Bougie-assisted difficult airway management in a manikin – the effect of position held on placement and force exerted by the tip*

Authors


  • *

    Abstract presented at an Anaesthetic Research Society Meeting, Cardiff, July 2002.

Dr I. Hodzovic, Senior Lecturer, University of Wales College of Medicine, Heath Park, Cardiff, CF14 4XN, UK.
E-mail: hodzovic@cf.ac.uk

Summary

In a randomised cross-over study, 50 anaesthetists attempted to place a multiple-use bougie in the trachea of a manikin, when holding it at either 20 cm or 30 cm from the tip. A grade 3 laryngoscopic view was simulated. The anaesthetists were blinded to success (tracheal placement) or failure (oesophageal placement). The success rates when held at 20 and 30 cm distance from the tip were 68 and 62%, respectively (p = 0.55). In a separate experiment, multiple and single-use bougies were held at four different positions and pressed onto a disc attached to a force transducer. The peak force exerted by the single-use bougies was two to three times greater than that which could be exerted by the multiple-use bougies (p < 0.0001). Holding the bougie at either 20 or 30 cm distance from the tip is unlikely to influence bougie placement. The single-use bougie is much more likely to cause trauma to tissue during placement, particularly if held close to the tip.

The multiple-use gum elastic bougie (Eschmann Healthcare Tracheal Tube Introducer, SIMS Portex, Hythe, Kent) is widely used as an aid during difficult intubation [1,2]. We could find no data in the literature investigating whether the distance held from the tip has any effect on successful placement. One study recorded the distances a bougie was held from the tip during simulated difficult intubation in a manikin, but did not primarily investigate the effect on successful placement [3]. There have been very few case reports where the bougie may have been one of the factors implicated in tissue trauma, [4–6] but there are no data on the forces that can be exerted by anaesthetists using bougies during placement.

We therefore asked 50 anaesthetists to estimate the distance from the tip they were likely to hold the bougie when faced with difficult intubation in clinical practice. The effect of holding the multiple-use bougie at 20 cm and 30 cm distance on successful placement was also investigated in a manikin set to simulate grade-3 difficult intubation. Finally, the forces exerted by the tip of multiple- and single-use bougies when held at different distances from the tip were investigated in the laboratory.

Methods

The Local Research Ethics Committee considered that ethical approval for this study was unnecessary. Fifty anaesthetists (18 consultants, 25 trainees and 7 other non-training grades) who were present in the department at the time of study, were invited to take part. The anaesthetists were informed what the study entailed and were given the choice not to participate. None declined to take part. We also recorded the name and grade of the anaesthetist, previous anaesthetic experience and previous experience with a bougie (in years). All had at least one year's experience of using bougies. The anaesthetists were asked to complete the survey questionnaire before taking part in the ‘distance study’.

Distance held survey

We surveyed anaesthetists at the Royal Gwent Hospital in Newport. The survey lasted four weeks. Each of the anaesthetists was shown a Laerdal Airway Intubation Trainer (Laerdal Medical Ltd, Laerdal Ho., Orpington, Kent, UK) set to simulate a grade 3 Cormack and Lehane laryngoscopic view, so that only the tip of the epiglottis could be seen (Fig. 1). They were then asked to write down the distance from the tip that they would routinely hold the bougie for intubation in these circumstances.

Figure 1.

The Laerdal Airway Management Trainer arranged to stimulate a Grade 3 Cormack and Lehene laryngoscopic view.

Effect of distance held on placement

The Laerdal Airway Intubation Trainer was used in this experiment. Before the start of the study, the manikin was again arranged to simulate a grade-3 Cormack and Lehane laryngoscopic view [7] and this position was not altered for the duration of the study. The laryngoscope blade (Macintosh size 3) was fixed into position using a retort stand and a clamp (Fig. 1). Ten new, unused samples of a multiple-use bougie (Eschmann Healthcare Tracheal Tube Introducer, SIMS Portex, Hythe, Kent) were used in this experiment.

Each anaesthetist made two attempts to place the multiple-use bougie in the trachea, holding it at a distance of 20 cm or 30 cm from the tip. A randomisation code ensured that equal numbers of anaesthetists held the bougie at 20 cm and 30 cm from the tip first. The randomisation code was generated according to a program written using LabVIEW (Version 2.2.1 National Instruments) running on a PowerMac Macintosh (Apple) computer. An investigator held the straight bougie at the ends and passed it to the anaesthetist. Manipulating the laryngoscope, altering the head position, or applying external laryngeal pressure, were not permitted. The anaesthetist was asked to shape the bougie to choice before attempting to place it in the trachea. A stopwatch was started after the anaesthetist had shaped the bougie. The anaesthetist placing the bougie was blinded as to whether the bougie was placed in the trachea or in the oesophagus, but this was noted by the investigator. The time taken to place the bougie was also recorded. Tracheal tube placement over the bougie was not attempted.

Force study

Five samples of a multiple-use bougie (Eschmann Healthcare Tracheal Tube Introducer) and five samples of a single-use bougie (Tracheal Tube Introducer, SIMS Portex, Hythe, Kent) were used. The multiple-use bougies were taken from the clinical environment and the single-use bougies were unused. Each bougie was held at four different positions (10, 20, 30 and 40 cm from the tip) and pressed three times onto a disc attached to a force transducer (Fig. 2) with a resolution of 0.1 N (Mecmesin PFI200N).

Figure 2.

Mecmesin PFI200N force transducer used in the ‘force study’.

A depression in the disc prevented the tip of the bougie from slipping as the bougie bent during the test. Bougies were pressed until the force recorded by the force transducer did not increase anymore (Fig. 3). The peak force for each test was recorded.

Figure 3.

Force (N) against time (s) as the bougie was pressed against the force transducer. A, bougie pressed against the force transducer; B, bougie removed.

Statistical analysis

McNemar's test was used to test the difference in placement and a paired t-test was used for testing the difference in time to position the bougie between the anaesthetists holding it at 20 and 30 cm. 95% confidence intervals were calculated using Confidence Interval Analysis software, version 2.0.0 [8]. The peak forces from the two types of bougie were compared for each distance held from the tip using the Mann–Whitney U-test. A p-value of < 0.01 was considered significant because of the multiple comparisons.

Results

Distance held survey

Fifty anaesthetists participated in the study. Twenty anaesthetists said they would hold the bougie at 20 cm, with others ranging from 10 to 40 cm and 11 not being able to specify a distance from the tip that they would hold the bougie when faced with grade 3 Cormack and Lehane laryngoscopic view (Fig. 4).

Figure 4.

Distances anaesthetists claimed to hold a bougie from the tip.

Effect of distance held on placement

Results of comparisons of success rates of tracheal placement according to the distance held from the tip of the bougie are shown in Table 1. The mean (SD) time taken for placement was significantly shorter with the 20 cm distance from the tip: 9.4 (3.6) s vs. 11.4 (4.5) s for 30 cm (Table 2).

Table 1.  Placement by 50 anaesthetists when holding the bougie at either 20 or 30 cm. Success rate when held at 20 and 30 cm was 68 and 62%, respectively. Difference (95% CI) in success rate; 6 (−7 to 19)% (p = 0.55).
Successful placement in trachea when held atNumber of anaesthetists
Both 20 and 30 cm27
20 cm only7
30 cm only4
Neither 20 or 30 cm12
Table 2.  Mean (SD) time to placement for the bougie when held at either 20 or 30 cm. Mean (95% CI) difference; 2.0 (0.7−3.3) s (p = 0.003).
Distance held (cm)Time to placement (s)
20 9.4 (3.6)
3011.4 (4.5)

Force study

An individual test result is shown in Fig. 3. For every position of holding the bougie, the peak force that could be exerted on the disc by the single-use bougies was two to three times greater than that which could be exerted by the multiple-use bougies (Table 3). The peak force decreased with increasing distance from the tip.

Table 3.  Peak force (N) that could be exerted when pressing the multiple-use and single-use bougies against the force transducer when held at different distances.
Distance held from tip (cm)Median Peak Force (N) (interquartile range [range])Mann–Whitney U-test
Multiple-useSingle-usep-value
104.410.8p < 0.0001
 (3.7–5.4 [2.9–11.1]) (10.1–11.5 [9.1–13.4]) 
201.74.8p < 0.0001
 (1.5–2.2 [1.3–4.4]) (4.1–5.0 [3.7–5.1]) 
300.92.3p < 0.0001
 (0.7–1.2 [0.6–1.9]) (2.1–2.4 [1.7–3.0]) 
400.41.2p < 0.0001
 (0.4–0.5 [0.3–0.8]) (1.2–1.3 [1.0–1.5]) 

Discussion

The distance from the tip at which most of the surveyed anaesthetists claimed they held the bougie (Fig. 4) did not differ from the actual distance anaesthetists were reported by Annamaneni et al. [3] to hold the bougie when faced with grade 3 difficult laryngoscopy (median (interquartile range) 20 (20–22) cm). Furthermore, it appears from that study that anaesthetists would choose to hold the bougie closer to the markings on the bougie (10 cm, 20 cm, 30 cm and 40 cm) than at a random distance from the tip of the bougie. But does this matter? In clinical practice most anaesthetists succeed in placing the bougie in the trachea irrespective of the distances held from the tip [1].

The difference in the success rate of tracheal placement of the gum elastic bougie when held at two distances was small and non-significant (Table 1), although the 95% confidence limit shows that success might be up to 19% better at 20 cm than 30 cm. Placement was also a little quicker at 20 cm (Table 2) but not to a clinically important extent. So there may be a slight preference for 20 cm, at least when teaching the use of the bougie.

We found that the single-use bougie was much more likely to cause trauma to tissue during placement. The peak force applied by the tip of the bougie gets progressively higher the closer to the tip the bougie is held (Table 3). The single-use bougie is also significantly less efficient than the multiple-use bougie [3,9]. The peak pressure that could be applied to the tissue by the multiple-use bougie, especially when held closer to the tip, may also be noteworthy (4.4 N when held at 10 cm distance from the tip). However, when using the multiple-use bougie, traumatic complications have been rarely reported [10]. Furthermore, the tips of the two bougies have a different appearance. The multiple-use bougie has a blunt hemisphere shaped tip, which may partially explain the low reported incidence of multiple-use bougie related airway trauma. Conversely, the single-use bougie is a plastic rod with a flat tip in the shape of a ring (Fig. 5), which may further enhance the potential to cause airway trauma.

Figure 5.

The shape of the tips of multiple-use (hemisphere) and single-use (ring) bougies.

In the ‘force study’ the multiple-use bougies were taken from the clinical environment. We believe that this reflected the clinical circumstances more closely then testing new, unused gum elastic bougies. No record was available of the number of times the bougies were re-used before they were employed in the study.

Our findings suggest that holding the bougie at 30 cm may be less likely to cause trauma with similar prospects of successful placement. However, a number of anaesthetists taking part in the study remarked that they had more control over the bougie when holding it at 20 cm, and that placement was therefore easier. Some of our anaesthetist colleagues hold the bougie near the tip (< 20 cm distance) with a hand or Magill forceps. We know of at least one anaesthetist colleague who routinely holds the bougie with Magill forceps a few centimetres from the tip in the management of a difficult airway. Holding the bougie closer to the tip may allow for more control over the distal part of the bougie and may facilitate tracheal placement.

In order to reduce the likelihood of failed bougie placement when faced with a difficult laryngoscopic view, the anaesthetist should make the following checks before the start of each operating list. Ensure that the multiple-use bougie is not too soft or too rigid [1]. Inspect the bougie closely for defects of the outer plastic coat [11,12]. Check that the angled tip of the bougie is appropriately aligned with the axis of the bougie [13]. Make certain that the bougie on the intubating trolley is the type with the angled tip, also known as the ‘coudé’ tip. The coudé-tipped bougie is much more likely to be placed in the trachea in a grade 3 laryngoscopic view than the straight-tipped bougie [14]. Lastly, avoid the single-use bougie (Portex Tracheal Tube Introducer) for the management of Grade 3 laryngeal views, because the success rate is lower when compared with multiple-use bougie [3,9].

When using the bougie it is important to obtain the best possible laryngeal view by optimizing the head and neck position [15] and/or applying optimal external laryngeal pressure [16]. The use of a McCoy laryngoscope blade may also improve the laryngoscopic view [17]. In addition, when faced with an unanticipated difficult intubation and while maintaining oxygenation, the anaesthetist should curve the bougie before attempting to place it in the trachea. Curving the bougie considerably increases the likelihood of tracheal placement [14]. The effectiveness of the bougie seems to be related to the degree of curvature (‘optimal curve’) and to the ability of the bougie to maintain the applied curved shape [14]. If this technique fails, than holding it nearer the tip may be helpful.

How many attempts should be recommended? Clinical circumstances and the skill of the anaesthetist involved should be central to the decision about the number of attempts with the bougie. If fibreoptic skills and equipment are available then the number of attempts with the bougie should be restricted. Trauma to the airway is more likely with repeated attempts. We may be reassured that traumatic complications have been rarely reported when using the multiple-use bougie [10]. The single-use bougie, on the other hand, is more likely to cause trauma and is a less effective airway adjunct [3,9].

The use of the rigid nasendoscope should facilitate intubation with the bougie in difficult circumstances [18]. Goodwin et al. have shown that the rigid ACMI (American Cystoscope Makers, Inc. Stamford, CT, USA) nasendoscope is easy to use and minimal training is required. This airway adjunct is likely to be available in any theatre suite with ENT surgery facilities. Thirty-nine of the 40 anaesthetists (98%) improved grade 4 laryngoscopic view into grade 1 or grade 2 view when using the nasendoscope [18]. The nasendoscope therefore appears to be a potentially extremely useful adjunct for unexpected difficult intubation, particularly for those without flexible fibreoptic skills.

The only commercially available bougie with characteristics similar to the ‘optimal’ bougie [14] is the Frova single-use intubating introducer (Cook (UK) Limited, Letchworth, Hertfordshire). The authors are currently testing the Frova introducer in a separate manikin study. The potential microbial [19] and prion [20] contamination of multiple-use bougie has led to a move towards single-use devices. The use of single-use bougies, however, results in both a higher incidence of failed intubation [3,9] and a greater risk of tissue trauma. This might be considered to be of more immediate importance than the risk of contamination.

Acknowledgements

We thank Emeritus Professor W. W. Mapleson for his help in preparation of this manuscript.

Ancillary