OA, 10 s (5–77 s), and 8 s (4–54 s), respectively. Resistance to the intubation tube occurred in 24 cases (36%). After manipulation, intubation was successful in 21 of these (Table 4). On one occasion intubation failed with both airways, and in one case a failure to intubate with the BA in place was followed by a successful intubation with the OA in place. The durations of the fibreoscopies in these two cases were 7 s and 86 s with the BA and 20 s and 14 s with the OA. The occurrence of impingement was unrelated to the height or weight of the patient in either group. The weight of the patient correlated significantly with the fibreoscopy time with the BA (r2=0.1, P<0.05), and with the intubation time with the OA (r2=0.1, P<0.05). Five patients weighed 100 kg or more. In the BA group, fibreoscopy failed in one of these, and in one case it took 200 s. The duration in the remaining three cases was on the average 20 s. With the OA, the duration of fibreoscopy was 90 s in one case, and the cause was inadequate forward displacement of the jaw. In the remaining four patients it was 15 s.
The haemoglobin oxygen saturation immediately after intubation was on the average 98% in both groups. The lowest value observed was 95%.
Fibreoptic intubation has been advocated as a reliable technique for the management of a difficult intubation, either anticipated or unexpected [1,2]. However, in our study, intubation failed on three out of 67 occasions, and in addition, difficulties in advancing the tracheal tube occurred in 21 patients. The failure rate as well as the frequency of impingement of the intubation tube are comparable with those in other studies [3,4]. There are no reports about the incidence of unsuccessful fibreoptic intubation after a failed intubation with a rigid laryngoscope.
It is important to recognize all the factors that contribute to problems with fibreoptic intubation, and evidently these are different from those associated with a difficult laryngoscopy and intubation with the Macintosh blade . To date, in addition to an inadequate technique, only the design of the tip of the intubation tube and the size of the insertion cord of the fibrescope in relation to the diameter of the tube have been identified as causes of difficulties in fibreoptic orotracheal intubation in anaesthetized patients [1–4]. Therefore, it seemed prudent to examine the role of the intubation airways in the incidence of problems with the technique. There were two reasons for studying patients in whom a difficult intubation with a rigid laryngoscope was not anticipated. First, we hoped to exclude contributory factors other than the design of the airways. For ethical reasons we confirmed that we were able to intubate the trachea of the patient with the Macintosh laryngoscope in case the fibreoptic intubation failed.
The construction of the BA directs the fibrescope close to the vocal cords if the airway is in the midline and the BA is of adequate length. A short BA turns towards the base of the tongue and can make the visualization of the vocal cords difficult. Our results suggest that the weight of the patient contributed to the duration of fibreoscopy with the BA. However, instead of weight being predictive of difficulties we suggest that the right size of the BA is of importance for fibreoptic orotracheal intubation in anaesthetized patients. Unfortunately, we are not able to make any recommendations other than subjective assessment of the patient before choosing the size of the BA for intubation. Unlike one report , the most common reason for prolonged fibreoscopy with the OA was inadequate jaw forward displacement. Our finding can be explained by the spatula-like structure of the OA.
In the present study, there was a significant difference in the intubation times depending on the airway used, but the clinical importance of this finding is negligible. In cases with resistance to the intubation tube, the intubation times for the two groups were also significantly different. The BA, owing to its tube-like structure, must be of adequate length, but also positioned in the midline to guide the intubation tube into the trachea. A loose or missing upper incisor can turn the BA to the side, as noted in the present study. In an earier study, impingement of the tube occurred more often when a thin fibrescope was used rather than with a snuggly fitting fibrescope. The latter probably keeps the oral airway better aligned with the glottic opening . The intubation tube may get caught on the epiglottis or the arytenoid folds [2,8,9], but also on the anterior wall of the trachea (T. Randell and P. Hakala, unpublished observation). In these cases intubation can be facilitated by flexion of the neck, rotation of the intubation tube or external pressure on the larynx [2,3,8]. With the BA in place, manipulation of the BA can lead to successful intubation. The different technique needed for some cases can explain the difference observed in the intubation times when tube impact occurred. In conclusion, both airways can be used for orotracheal fibreoptic intubation in anaesthetized patients. The BA offers somewhat easier visualization of the vocal cords than the OA, provided that the BA is of an adequate size and positioned in the midline.
Upon impact of the intubation tube, manipulation of the BA may be required to complete intubation. A prolonged intubation time when compared with the OA may result.
1 Ovassapian A. Fiberoptic tracheal intubation. In: Ovassapian A, ed. Fiberoptic Airway Endoscopy in Anesthesia and Critical Care.
New York: Raven Press, 1990: 57–79.
2 Randell T, Hakala P. Fibreoptic intubation and bronchofibreoscopy in anaesthesia and intensive care. Acta Anaesthesiol Scand
3 Hakala P, Randell T. Comparison between two fibrescopes with different diameter of the insertion cord for fibreoptic intubation. Anaesthesia
4 Jones HE, Pearce AC, Moore P. Fibreoptic intubation. Influence of tracheal tube tip design. Anaesthesia
5 Smith JE, Mackenzie AA, Scott-Knight VCE. Comparison of two methods of fibrescope-guided tracheal intubation. Br J Anaesth
6 Day JS, Graham DF. Sample size estimation for comparing two or more treatment groups in clinical trials. Stat Med
7 Murrin KR. Intubation procedure and causes of difficult intubation. In: Latto IP, Rosen M, eds. Difficulties in Tracheal Intubation.
London: Bailière Tindall, 1985: 75–89.
8 Schwartz D, Johnson C, Roberts J. A maneuver to facilitate flexible fiberoptic intubation. Anesthesiology
9 Katsnelson T, Frost EAM, Farcon E, Goldiner PL. When the endotracheal tube will not pass over the flexible fiberoptic bronchoscope. Anesthesiology