A clinical evaluation of the Bonfils Intubation Fibrescope

Authors


  • Presented in part at the Anaesthetic Research Society meeting, Glasgow; April 2003

Dr M. Halligan
E-mail: mchalligan@eircom.net

Summary

The Bonfils Intubation Fibrescope is a rigid optical instrument for performing orotracheal intubation. We describe its introduction into our clinical practice in 60 patients with normal airways who required orotracheal intubation for elective surgery. Two anaesthetists each performed 30 attempts to intubate, in turn, in patients who received a standard general anaesthetic with neuromuscular blockade. Intubation was successful in 59 out of 60 cases. The median (IQR [range]) time to intubation was 33 s (24–50 [13–180] s). Median (IQR [range]) verbal rating score for difficulty was 2 (1–3 [0–10]). There was a significant correlation between the intubation times and the verbal rating score (p < 0.01). There was evidence of airway trauma in the single patient in whom intubation failed. The Bonfils Intubation Fibrescope is an effective instrument for orotracheal intubation in normal subjects.

The Bonfils Intubation Fibrescope is a rigid fibreoptic endoscope for performing orotracheal intubation, named after its designer Dr P Bonfils (Inselspital Hospital, Bern, Switzerland). It has been available on a commercial basis since 1996 (Karl Storz Endoscopy Ltd, Tuttlingen, Germany) but its use has been limited to a small number of centres [1].

Our aim was to investigate the introduction of the device into our clinical practice in terms of efficacy, time to intubation, difficulties encountered and any evidence of airway trauma.

Methods

The instrument has a long thin straight cylindrical body with a 40° curve a few centimetres from its distal end. The eyepiece is mounted at the proximal end and looks down fibre-optic bundles housed in the body (Fig. 1). Illumination is via a connecting arm to a conventional light source or portable equivalent. A tracheal tube is loaded on to the body of the instrument and is pushed into a locking device that is adjusted so the distal end of the tube is just beyond the tip of the endoscope (Fig. 2). As a result, the operator's effective view is looking out of the distal end of the tracheal tube. The shape of the instrument facilitates location of the laryngeal inlet. From this position, the operator advances the tube from the instrument through the vocal cords under direct vision. For this study, we chose to use a camera and video monitor system.

Figure 1.

The Bonfils Intubation Fibrescope, with camera and light source attached, loaded with a tracheal tube.

Figure 2.

The tip of the Bonfils Intubation Fibrescope 0.5 cm within the lumen of the tracheal tube.

South Sefton Research Ethics Committee approved the study and all participants gave written, informed consent. Sixty patients requiring tracheal intubation for elective ear, nose and throat surgery were recruited. Exclusions were a history of difficult intubation, mouth opening < 3 cm and risk of gastric aspiration. The two authors performed all the intubations, the first 30 by MH and the second 30 by PC. All the subjects were interviewed and examined at the pre-operative visit. Mallampati class as modified by Samsoon and Young [2,3], interincisor distance (at maximum mouth opening) and the thyromental distance (at maximum neck extension) were recorded.

Since there is no recognised standard technique forusing this instrument; we based our procedure on first-hand observation of a regular user of the instrument (Dr C Rudolph, University of Leipzig, Germany). Otherwise our exposure to the endoscope was deliberately limited before starting this study and we avoided practice attempts.

The patients were unpremedicated and received no antisialagogue. They lay supine with their heads in the neutral position on a small pillow. Standard monitoring including ECG, SpO2, non-invasive blood pressure, capnography and peripheral nerve stimulation were used. All patients were given intravenous midazolam 2 mg and pre-oxygenation performed for 3 min. Anaesthesia was induced with fentanyl 1 µg.kg−1, propofol 2.5 mg.kg−1 and atracurium 0.5 mg.kg−1. Thereafter, their lungs were ventilated by hand using a Bain breathing system with isoflurane 1.5% in oxygen for a further 3 min. When neuromuscular blockade was adequate as tested by train-of-four peripheral nerve stimulation, intubation was attempted.

A prepared endoscope with antifog solution on the lens and a trachael tube loaded on the body was taken in the operator's right hand, and the left hand was used to open the patient's mouth and pull the mandible forward. The chin-lift manouevre used by MH was generally effective and usually able to raise the epiglottis to expose the laryngeal inlet; PC developed this further achieving a chin-and-tongue lift with his left thumb (Fig. 3). The two authors used different techniques to advance the tip of the endoscope: MH used a midline approach using the uvula as a landmark and advanced staying in the midline until the epiglottis was reached, while PC employed a lateral approach advancing along the pharyngeal wall down to the level of the epiglottis. At the posterior pharyngeal wall the distal end was rotated in an anterior direction bring the epiglottis into view. The next step in the process was to advance the tip of the endoscope under the epiglottis (which may be adherent to the posterior pharyngeal wall). This was achieved by the following manoeuvres in a stepwise progression: chin lift; chin and tongue lift; external jaw thrust [4]; jaw thrust with maximal neck extension; and finally assistance using the Macintosh laryngoscope. At this point the tube's tip was adjacent to the vocal cords and the release of the mandible did not alter this position. The left hand (now free) was then used to guide the tracheal tube onwards under vision. The correct position of the tube was confirmed in the usual manner.

Figure 3.

Schematic diagrams showing the difference in chin-lift (MH; left) and chin-and-tongue-lift (PC; right) manoeuvres.

The starting time of the intubation attempt was taken as the moment the instrument entered the subject's mouth. At 2 min, if there was no success, an assistant performed external jaw thrust by applying pressure at the angle of the mandible. Completed time to intubation was not recorded until it was confirmed by capnography. The maximum time allowed for each intubation attempt was 3 min. A fall of SpO2 below 92% was a further criterion for abandoning the intubation attempt. Conventional laryngoscopy was used to check for the presence of bleeding or other injury when endoscopic intubation was successful, or to perform tracheal intubation in the case of failure.

We documented difficulty by means of a Verbal Rating Score (VRS; 0–10). This was influenced by patient factors, poor intubation technique and equipment factors. Freehand text notes were made at the time to explain these difficulties further. The relationship between the VRS and time to intubation was tested using the Pearson correlation coefficient.

Results

Characteristics of the patients studied are shown in Table 1. In all patients, SpO2 remained satisfactory (> 92%) at all times. Endoscopic intubation was successful in 59/60 attempts, with median (IQR [range]) time to intubation for the 59 subjects 33 s (24–50 [13–180] s). The sequence of times taken for the individual anaesthetists is shown in Fig. 4. Median (IQR [range]) time to intubation by MH in 30/30 was 44 s (32–55 [24–180] s) and by PC in 29/30 was 25 s (20–30 [13–86] s). The single failure was the only patient with any trauma to the airway. Minor difficulties, although frequent, were easily overcome and are summarised in Table 2. Median (IQR [range]) VRS for difficulty for the 60 subjects was 2 (1–3 [0–10]). There was a significant correlation between intubation time and VRS (p < 0.01). External jaw thrust was used in three cases and gave an advantage in two. Maximal neck extension was used on one occasion and was effective. The Macintosh laryngoscope was not required in any cases.

Table 1. Characteristics of patients undergoing attempted orotracheal intubation using the Bonfils Intubation Fibrescope, by two different investigators (MH and PC). Values are mean (SD) or number (%).
  MH
(n = 30)
PC
(n = 30)
Age; years33 (14)37 (15)
Weight; kg72.6 (15.5)81.0 (14.4)
Sex; M:F21 : 920 : 10
ASA Grade:
 126 (87%)25 (83%)
 2 4 (13%) 5 (17%)
 > 2 0 0
Mallampati Class:
 127 (90%)23 (76%)
 2 3 (10%) 5 (17%)
 3 0 2 (7%)
 4 0 0
Thyromental distance; cm 9.3 (1.5)10.2 (1.2)
Interincisor distance; cm 5.1 (0.6) 5.2 (0.8)
Figure 4.

Intubation times for patients undergoing attempted orotracheal intubation using the Bonfils Intubation Fibrescope, by two different investigators: MH (♦) and PC (▪) [in one patient (•) the attempt failed].

Table 2. Difficulties encountered in 60 patients undergoing attempted orotracheal intubation using the Bonfils Intubation Fibrescope.
  • *

    Antifog solution used from n = 14 onwards.

Patient factors:
 Secretions reducing view18 (30%)
 Difficulty getting scope tip under epiglottis12 (20%)
 Heavy immobile mandible4 (7%)
 Teeth; prominent incisors/crowns3 (5%)
 Large tonsils reducing view3 (5%)
 Edentulous; slight mandible1 (2%)
Instrument/User factors:
 Fogged lens* reducing view 
 Tube not loaded properly reducing view3 (5%)
 Tangled light cable2 (3%)
 Trolley too high1 (2%)
 Camera loose1 (2%)
 Incorrect hand grip1 (2%)

Discussion

In this small number of patients without anticipated difficulty, orotracheal intubation with the Bonfils Intubating Fibrescope was achieved in all but one. The relative ease in achieving intubation is reflected not only in the short intubation times but also in the low VRS for difficulty. It was clear however, that the use of this endoscope is not intuitive and a learning process was evident from an early stage. Indeed, the failure with PC's first case supports this assertion. A previous report of these data looking at the intubation times suggested a learning experience of 20–25 cases [5]. We have not attempted to compare the two authors' results formally because this was not planned as part of the initial protocol and the intubation techniques evolved during the course of the study. The second operator (PC) had the advantage of witnessing all of the first 30 attempts before commencing his 30 cases.

Creating space in the oropharynx for the instrument and lifting the epiglottis is an important aspect of its use. If the epiglottis is not lifted clear of the posterior pharyngeal wall, it is possible to use the endoscope as a rigid stylet, and sweep under the epiglottis and lift it forward to expose the laryngeal inlet. Similarly, it can be used to displace soft tissues such as large tonsils to one side as required. Others have advocated the use of the Macintosh blade in combination with the endoscope in patients whos tracheas are difficult to intubate [1], although we did not use the Macintosh laryngoscope to assist us with any of our subjects.

While it is possible to advance the endoscope some distance below the glottis into the trachea before releasing the tracheal tube, this is not recommended as it may be increase the risk of trauma, and was not practised in this study. Upper airway trauma in normal patients after direct laryngoscopy with a Macintosh blade has been reported between 5% to 6.9%[6,7]. Where a view of the glottis is limited, resulting in increased physical force and repeated intubation attempts, trauma is reported up to 17%[6]. Difficult or awkward intubation represented approximately 4.3% of cases in one large Canadian study [8]. Minimal trauma to the airway is one of the advantages claimed for the endoscope. This is supported by this study, as there was no evidence of bleeding or trauma other than in the one failed intubation (1.7%). Advancement of the tube under direct vision would be expected to avoid some of the complications associated with intubation using blind stylet devices [9].

It is inevitable that some comparisons will be made with flexible fibre-optic laryngoscopes. It seems probable that the learning time for orotracheal intubation is shorter for the Bonfils endoscope than for fibre-optic nasotracheal intubation [10]. The Bonfils scope is more robust and gives a larger and clearer image but with similar distortion. Although oral secretions were noted in 18/60 subjects (30%), the difficulty they caused was minor and they did not result in failed attempts; premedication with anticholinergic drugs is therefore unnecessary. Railroading of the tracheal tube is more straightforward than with the flexible fibreoptic laryngoscope [11]. The instrument is however, not suitable for nasal intubation. The configuration of its injection port and working channel does not allow a wire to be passed as a guide for catheters/tracheal tubes, as has been described for flexible fibrescopes [12]). We have no experience using the endoscope for awake intubation but this is possible [1].

There are many other optical laryngoscopes and stylet intubation devices available. The Bullard laryngoscope (Circon ACMI, Stamford, Connecticut, USA) has a curved blade that elevates the epiglottis directly and permits a view of the laryngeal opening. It has also been advocated for situations in which little or no neck movement is appropriate, for example in cases of cervical spine injury [13]. The UpsherScope (Mercury Medical, Clearwater, Florida, USA) [14] is somewhat similar to the Bullard but its blade's tip is placed in the valleculum, and the WuScope (Pentax Precision Instruments, Orangeburg, New York, USA) [15] has a similar design concept. These laryngoscopes may feel familiar to anaesthetists because their blade incorporates the ‘Macintosh curve’ but difficulties have been noted when advancing tracheal tubes, largely because the view is ‘off field’ compared with the central of view obtained with the Bonfils device. Lightwands are similar in shape to the Bonfils endoscope but are blind intubating devices. Other fibreoptic stylets are designed for use with conventional laryngoscopes [16].

The clinical role for the Bonfils endoscope, particularly in respect of difficult intubation, has yet to be determined, but some speculation based on our limited exposure is reasonable. We have become progressively more impressed with its effectiveness over time. The view from immediately above the glottis and into the subglottis is very impressive when compared with conventional laryngoscopy. Because less postural adjustment is necessary it may have advantages for patients with limited cervical spine movement. Others have suggested it may have a role in unanticipated difficult intubations [1]. Finally, the authors believe that clinical experience with the device is critical and that training with currently available manikins is of limited use.

Acknowledgement

We are grateful to Karl Storz Endoscopy Ltd for supplying the Bonfils Intubation Fibrescope.

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