Observations on the assessment and optimal use of videolaryngoscopes.
The PubMed database was used to identify relevant videolaryngoscopy papers from 1990 to 2010. The key words for the literature search were videolaryngoscopy and videolaryngoscope. All publications in English were used to provide a list of videolaryngoscopes. Any videolaryngoscopes not available in Australia at the beginning of 2010 were excluded (e.g. McGrath[R] Mac, Aircraft Medical, Edinburgh, UK). The seven most commonly studied types of videolaryngoscopes were selected for appraisal from the generated list. Australian manufacturers or local distributors were contacted to provide their device for trial over a period of at least four weeks. Devices were trialled in normal airways and potential difficult airways (e.g. manual inline neck stabilisation, trauma, retrognathia and patients who had undergone previous radiotherapy for laryngeal carcinoma) by the authors in a number of centres.
The first author (KBG) was responsible for summarising the feedback from the other authors as experts in videolaryngoscopy. No formal data collection to document difficulties was instituted at this initial phase and, therefore, there were no numerators or denominators for specific device problems encountered.
The videolaryngoscopes assessed were:
* C-Mac videolaryngoscope[TM]--Macintosh No. 2, 3 and 4 blades, Miller No. 0, 1, 3 and 'Dorges' or D-blade (Karl Storz, Tuttlingen, Germany),
* Venner AP Advance video laryngoscope[TM]-Macintosh No. 3 and 4 blade and Difficult Airway Blade (DAB)--(Venner Medical, Switzerland),
* C-Trach[TM] (The Laryngeal Mask Company Ltd, Maidenhead, UK),
* Glidescope videolaryngoscope[TM], Glidescope Cobalt videolaryngoscope[TM] and Glidescope Ranger videolaryngoscope[TM] (Verathon Medical Inc., Bothell, WA, USA),
* Pentax-AWS system[TM] ("AirwayScope") (Pentax Corp., Tokyo, Japan),
* Airtraq[TM] (Prodol, Vizcaya, Spain), and
* McGrath Series 5 laryngoscope[TM] (Aircraft Medical, Edinburgh, UK).
The results of the assessments are summarised in Table 1.
TECHNIQUE TO ACHIEVE LARYNGOSCOPY
C-Mac videolaryngoscope and Venner AP Advance video laryngoscope Macintosh 3 and 4 blades sit along the floor of the mouth and displace the submandibular tissues antero-laterally. All other VL devices are passed over the dorsum of the tongue and require little or no elevation of the submandibular tissues for successful laryngoscopy.
Failed laryngoscopy often occurred with the CTrach and Venner AP Advance videolaryngoscope--DAB in patients with severe retrognathia where the curvature of the device did not correspond to the dorsum of the tongue. The Glidescope videolaryngoscope and the McGrath Series 5 laryngoscope have a lower profile, which made it easier to manipulate in this group of patients. However, the 60-degree angulation of the Glidescope videolaryngoscope made insertion of the blade around the tongue difficult in patients with severe retrognathia, short necks, obesity and barrel-shaped chests. This problem was overcome when the upper cervical spine could be extended. The ability to detach the blade from the McGrath Series 5 laryngoscope also overcame this problem in several patients.
It was noted that the Venner AP Advance videolaryngoscope with Macintosh 3 and 4 blades was the same shape as the C-Mac videolaryngoscope with the camera in the same position on the blade. For a limited number of patients the laryngoscopy view on the screen was worse than the C-Mac videolaryngoscope. The authors postulate that the direction of the camera on the C-Mac videolaryngoscope must differ from the Venner AP Advance videolaryngoscope Macintosh 3 and 4 blades.
ADJUNCT REQUIRED FOR SUCCESSFUL TRACHEAL INTUBATION
When considering tracheal intubation, the devices were classified into those which had an inbuilt conduit for the tracheal tube and those that required either a stylet or bougie.
a) In-built conduits (Airtraq, Pentax-AWS system, C-Trach and the Venner AP Advance videolaryngoscope--Difficult Airway Blade)
This group has a 'fixed' curvature. Successful laryngoscopy and intubation occurred when the device's curvature matched a normal or nearnormal oral cavity. The effect of the in-built conduit differed between the Airtraq and the Pentax-AWS system, both within their conduits and beyond in the supraglottic region.
The Pentax-AWS system has a narrower tracheal tube conduit. The tube travels for a short distance almost in line with the blade tip before angling upwards. We found the tip of the Pentax-AWS system needed to be under the epiglottis and close to the glottis for successful intubation. A small number of failures were reported with Pentax-AWS system in patients with long necks where the tip of the blade could not reach the epiglottis. In these cases the tracheal tube tip impacted in the vallecula.
The Airtraq has a wide integrated conduit and the tip of a Magill-shaped tube initially dropped as it exits. It then moved anteriorly following the airway configuration. We found that if the Airtraq was too close to the glottis, the tube tip entered the oesophagus (Figure 1).
Two solutions were helpful in these cases. Either the device was partially removed to allow more room for the tracheal tube to curve upwards to the airway configuration or a bougie was inserted down the tube. The latter elevated the tracheal tip into the larynx. Silicone-based tracheal tubes (e.g. Fastrach) are not pre-shaped and thus failed to negotiate the up-sloping vestibule axis to reach the glottis.
The C-Trach epiglottic elevator bar pushed the epiglottis upwards. This allowed the soft tip of the Fastrach tube to pass through the glottis and along the anterior wall of the trachea.
b) Stylet/bougie required for tracheal intubation (C-Mac videolaryngoscope, Venner AP Advance videolaryngoscope--Macintosh 3 and 4 blades, Glidescope videolaryngoscope and McGrath Series 5 laryngoscope)
These videolaryngoscopes routinely required either a stylet or bougie for tracheal intubation. The devices that flattened the submandibular tissues (e.g. C-Mac videolaryngoscope and Venner AP Advance video laryngoscope--Macintosh 3 and 4 blades) favoured the use of a straight bougie with a short coude tip to manoeuvre through an upward sloping laryngeal vestibule.
[FIGURE 1 OMITTED]
The other devices in this group conformed to the dorsum of the tongue without flattening of the submandibular space (i.e. Glidescope videolaryngoscope and McGrath Series 5 laryngoscope). These devices required a J-shaped styleted tube to manoeuvre around the tongue and enter the glottis. A problem occurred when advancing a polyvinyl chloride tube off the stylet and through the glottis. The tip of the polyvinyl chloride (PVC) tubes often impacted on the anterior wall of the subglottic space.
DEVICE POSITION FOR LARYNGOSCOPY
Laryngoscopy devices are designed for insertion into the upper airway to provide a glottic image by one of two methods: either in the midline over the tongue; or along the floor of mouth with displacement of tongue and flattening of the submandibular space.
These two methods of laryngoscopy are rarely interchangeable between laryngscopes. A device that functions in the floor of the mouth displacing the tongue and compressing the submandibular tissues should not be used over the tongue nor should a device that is designed to pass over the tongue be used along the floor of the mouth. Correct positioning is critical for successful function of these devices during laryngoscopy and intubation. Frequently, operators inexperienced with devices designed for insertion over the tongue attempt to place them along the floor of the mouth. Though this may occasionally provide a view of the larynx, tracheal intubation is often difficult, as the position of the misplaced device now does not match that of the specifically shaped rigid stylet.
MANIPULATION OF THE TRACHEAL TUBE FOR INTUBATION
The ultimate goal of videolaryngoscopy is successful tracheal intubation. Videolaryngoscopes may either have an integrated tracheal tube conduit or require a stylet or bougie for tracheal intubation. The shape of these conduits and stylets should match that of the patient's airway passage. It may be difficult to replicate this shape in such cases as micrognathia or acromegaly with macroglossia (17) to the fixed curvature of a device with an in-built conduit. In these cases a bougie (18,19) or fibreoptic bronchoscope (20) may be necessary to negotiate the airway. In contrast a stylet may have the advantage of being more adjustable (21).
When using a Glidescope videolaryngoscope, the problem of advancing the PVC tube off the stylet with impaction of the tip on the anterior wall of the subglottic space (22) can be solved by the use of a Parker Flex-Tip tracheal tube or a silicone tube (such as the Fastrach tracheal tube). The Parker Flex-Tip tracheal tube has a posterior facing bevel and a curved tip that will slide over the anterior tracheal wall rather than impact on it. Similarly, a silicone tube tip is more pliable than PVC and likely to slide down the trachea. The stylet should not be removed completely from the silicone tube after the tip has passed the glottis as it will tend to buckle in the pharynx. We recommend the stylet be removed from a Fastrach tube in 1 to 2 cm increments as the tube in advanced. After ensuring 4 to 5 cm of the tube is in the trachea, the stylet is removed completely.
Duff and co-workers (23) showed that the Eschmann and Frova bougies had only success rates of 65 and 75% respectively with the Glidescope videolaryngoscope while the 60-degree curved stylet was 100% successful.
Bougies with a short coude tip may be used successfully with the Glidescope videolaryngoscope by any of five mechanisms. The blade may displace a relatively small tongue. Second, the operator uses more force to displace the tongue and submandibular tissues. Both of these techniques create a short laryngeal vestibule and make the use of a bougie more favourable. Third, a curved Magill tracheal tube with a shape similar to the oral cavity may be used as a conduit for the bougie (24) or the shape of the bougie is changed to replicate the shape of the videolaryngoscope blade. Finally, the operator may use a retromolar approach for inserting the bougie therefore bypassing the tongue as with the other group of VL. None of these manoeuvres are universally helpful. Their different roles should be carefully considered during airway training.
The shape of the McGrath Series 5 laryngoscope and the recommended shaping of the bougie and tracheal tube closely resemble those of the Glidescope videolaryngoscope13 with all the same concerns.
The C-Mac videolaryngoscope elevates the mandible and displaces the submandibular tissues antero-laterally. As a result the laryngeal vestibule is relatively short. A short coude tip bougie (25) may be required as an aid for tracheal intubation. The handling of the C-Mac videolaryngoscope during laryngoscopy and intubation is similar to that of the conventional Macintosh blade (26) and should be intuitive to most anaesthetists (27).
A recent study by Cavus (28) of the C-Mac videolaryngoscope D-blade has shown that it can improve Cormack and Lehane laryngoscopy grades from 3 or 4 to 1 or 2a. A 'semiflexible tube guide' was required as part of the intubation technique. This work demonstrated a rapid intubation rate though these results need to be repeated in different clinical scenarios.
VIDEOLARYNGOSCOPY FOR THE OCCASIONAL OPERATOR
Videolaryngoscopy is not currently part of any difficult airway algorithm (29-32). This is likely to change in the future (33); for now it is reasonable to include it as a rescue manoeuvre during difficult intubation when patient oxygenation is well maintained. Given their high success rate at tracheal intubation in failed Macintosh intubations, the videolaryngoscope may well become the alternate blade of choice over others, such as the Miller and McCoy (34-36).
The operator should gain enough exposure and training with the device they plan to use to ensure competence. The extent of this training will probably vary from device to device. Training in laryngoscopy usually starts with the Macintosh blade. This blade is inserted along the floor of the mouth and displaces the tongue and submandibular tissues laterally and anteriorly. It is therefore natural to expect an anaesthetist with only occasional exposure to difficult airways to adopt a videolaryngoscope that replicates this familiar action as this will have a shorter learning curve than some of the other devices.
The C-Mac videolaryngoscope design is based on the Macintosh blade. Several studies have shown that anaesthetists find this device easy to use with a high successful tracheal intubation rate, with or without the use of a gum elastic bougie (3,16,25,37-41). It is possible that the Venner AP Advance video laryngoscope Macintosh No. 3 and 4 blades may produce similar results but there is currently insufficient research with this device.
One common difficult airway scenario is the patient with a normal airway requiring manual in-line neck stabilisation for instability of the cervical spine following trauma or with cervical spine pathology. The occasional operator who has little experience with the Macintosh blade will find the Airtraq and the Pentax-AWS system user-friendly. Their inflexible nature, however, may make it difficult to manage a distorted airway as in severe retrognathia.
Our assessment of videolaryngoscopes fits a previously published airway concept, the Two-Curve theory (42). This theory considers the airway passage as two curves, the primary curve (or oro-pharyngeal airway) and the secondary curve (or pharyngo-glotto-tracheal airway). It also describes how these curves change in different head and neck positions. We feel that such a theory may provide insight into future assessments of these devices.
We have examined the function of commonly used videolaryngoscopes based on the technique used to achieve successful laryngoscopy and the adjunct used for tracheal intubation. Some devices follow the dorsum of the tongue while others flatten the submandibular space. The method of laryngoscopy has a direct effect on the appropriateness of the choice of device for successful tracheal intubation.
This approach to videolaryngoscopes considers the effect of airway configuration rather than relying solely on what a specific device may offer the operator. It may provide the foundation for future structured approaches that are based on airway configurations in normal and difficult airway scenarios.
A feature common to all videolaryngoscopes is that the point of view of the glottis is moved to a point within the oropharynx and aimed along the laryngeal vestibule axis to the glottis. They are classified according to both the position of the device in the airway to achieve its line of sight during laryngoscopy and the method required for tracheal intubation.
The authors would like to thank Dr Phil Allen for his assistance with the preparation of the article.
CONFLICT OF INTEREST DECLARATION
The authors have received the devices reviewed in this article free of charge for assessment from the following companies: Prodol, Vizcaya, Spain (Airtraq [TM]); Pentax Corp., Tokyo, Japan (Pentax-AWS System [TM]); the Laryngeal Mask Company Ltd, Maidenhead, UK (C-Trach [TM]); Venner Medical, Switzerland (Venner AP Advance video laryngoscope [TM]--DAB, Macintosh 3 and 4 blade); Verathon Medical Inc., Bothell, WA, USA (Glidescope videolaryngoscope [TM]); Aircraft Medical, Edinburgh, UK (McGrath Series 5 laryngoscope [TM]); Karl Storz, Tuttlingen, Germany (C-Mac videolaryngoscope [TM]).
Drs K. B. Greenland and M. J. Edwards have not received any financial incentives from any of the companies mentioned in this paper. All devices were provided free of charge to these doctors for a limited time and then returned to the company.
Dr R. Segal has conducted workshops using all the videolaryngoscopes mentioned in this paper. This equipment was provided free of charge for use in these workshops. Dr Segal has also received funding from Karl Storz to attend the 2011 European Society of Anaesthesiology meeting in Helsinki.
Dr C. Acott has received equipment from Karl Storz, LMA PacMed, Coveidin, Abbott Medical Pty. Ltd. and Cook Medical Pty. Ltd. for AusAid work in Papua New Guinea and Fiji.
Dr W. H. L. Teoh has conducted and instructed at airway workshops in the Asia-Pacific region, using the videolaryngoscopes in this paper which were provided free of charge for use in these workshops. Dr Teoh received funding from Karl Storz to attend the 2011 Airway Management Special Interest Group meeting in Coolum, Queensland.
Dr W. P. L. Bradley has not received any financial support from any manufacturers. These companies do supply videolaryngoscopes free of charge on a loan basis for his airway workshops.
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K. B. GREENLAND *, R. SEGAL ([dagger]), C. ACOTT ([double dagger]), M. J. EDWARDS ([section]), W. H. L. TEOH **, W. P. L. BRADLEY ([dagger][dagger])
Department of Anaesthesia and Perioperative Medicine, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia; Department of Anaesthesia and Pain Management, Royal Melbourne Hospital and Department of Anaesthesia and Perioperative Medicine, The Alfred, Melbourne, Victoria, Australia; Department of Anaesthesia, Royal Adelaide Hospital, Adelaide, South Australia, Australia and Department of Women's Anaesthesia, KK Women's and Children's Hospital, Singapore
* MB, BS, MD, FANZCA FHKAM, Consultant Anaesthetist, Wesley Anaesthesia and Pain Management, Wesley Medical Centre; Honorary Associate Professor, Department of Anaesthesiology, University of Hong Kong, Queen Mary Hospital, Hong Kong SAR; and Senior Lecturer, Burns, Trauma and Critical Care Research Centre, School of Medicine, University of Queensland.
([dagger]) MB, ChB, FANZCA, NBETEeXAM, Staff Specialist, Department of Anaesthesia and Pain Management, Royal Melbourne Hospital.
[double dagger] MB, BS, FANZCA, Staff Anaesthetist, Department of Anaesthesia, Royal Adelaide Hospital.
([section]) BS, MB, BS, FANZCA, PG Dip Echo, Staff Specialist, Department of Anaesthesia and Perioperative Medicine, Royal Brisbane and Women's Hospital.
** MB, BS, FANZCA, Consultant Anaesthetist, Department of Women's Anaesthesia, KK Women's and Children's Hospital; Adjunct Assistant Professor, Duke-NUS Graduate Medical School; and Clinical Lecturer, Yong Loo Lin School of Medicine, National University of Singapore.
([dagger] [dagger]) MB, ChB, FANZCA, Specialist Anaesthetist, Department of Anaesthesia and Perioperative Medicine, The Alfred; and Adjunct Lecturer, Academic Board of Anaesthesia and Perioperative Medicine, Monash University.
Address for correspondence: Dr K. B. Greenland, Wesley Anaesthesia and Pain Management, Suite 17, Level 2, Wesley Medical Centre, 40 Chasely Street, Auchenflower, Qld 4066.
Table 1 Characteristics of videolaryngoscopes and recommendations for optimum use Airway device Technique to achieve Adjunct required (Manufacturer, laryngoscopy for successful City, Country) tracheal intubation * C-Mac videolaryngoscope[TM] (Karl Storz, Tuttlingen, Germany) Macintosh No.2, 3 and Blade of device Stylet/bougie with 4 blades and V-MAC placed on floor of coude tip Storz Berci DCI mouth; operator uses the device to lift the mandible and submandibular tissues Miller No. 0, 1 Blade of device Stylet/bougie with/ placed on floor of without coude tip mouth; operator uses the device to lift the mandible and submandibular tissues 'Dorges' or D-blade Blade of device J-shaped Stylet placed in midline over dorsum of tongue or on floor of mouth; the operator does not use the device to lift the mandible or submandibular tissues Venner AP Advance videolaryngoscope[TM] (Venner Medical, Switzerland) Macintosh No. 3 and 4 Blade of device Stylet/bougie with blade placed on floor of coude tip mouth; operator uses the device to lift the mandible and submandibular tissues Difficult Airway Blade of device Conduit Blade or DAB placed in midline over dorsum of tongue; the operator does not use the device to lift the mandible or submandibular tissues C-Trach[TM] (The Device placed in Conduit Laryngeal Mask Company midline over dorsum Ltd, Maidenhead, UK) of tongue; the operator does not use the device to lift the mandible or submandibular tissues. Glidescope Blade of device J-shaped Stylet videolaryngoscope[TM], placed in midline Glidescope Cobalt over dorsum of videolaryngoscope[TM] tongue; the operator and Glidescope Ranger does not use the videolaryngoscope[TM] device to lift the (Verathon Medical mandible or Inc., Bothell, WA, submandibular USA) tissues. Pentax-AWS system[TM] Blade of device Conduit ("AirwayScope") placed in midline (Pentax Corp., Tokyo, over dorsum of tongue Japan) A with the tip lifting the epiglottis; the operator does not use the device to lift the mandible or submandibular tissues. Airtraq[TM] (Prodol, Blade of device Conduit Vizcaya, Spain) placed in midline over dorsum of tongue; the operator does not use the device to lift the mandible or submandibular tissues McGrath Series 5 Blade of device J-shaped Stylet laryngoscope[TM] placed in midline (Aircraft Medical, over dorsum of Edinburgh, UK) tongue; the operator does not use the device to lift the mandible or submandibular tissues Airway device Recommended tracheal Recommendations for (Manufacturer, tube optimum use City, Country) C-Mac videolaryngoscope[TM] (Karl Storz, Tuttlingen, Germany) Macintosh No.2, 3 and Magill-shaped C-Mac Macintosh, V-MAC 4 blades and V-MAC polyvinyl chloride and Miller blades are Storz Berci DCI tube used in manner similar to the traditional laryngoscope blade counterparts on which they are modeled. They are placed on the floor of mouth and elevate the mandible and submandibular tissues. A standard bougie with small coude tip (or similarly shaped stylet) is appropriate adjuncts in many difficult airways where lift of the epiglottis is incomplete. Miller No. 0, 1 Magill-shaped polyvinyl chloride tube 'Dorges' or D-blade Parker Flex-Tip[TM] The Magill-shaped tube tracheal tube is often appropriate but changes in its curvature may be required using a stylet to match the patient's oro- pharyngeal curvature. A Parker Flex-Tip[TM] tracheal tube avoids the problem of the standard bevelled tip which will impact on the anterior wall of the subglottic space. Venner AP Advance videolaryngoscope[TM] (Venner Medical, Switzerland) Macintosh No. 3 and 4 Magill-shaped The AP Advance blade polyvinyl chloride Macintosh blades tube should function in a manner similar to the standard Macintosh blade. However, more work needs to be performed before the authors can recommend further guidelines. Difficult Airway Magill-shaped The Difficult Airway Blade or DAB polyvinyl chloride Blade has a high tube profile and therefore is difficult to insert in patients with limited mouth opening or severe retrognathia (where the blade needs to be inserted cephalically and requires extra mouth opening). C-Trach[TM] (The Fastrach[TM] The camera frequently Laryngeal Mask Company tracheal tube fogs and should be Ltd, Maidenhead, UK) warmed before insertion. Fastrach[TM] tracheal tubes do not have intubation marks to indicate depth of insertion. The operator should be aware of the possibility that endobronchial intubation may occur. Glidescope Parker Flex-Tip[TM] The blade should be videolaryngoscope[TM], tracheal tube kept in the midline Glidescope Cobalt over the dorsum of the videolaryngoscope[TM] tongue. and Glidescope Ranger videolaryngoscope[TM] A J-shaped tracheal (Verathon Medical tube-stylet is the Inc., Bothell, WA, best shape with the USA) curvature starting approximately 9 cm proximal to the tube cuff in adults. The sniffing position is the best position to avoid tracheal tip impacting on the anterior subglottic space. Parker Flex-Tip[TM] tracheal tube with posterior facing bevel is ideal tube because the curved tip slides along the anterior tracheal wall without the frequent problems of impaction that occurs with standard beveled tubes. Pentax-AWS system[TM] Magill-shaped High success rate but ("AirwayScope") polyvinyl chloride may fail in patients (Pentax Corp., Tokyo, tube with long necks. In Japan) A these cases the device tip fails to reach and elevate the epiglottis leading to failed intubation. Insertion of a bougie down the conduit has been reported to be successful in these situations. Airtraq[TM] (Prodol, Magill-shaped Suitable for use in Vizcaya, Spain) polyvinyl chloride many circumstances tube including paediatric patients. The device should be kept well above the glottis so that the Magill-shaped tube will curve upwards into it after it exits the in-built conduit. If the tube repeatedly enters the cricopharyngeus, the device should be partially withdrawn. McGrath Series 5 Parker Flex-Tip[TM] Functions like laryngoscope[TM] tracheal tube Glidescope (Aircraft Medical, videolaryngoscope[TM] Edinburgh, UK) with recommended J-shaped stylet and Parker Flex-Tip[TM] tracheal tube. Detachment of blade for insertion in patients with short neck and barrel chest may be advantageous. Position of the videolaryngoscopy blade within upper airway to achieve successful laryngoscopy: midline over dorsum of tongue (i.e. over tongue largely conforming to the oropharyngealspace); floor of mouth (i.e. along floor of mouth with lateral displacement of tongue). Adjunct required for successful tracheal intubation: conduit-integrated tracheal tube conduit with device's blade; stylet/bougie with coude tip-standard straight stylet/bougie with short coude; J-shaped stylet-stylet inside tracheal tube with distal curve approximating blade of device with distal curvature starting 9 cm proximal to tube tip. Note: Parker Flexi-tip tracheal tube (Parker Medical, Highlands Ranch, CO, USA).
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|Title Annotation:||Point of View|
|Author:||Greenland, K.B.; Segal, R.; Acott, C.; Edwards, M.J.; Teoh, W.H.L.; Bradley, W.P.L.|
|Publication:||Anaesthesia and Intensive Care|
|Date:||Jul 1, 2012|
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