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Keywords:

  • Tracheotomy;
  • patient simulation;
  • emergencies

Summary

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

This study used a patient simulator to study the ease of use and efficacy of four currently available cricothyroidotomy sets. We assessed the success of insertion of each piece of equipment and measured the subsequent adequacy of oxygenation and ventilation. We also examined the complications encountered using each set. We found that there was a 100% success rate of achieving an adequate airway within acceptable time limits using the ‘Quiktrach’ and ‘Melker’ sets, with good airway patency and ease of ventilation. There was an unacceptably high failure rate in achieving a patent airway when using the ‘Transtracheal airway catheter with ENK-flow modulator’ and ‘Patil's airway'. The pre-assembled and user-friendly ‘Quiktrach’ set provided the fastest and most effective means of oxygenation in the simulated patient requiring an emergency surgical airway.

Failure to establish a patent upper airway by nonsurgical means is a rare complication in anaesthesia and emergency care. In such a situation, emergency cricothyroidotomy is an established and life-saving technique for providing effective lung ventilation and oxygenation. However, emergency cricothyroidotomy is performed infrequently and, when necessary, can prove difficult because of a lack of both training and skill retention. In an urgent or unplanned attempt to obtain airway control, success is less likely and complications are more common [1]. However, clinicians continue to gain experience with invasive airway equipment only in a dire emergency, where time is a crucial factor. In such situations their theoretical knowledge, training and previous experience provide the cornerstones of successful management of the crisis.

It is unethical and impractical to provide training and to perform studies in a real ‘life and death’ situation. In the past, studies have been performed on cadavers [2], inanimate mannequins [3] and pig larynxes in order to compare the efficacy of different cricothyroidotomy sets. The conclusions of these studies cannot be reliably extrapolated to live patients. These studies have attempted to compare the efficacy of different emergency airway equipment. However, they were unable to assess the ability to oxygenate the patient, to ventilate the patient's lungs and to achieve subsequent time-related changes in alveolar and blood gases. Moreover, these studies made no attempt to reproduce the psychological time pressure and sense of crisis occurring during an episode of profound desaturation that might influence an anaesthetist's actions. In order to overcome these drawbacks, we used a human patient simulator for the assessment of cricothyroidotomy equipment. The scenario used in the study mimicked a real-life episode of profound arterial desaturation, when the anaesthetist was asked to perform a cricothyroidotomy with a given set, and when there was no time to be trained or to read instructions. The simulator thus provided us with the opportunity to evaluate the efficacy of each device in an emergency situation without endangering humans or animals.

Methods

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Our local research ethics committee waived the need for approval in view of the fact that the study was not performed on patients and the human subjects were anaesthetists who were given the opportunity to decline to participate.

The human patient simulator used was the ‘METI Simulator’. (Medical Education. Technologies Inc, FL, USA. Website: http://www.meti.com) (Fig. 1). The simulator parameters used throughout the study are given in Table 1. The METI adult human patient used in this study is a life-size computer-controlled mannequin that breathes, has a heartbeat and includes sophisticated modelling of cardiorespiratory physiology and pharmacology, enabling it to mimic human physiological responses accurately. The system comes with a number of preconfigured ‘patients’, in which the underlying physiological model is tailored to duplicate different clinical presentations. A continuous, real-time presentation of arterial blood pressure, oxygen saturation, and alveolar and arterial blood gas values is displayed. The simulator has a puncturable and replaceable cricothyroid membrane, which is made from a double-layered plastic tape to give a consistency comparable with the cricothyroid membrane. This ‘membrane’ was replaced after every attempt. The simulator appears to consume oxygen and produce carbon dioxide using interlinked gas tanks that are controlled by the computer-generated physiological model.

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Figure 1. The human patient simulator.

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Table 1.  Human Patient Simulator parameters.
ParameterValue
Patient weight70 kg
Functional residual capacity2000 ml
Respiratory quotient0.8
Oxygen consumption200 ml.min−1
Fixed neuromuscular blockade100%
AirwaySwollen tongue and oropharynx
Shunt fraction50%
Cardiac rhythm overrideSinus

The simulator system permits accurate continuous measurement of the partial pressures of oxygen, carbon dioxide and nitrogen in the mannequin's lungs. These partial pressures vary according to parameters set via the respiratory model, the actual minute ventilation of the mannequin's lungs and the gaseous composition of the inspired gas. Arterial blood gas values and arterial saturation are mathematically derived from these measured values. Application of a shunt fraction to the model allows the simulation of hypoxaemia by artificially depressing Sao2 without affecting measured PAo2. This creates a sense of clinical urgency within the scenario detailed below. Laryngospasm was deliberately not set in order to allow passive exhalation.

The four cricothyroidotomy sets used were. Quiktrach (VBM Medizintechnik GmbH, Germany) (Fig. 2); Patil's Airway (Fig. 3); the Transtracheal airway catheter with open ENK oxygen flow modulator (Fig. 4); Melker's (Fig. 5)– the last three sets all from Cook Ltd, UK. The sizes of the four sets were chosen so as to have similar dimensions available (Table 2). Ten experienced anaesthetists (consultants or specialist registrars in their fifth year of training) volunteered to perform cricothyroidotomies on the patient simulator. The subjects had no prior information about the scenario and were unfamiliar with all four sets before the study. None of them had had any specific training in performing a cricothyroidotomy. All 10 anaesthetists were presented with the same scenario. They were told that a 70-kg male patient without any cardiovascular or respiratory disease required an emergency surgical airway after all attempts to oxygenate the lungs by conventional means had failed, and that neuromuscular blocking drugs had been given to the patient. Each anaesthetist repeated the trial using all four different cricothyroidotomy sets selected in random order. The sets were reused if they were not damaged.

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Figure 2. Quiktrach cricothyroidotomy kit.

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Figure 3. Patil's Airway.

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Figure 4. Transtracheal airway catheter with ENK flow modulator. (1) Transtracheal airway catheter. (2) ENK flow modulator. (3) Oxygen tubing.

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Figure 5. Melker's cricothyroidotomy kit.

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Table 2.  Cricothyrotomy set sizes.
 Melker'sQuiktrachTranstracheal Airway CatheterPatil's Airway
Internal diameter; mm4423
Length; mm42425060

Before each test run the simulator model was rebooted to preclude the influence of previous interventions, was then activated, calibrated and connected to its monitoring devices. These included noninvasive blood pressure, ECG, Sao2 and FÉco2. Neuromuscular blockade was then set at 100%. When arterial oxygen saturation decreased to 80%, the anaesthetist was handed one of the four sets. Each candidate was permitted 5 min after desaturation to 80% to perform a cricothyroidotomy with the set. An oxygen flow of 15 l.min−1 was allowed for each cricothyroidotomy set, with or without a self-inflating bag. The time required to achieve patent airway and for PAo2 to exceed 13.3 kPa was noted. We also noted the correct positioning, patency and ease of insertion, fixation and ventilation (Table 3). The alveolar partial pressure of oxygen was measured as a direct variable and was considered to be the indicator of successful oxygenation rather than the monitored Sao2 value, which was decreased by the set shunt factor. We also noted complications such as trauma, kinks, leakage and damage to the cannula. Correct placement of the cricothyroid cannula was confirmed by the exhaled carbon dioxide trace on the monitor.

Table 3.  Observations made.
1. Time to achieve patent airway with each of the four individual sets 
2. Time taken to achieve PAo2 > 13.3 kPa 
3. Correct positioningYes/No
4. PatencyYes/No
5. Easy insertionYes/No
6. Easy ventilationYes/No
7. Easy fixationYes/No
8. Complications (injury to surrounding structures)Yes/No
9. Set preference expressed by anaesthetist 

At the end of each series of tests, the anaesthetists were asked which set they would prefer to use clinically and whether participating in this study would make them feel more confident if they had to perform a cricothyroidotomy. We also compared the costs incurred in using each set. Statistical analysis was performed with Friedman's test to compare the success rate to achieve a patent airway and with Cochrane's test for comparing the times to achieve PAo2 > 13.3 kPa.

Results

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

The computer program worked as expected and produced a realistic display. No simulation was abandoned. The simulator was easy to use and presented the patient's condition realistically. The experiment successfully created a feeling of urgency in the anaesthetists.

There was 100% success rate in correct placement with the Quiktrach and Melker's sets with good airway patency and ease of ventilation (Table 4). A carbon dioxide trace was clearly produced on the monitor with both these sets. Although the Transtracheal Airway Catheter set appeared easy to insert, only 4/10 of the catheters were correctly placed. Patil's Airway was difficult to insert, although 6/10 of the sets were eventually placed correctly.

Table 4.  Success of positioning and ease of insertion, ventilation and fixation when using the four sets.
  Melker's (n = 10)Quiktrach (n = 10)Transtracheal Airway Catheter (n = 10)Patil's airway (n = 10)
Correct positioning101046
Easy insertion101093
Easy ventilation101012
Easy fixation101004

A patent airway was achieved in a median time of < 60 s with Melker's and Quiktrach sets. In those simulations in which a patent airway was achieved with the other two sets, the median time to achieve a patent airway was >100 s (Table 5). The median [range] time taken to achieve a PAo2 > 13.3 kPa was 58 [50–86] s with the Quiktrach set and 130 [111–180] s with Melker's set but was > 140 s with the other two sets.

Table 5.  Success and time taken to achieve a patent airway and PAo2 > 13.3 kPa. Values are number or median [range].
 Melker's (n = 10)Quiktrach (n = 10)Transtracheal Airway Catheter (n = 10)Patil's Airway (n = 10)
Success in achieving a patent airway1010108
Time taken to achieve a patent airway; s38 [30–54]51 [42–73]102 [75–116]123 [74–147]
Success in achieving PAo2 > 13.3 kPa101046
Time taken to achieve PAo2 > 13.3 kPa; s130 [111–180]58 [50–86]185 [85–329]140 [115–210]

The Quiktrach set proved to be the easiest to fix to the patient; the Transtracheal Airway Catheter set was the most difficult.

There was evidence of trauma to the posterior tracheal wall (puncture marks and tears) in 2/10 of each of the sets (Table 6). There was damage to the cricoid and thyroid cartilages during one subject's use of the Quiktrach set. Kinking, system leaks and cannula damage occurred in up to 30% of Transtracheal Airway Catheter sets and Patil's Airways. Re-insertion was necessary in 30% of the simulations with the Transtracheal Airway Catheter set and Patil's Airway.

Table 6.  Complications.
 Melker's (n = 10)Quiktrach (n = 10)Transtracheal Airway Catheter (n = 10)Patil's Airway (n = 10)
Trauma to posterior tracheal wall2222
Trauma to surrounding soft tissues0100
Kinking0033
Leak in the system0030
Re-insertion0033
Damage to cannula0033

When asked for their choice of set for general use in the hospital, 60% of the candidates preferred the Quiktrach set, the other 40% choosing Melker's set because of their familiarity with the Seldinger technique involved in its insertion. The subjects felt that their performance had improved as a result of participation in the study. The costs of the sets are as follows: Quiktrach = £75.00; Melker's = £58.20; Transtracheal Airway Catheter = £70.80; Patil's Airway = £34.20.

Discussion

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

When faced with a failed intubation, cricothyroidotomy is a favoured method of emergency airway access. When compared with tracheostomy, it is faster, simpler, less invasive and less likely to cause haemorrhage. The procedure relies on easily visible surface landmarks and needs less neck extension than tracheostomy. The high morbidity and mortality associated with emergency tracheostomy makes it undesirable for gaining emergency airway control. However, emergency cricothyroidotomy is performed infrequently and often under life-threatening situations. It has been shown that only 14% of anaesthetic departments provide formal training in failed intubation and cricothyroidotomy [4]. Thus, if an anaesthetist is forced to perform a cricothyroidotomy in real life, it is more than likely that he/she will have had no formal training. Hence, we chose a group of experienced anaesthetists who had had no training in the sets assessed in order to mimic a real-life crisis.

A number of different cricothyroidotomy sets have been developed, often as prepackaged commercially available kits. This choice inevitably creates doubt as to which is the best to use in an emergency. We chose four of the currently available sets and selected sizes that gave the sets as similar characteristics as possible. We chose Melker's and Quiktrach sets with the same dimensions, with an internal diameter of 4 mm and length of 42 mm. The nearest comparable sizes for the Transtracheal Airway Catheter set and Patil's Airway were of smaller internal diameter. It has been shown that it is impossible to have a guaranteed successful exchange of gases through cannulae that have an internal diameter < 3 mm [5, 6]. This can be explained on the basis of Poiseuille's law, which states that flow is proportional to the fourth power of the internal radius. Our study obeys this law and confirms that ventilation and oxygenation with the larger Melker's and Quiktrach sets were more effective that with the other two sets. In addition to small diameter, difficult assembly of the equipment and a significant high overall failure rate rendered the Transtracheal Airway Catheter set and Patil's Airway unacceptable for clinical use.

Although it was quicker to insert the small diameter cannulae than the 4 mm cannulae, earlier and more reliable increases in PAo2 were achieved only with Quiktrach and Melker's sets. The use of a cannula with an internal diameter of 4 mm offers the advantage of ventilation with an anaesthetic circuit. Our study confirms the findings from a previous study that a standard reservoir bag can generate enough inspiratory pressure for an adequate tidal volume, while permitting exhalation in ≈ 4 s, resulting in a respiratory rate of 10–12 breath.min−1[7].

The successful use of a wire-guided technique for cricothyroidotomy, similar to Melker's set, has been reported in the literature [8]. Chan et al.'s study [9] claims that the use of Melker's set has advantages over surgical cricothyroidotomy. However, this study used formalin-preserved cadavers and parallels with the clinical situation may therefore be difficult to draw. In addition, no other cricothyroidotomy sets were compared with Melker's set. A study by Frei et al. [2] looked at the efficacy of the Quiktrach set in 55 cadavers. The conclusions of this study were that it was easy to use but had a high incidence of trauma to soft tissues and surrounding structures, as we have found in our study. These studies show that Melker's and Quiktrach sets are technically reliable. Our study confirms these results and reinforces their findings with simulated physiological data.

Our study has some drawbacks. The simulated cricothyroid membrane is inevitably not identical to a real membrane, and our subjects were not hampered in their efforts by haemorrhage or surgical emphysema. We re-used sets if they were not obviously damaged, which may have made subsequent attempts with a re-used set more difficult, and we did not assess whether the subjects' performance improved during the study. However, we believe that our results suggest that the Quiktrach set may be the best of the four studied in the clinical situation and that the Human Patient Simulator is a good training tool for emergency cricothyroidotomy.

Acknowledgements

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

We thank the Bristol Medical Simulation Centre and the Sir Humphry Davy Department of Anaesthetics at the Bristol Royal Infirmary, Cook UK Limited and VBM Limited for their help in completing this project. We thank Mr A Dhebri for his help in the statistical analysis.

References

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
  • 1
    Walls RM. Cricothyroidotomy. Emergency Medical Clinics of North America 1988; 6: 72536.
  • 2
    Frei FJ, Meier PYR, Lang FJW, Fasel JHD. Cricothyroidotomy with Quiktrach device. Anasthesie Intensivtherapie Notfallmedizin 1990; 25: 449.
  • 3
    Sanders J, Haas RE, Geisler M, Lupien AE. Using the Human Patient Simulator to trace the efficacy of an experimental emergency percutaneous trans-tracheal airway. Military Medicine 1998; 163: 54451.
  • 4
    Schillaci RF, Iacovoni VE, Conte RS. Transtracheal aspiration complicated by fatal endotracheal haemorrhage. New England Journal of Medicine 1976; 295: 48890.
  • 5
    Neff CC, Pfister RC, Sonnenberg EV. Percutaneous transtracheal ventilation: experimental and practical aspects. Journal of Trauma 1983; 23: 8490.
  • 6
    Dallen LT, Wine R, Benumof JL. Spontaneous ventilation via transtracheal large-bore intravenous catheter is possible. Anesthesiology 1991; 75: 5313.
  • 7
    Dworkin R, Benumof JL, Benumof R, Karagianes TG. The effective tracheal diameter that causes air trapping during jet ventilation. Journal of Cardiothoracic Anaesthesia 1990; 4: 7316.
  • 8
    Bainton CR. Cricothyrotomy. International Anesthesiology Clinics 1994; 32: 95108.
  • 9
    Chan TC, Vilke GM, Bramwell KJ, Davis DP, Hamilton RS Rosen P. Comparison of wire guided cricothyrotomy versus standard surgical cricothyrotomy technique. Journal of Emergency Medicine 1999; 17: 95762.