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Summary

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Conflict of interest and financial support
  7. References

Ten volunteers evaluated the performance of four currently available manikins: Airway Management TrainerTM, Airway TrainerTM, Airsim and Bill 1 as simulators for the 16 procedures described in the Difficult Airway Society Guidelines (DAS techniques) and eight other advanced airway techniques (non-DAS techniques), by scoring and ranking each manikin and procedure. Manikin performance was unequal (p < 0.0001 for both SCORE and RANK data for both DAS and non-DAS techniques). Post hoc analysis ranked the manikins for DAS techniques as: 1st Laerdal, 2nd Trucorp, 3rd equal VBM and Ambu. For non-DAS techniques, the ranking was: 1st equal Laerdal and Trucorp, 3rd equal VBM and Ambu. The power to discriminate for individual procedures was considerably lower but for 15 of 16 DAS techniques and 6 of 8 non-DAS techniques, manikin performance differed significantly. Post hoc tests showed significant performance differences between individual manikins for 10 DAS procedures, with the Laerdal manikin performing best.

Manikins are widely used to teach a variety of skills to medical personnel and professions allied to medicine. These manikins vary in design and complexity depending on the scenarios or techniques that they are used to simulate. The use of manikins may be particularly relevant when teaching or learning skills that are not routine, such as those required in an emergency. Airway difficulties in anaesthesia are uncommon and, for practical and ethical reasons, use of manikins as part of a programme to learn and practise these skills has advantages. Since the publication of the Difficult Airway Society guidelines (DAS) in 2004 [1], manikins bought by anaesthetic departments are likely to be used as simulators for teaching the techniques listed in these guidelines. The most suitable manikin for learning such skills is not clear. We have evaluated four recently available manikins, all described as suitable for teaching supraglottic airway insertion, to determine their adequacy as simulators for teaching these guidelines. In addition, we have also evaluated the utility of these manikins for teaching advanced airway skills that are not listed in the DAS guidelines.

Materials and methods

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Conflict of interest and financial support
  7. References

The study was given approval by the local Research Ethics Committee. Each volunteer gave written consent to participate in the study.

We evaluated the performance of four new manikins (Fig. 1, Table 1) as simulators of all non-surgical airway management techniques present in the DAS guidelines (‘DAS techniques’) [1] and other advanced airway techniques (‘non-DAS techniques’):

image

Figure 1.  Airway manikins studied.

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Table 1.   Details of airway manikins used for inserting supraglottic airway devices.
 Airway Management Trainer Airway TrainerBill 1' Airway Airsim Management Simulator
  • *

    Resusci-Anne head released as prototype.

  • For head to attach to existing Resusci-Anne manikin/for head with electronic sensors for use with recording Resusci-Anne manikin.

Date releasedFebruary 2005December 2004*March 2005December 2004
ManufacturerAmbu Ltd. Burrel Road,  St Ives, Cambridgeshire  PE27 3LELaerdal Medical, Stavanger,  NorwayTrucorp Ltd, Whitla Medical  Building, 97 Lisburn Road,  Belfast BT9 6JQVBM Medizintecknik GmbH,  Einsteinstrasse 1, D-72172 Sulz,  Germany
Approximate cost; £ (€)600 (871)600 (871)/800 (1162)1200 (1743)1250 (1816)
  • • Airway Management TrainerTM (Ambu, St Ives, UK);

  • • Airway TrainerTM (Laerdal, Stavanger, Norway);

  • • Airsim (Trucorp, Belfast, Northern Ireland);

  • • Bill 1 (VBM, GmbH, Sulz, Germany).

The manikins are referred to by their manufacturers' names.

DAS techniques were: 1) bag valve mask ventilation, 2) chin lift, 3) jaw thrust, 4) intubation with a Macintosh laryngoscope blade, 5) intubation with a straight laryngoscope blade, 6) intubation with a McCoy laryngoscope blade, 7) simulation of a grade 3 laryngoscopy [2], 8) gum elastic bougie use (GEB) (we used a reusable GEB, Smith's Medical, Hythe, UK), 9) application of optimal external laryngeal manipulation/backwards upwards rightwards pressure, (10) application of cricoid pressure, 11) insertion and ventilation with an LMA Classic (Intavent Orthofix, Maidenhead, UK), (12) insertion and ventilation with an intubating laryngeal mask airway (ILMA) (Intavent Orthofix), 13) insertion and ventilation with an LMA ProSeal (PLMA) (Intavent Orthofix), 14) insertion and ventilation with a Combitube (Tyco Healthcare, Gosport, UK), 15) fibreoptic intubation via an LMA Classic, and 16) fibreoptic intubation via an ILMA.

Non-DAS techniques were: 1) oral fibreoptic intubation, 2) nasal fibreoptic intubation, 3) blind intubation via an ILMA, 4) intubation with a lighted stylet (we used a Trachlight; Laerdal), 5) intubation with an optical stylet (we used a Shikani optical stylet; Timesco, London, UK), 6) PLMA insertion over a GEB, 7) orogastric tube (OGT) insertion via a PLMA, 8) fibreoptic-guided placement of an Aintree intubating catheter (Cook Critical Care, Letchworth, UK) via an LMA Classic.

Single-use (Combitube, face masks, tracheal and orogastric tubes, Aintree intubation catheter) and limited-reuse devices (GEB, Trachlight) were used throughout the study, provided there were no external signs of damage or malfunction. There were no failures of these devices.

Ten volunteer anaesthetists, of specialist registrar or consultant grade, performed each technique once in each of the manikins. The order in which the manikins were tested was randomised using opaque envelopes containing a card with the name of each manikin. Each procedure was scored by the anaesthetist in each manikin. For most procedures this was scored as: 2 = able to perform and lifelike, 1 = able to perform, 0 = not able to perform [3]. For insertion of the LMA Classic, ILMA and PLMA, measures of correct position were also scored. These were easy insertion, ‘end point’ to insertion, correct clinical position with posterior line in midline, rising up with inflation (not scored for the PLMA) and ability to ventilate: each scored: 1 = yes, 0 = no. GEB insertion was scored out of 3 (one point each for the presence of clicks, hold-up and rotation during insertion). To ensure even weighting for techniques, the scores for each procedure were divided to give a maximum score for each procedure of 2.

The primary outcome measure sought was the overall performance of each manikin as a simulator for the non-surgical techniques listed in the DAS guidelines, secondary outcome measures were the performance of the manikin for each of the individual techniques in the DAS guidelines, and also for non-DAS techniques. Statistical analysis of manikin performance for simulation of DAS techniques and non-DAS techniques was performed separately. Friedman's anova was used to detect a difference in performance within the group of manikins. Where p < 0.05 post hoc analysis was performed using Wilcoxon signed rank testing, corrected for multiple comparisons, to determine performance differences between individual manikins. A corrected p value of < 0.05 was taken as significant. Individual techniques were analysed identically.

Comments from participants were not actively sought but were noted when made.

Results

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Conflict of interest and financial support
  7. References

Analysis of overall performance was significantly different between manikins for DAS techniques (p < 0.0001) and non-DAS techniques (p < 0.0001). Post hoc analysis showed significant differences between manikins, favouring Laerdal and Trucorp compared to VBM and Ambu (Table 2). Rankings, using only statistically significant performance differences, are as follows:

Table 2.   Overall performance of each manikin.
 AmbuLaerdalTrucorpVBM
  • DAS techniques scores: Friedman p < 0.0001; post hoc tests: Laerdal vs Ambu, Trucorp and VBM: all p < 0.001*, Trucorp vs Ambu and VBM: both p < 0.005*. Ambu vs VBM: p not significant.

  • Non-DAS techniques: Friedman p < 0.0001; post hoc tests, Trucorp vs Ambu and VBM: both p < 0.005*, Laerdal vs Ambu and VBM: both p < 0.005*.

  • Laerdal vs Trucorp: p not significant. Ambu vs VBM: p not significant

  • *

    p corrected for multiple comparisons.

DAS
 Sum of scores126224162129
 Mean0.81.41.00.8
 Median1211
Non DAS
 Sum of scores719710075
 Mean0.91.21.30.9
 Median1111
  • • DAS techniques: 1st Laerdal, 2nd Trucorp, 3rd and 4th VBM and Ambu. (Differences between VBM and Ambu were not statistically significant).

  • • Non-DAS techniques: 1st and 2nd Laerdal and Trucorp, 3rd and 4th VBM and Ambu. (Differences between Laerdal and Trucorp, and between VBM and Ambu were not statistically significant).

Individual procedures

The power of this analysis to detect performance differences for individual procedures was considerably lower than for ‘overall performance’ of DAS techniques and non-DAS techniques. Analysis showed performance differences between manikins in 15 of 16 DAS procedures and in 6 of 8 non-DAS procedures. Post hoc tests are presented for DAS techniques in Table 3 and for non-DAS techniques in Table 4. For DAS techniques, post hoc testing showed significant performance differences between individual manikins in 10 of 16 procedures (Table 3). Laerdal scored best in 13 of 16 procedures and significantly better than VBM and Ambu for seven. Trucorp scored best or second in 11 of 16 DAS procedures and was significantly better than VBM and Ambu for three procedures (Table 4). Post hoc analysis did not reach significance for any individual non-DAS procedures.

Table 3.   Individual (DAS) techniques.
Procedure1st ranked2nd rankedFriedman p < 0.05? Significant post hoc test
  1. A, Ambu; L, Laerdal; T, Trucorp; V, VBM.

  2. BVM, bag mask valve; GEB, gum elastic bougie; OELM/BURP, optimal external laryngeal manipulation/backwards upwards rightwards pressure; cLMA, LMA Classic; ILMA, intubating LMA; PLMA, LMA ProSeal.

  3. ‘Friedman p < 0.05’ indicates a significant performance difference within the group of manikins.

  4. ‘Significant post hoc test indicates corrected p < 0.05 in direct comparison between individual manikins.

BVMLVYesL > A, L > T, L > V, T > A, V > A
Chin liftLTYesNone
Jaw thrustLAYesL > T, L > V, A > V, T > V
IntubationLTYesL > A, L > V
Grade 3 viewTAYesT > l, T > V
GEB useLTYesL > A, L > T, L > V
Cricoid pressureLVYesL > T
OELM/BURPLAYesNone
cLMA insertionLVNon/a
Fibrescope via LMAL and TYesL > A, L > V, T > A, T > V
ILMA insertionLA and TYesNone
Fibrescope via ILMATLYesT > A, T > V
PLMA insertionLA, T and VYesL > A, L > T, L > V
Combitube insertionLTYesL > A, L > T, L > V
Straight bladeLTYesNone
McCoyLTYesNone
Table 4.   Individual (non-DAS) techniques.
Procedure 1st ranked 2nd ranked Friedman p < 0.05?Significant post hoc test
  1. A, Ambu; L, Laerdal; T, Trucorp; V, VBM.

  2. ILMA, intubating LMA; PLMA, LMA ProSeal; GEB, gum elastic bougie; OGT, orogastric tube, AIC, Aintree intubating catheter.

  3. ‘Friedman p < 0.05’ indicates a significant performance difference within the group of manikins.

  4. ‘Significant post hoc test indicates corrected p < 0.05 in direct comparison between individual manikins.

Oral fibreoptic intubationTLYesNone
Nasal fibreoptic intubationTLYesNone
Blind intubation via ILMATLYesNone
Trachlight intubationTVYesNone
Seeing optical styletTLYesNone
PLMA over GEBLTYesNone
OGT via PLMALVNoNone
Fibreoptic AIC placementLVNoNone

Discussion

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Conflict of interest and financial support
  7. References

In this study we asked experienced anaesthetists to semi-objectively assess the adequacy of these manikins for simulating a variety of advanced airway techniques. Individual procedures were marked 0–2 and performance differences when using such a narrow scoring system are likely to represent clinically relevant differences. The scoring system we used tested both the feasibility of performing a procedure with a particular manikin, and the rather more complex (and subjective) assessment of whether performance of that procedure was lifelike. We believe that this scoring system will ensure that those manikins performing higher for a procedure, or group of procedures, will genuinely be better simulators and have a higher utility in practice.

We have clearly shown that manikin performance is unequal and the manikin most suitable or lifelike may vary according to the techniques being simulated. If wishing to use a single manikin for training the DAS guidelines, the Laerdal manikin performs best and the Trucorp manikin also performs better than those from VBM and Ambu. The Laerdal and Trucorp manikins were also preferable for simulating the non-DAS techniques that we examined.

When the techniques are broken down into individual procedures our study was less well powered to detect differences in performance. Despite this, for 21 of 24 individual procedures examined, we found significantly different performances between manikins. Further, in 10 of the 16 procedures making up the DAS techniques we were able to determine the more preferable manikins. In all these cases the Laerdal manikin was ranked best, with the Trucorp manikin frequently ranking second. The Laerdal and Trucorp manikins were often numerically favoured even in those procedures where a statistically significant difference in manikin performance was not reached.

There were many comments from the volunteers about aspects of manikin performance and design. The Ambu manikin was most criticised for the rigidity of the ‘tissues’, poor laryngeal anatomy and for having a sagittal split (a large portion of the neck is missing): this may be useful for teaching airway anatomy but means that it is impossible to ventilate the manikin in some circumstances and allows misplacement of supraglottic airways and laryngoscopes. The Laerdal manikin received little criticism except for having poor nasal anatomy. The Laerdal manikin is not designed specifically for intubation, or ‘subglottic’ work, but participants did not comment adversely on its performance in this regard. There were several comments about the high quality of the simulated internal anatomy of the Trucorp but also several negative comments about its unlifelike external appearance. There were also negative comments about poor facemask ventilation and concerns over the robustness of the simulated tissues, though this was not evaluated. The VBM manikin was mainly criticised for its stiff tissues and unrealistic laryngeal anatomy.

The study has limitations. Firstly, although we used the most recent versions available for each manikin at the time of the study they may have been modified further since our study was conducted in March 2006. Secondly, we evaluated only one of each manikin and we cannot exclude the possibility of variations between individual manikins from the same manufacturer. We have not examined consistency of manikin performance over a prolonged period nor manikin durability. Thirdly, we have not performed any formal comparison of cost (Table 1), portability or other features which may affect a department's choice.

We have now performed four studies with these manikins. We found the VBM and Trucorp manikins best for simulation of LMA Classic insertion with the Laerdal manikin also adequate [4]. We found the Laerdal and Trucorp manikins best for insertion of a wide variety of (non-laryngeal mask) supraglottic airways [5] and we found the VBM manikin best for insertion of single use laryngeal masks, though in this study all manikins were adequate [6]. With this study we can now conclude the Laerdal Airway Trainer and Trucorp Airsim manikins are both suitable for simulating a wide variety of more advanced airway management procedures, including simple and advanced techniques included in the Difficult Airway Society Guidelines.

Conflict of interest and financial support

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Conflict of interest and financial support
  7. References

This study was supported by a grant from the Difficult Airway Society, which purchased two of the manikins (VBM and Ambu). The manikin from Trucorp was donated to the study and that from Laerdal loaned for the period of the study. TMC has participated in informal evaluation of Laerdal equipment for the company. He has also received payment for lecturing from Intavent Orthofix and the LMA Company, both of which manufacture laryngeal mask airways. Some of the equipment used in the study was donated by manufacturers either free of charge or at cost price.

References

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Conflict of interest and financial support
  7. References