BJA Advance Access originally published online on June 1, 2006
British Journal of Anaesthesia 2006 97(2):255-261; doi:10.1093/bja/ael135
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First clinical experience of tracheal intubation with the SensaScope®, a novel steerable semirigid video stylet
1 Department of Anaesthesiology, University Hospital Zurich Switzerland
2 Department of Anaesthesiology, Gartnavel Hospital Glasgow, UK
3 Institute of Social and Preventive Medicine, University of Zurich Switzerland
*Corresponding author: Department of Anaesthesiology, University Hospital Zurich, Raemistrasse 100, CH-8091 Zurich, Switzerland. E-mail: peter.biro{at}usz.ch
Accepted for publication April 23, 2006.
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Abstract |
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Background. Problems with tracheal intubation are a major cause of anaesthesia-related morbidity and mortality. Difficulty with tracheal intubation is primarily a consequence of failure to see the vocal cords with conventional direct laryngoscopy. We report our experience with use of the SensaScope® for tracheal intubation in routine clinical practice.
Methods. The SensaScope® is a hybrid steerable semirigid S-shaped video stylet. Its handling and performance were assessed by anaesthetists with a minimum of 1 yr of experience. They performed four intubations each with the device in anaesthetized elective surgical patients. The view of the glottis with the Macintosh laryngoscope was compared with the view shown on the monitor by the SensaScope®. The time taken to complete intubation, the final tracheal tube (TT) position and the degree of difficulty of the procedure were recorded.
Results. Thirty-two patients were studied. All Macintosh Cormack and Lehane grade 3 patients were converted to grade 1 or 2 with the SensaScope®. Mean intubation time was 25 (12) s and correct mid-tracheal TT cuff position was achieved in all cases. The degree of difficulty was 3.0 (1.8) on a numerical scale ranging from 0 to 10. All operators rapidly became familiar with the device and mastered its technique of use.
Conclusion. The SensaScope® is a reliable and effective device for tracheal intubation under vision of the normal airway. It has great potential to facilitate management of difficult airway situations in anaesthetized and paralysed patients.
Keywords: airway, management; complications, difficult intubation; equipment, intubation stylet; intubation, fibreoptic; intubation, video assisted
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Introduction |
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TopAbstractIntroductionMaterial and methodsResultsDiscussionREFERENCES |
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Difficulty with airway management, particularly difficult tracheal intubation, is a major cause of anaesthesia-related morbidity and mortality. The safety of some aspects of airway management has improved in recent years. In particular, use of pulse oximetry and capnometry has reduced the frequency of undetected oesophageal intubation and non-specific respiratory complications. However, there has been little change in the incidence of complications caused by tracheal intubation.1 2 Although there are several definitions of difficult tracheal intubation, failure to achieve a view of the glottis (as defined by a grade 3 or grade 4 view according to the classification of Cormack and Lehane)3 is synonymous with difficult intubation in most patients.4 Although the tracheas of most patients may be intubated fairly readily with blind techniques, persistent attempts at intubation are associated with death or brain damage.5 We should aim to achieve intubation under direct vision of the glottis for all patients, but recent prospective studies show incidences of Grade 3 or 4 view with conventional laryngoscopy of 10 and 11%.6 7
Patients with predicted difficult tracheal intubation can be managed safely and reliably using a flexible fibrescope under topical anaesthesia (with careful sedation when it can be used safely). This approach is the gold standard of anticipated difficult airway management.8 9 However, unanticipated difficult intubation, which occurs after induction of anaesthesia and under complete neuromuscular block, involves immediate risks to the patient and no single technique has proved completely reliable. The most frequently used approach is blind probing for the glottic opening behind the epiglottis with a malleable stylet or an introducer.3 10–13 However, these blind techniques have a failure rate,14 may cause significant trauma,15 and whenever possible we should aim to intubate all our patients under vision.4 Other techniques which do not require direct laryngoscopy and are often successful include the Fasttrach® ILMA.16 However, it has a failure rate16 17 and can cause significant trauma.18
An alternative to blind techniques such as stylets and introducers is the use of devices which contain fibreoptic bundles because they provide a direct view of the airway from a viewpoint which is not available in standard direct laryngoscopy.19–21 The SensaScope® (Acutronic MS, CH-8816 Hirzel, Switzerland) is a new hybrid guidable semirigid video sytlet designed to facilitate intubation under vision. A unique feature is the S-shaped curve of the rigid part of the stylet. The technique of use is similar to a standard stylet, in that direct laryngoscopy is performed with the left hand and the stylet and tube are inserted with the right hand. The view from the tip of the device is displayed on a video screen. Thus, the user is guided by both the direct laryngoscopic view of the hypopharynx and the endoscopic image of the airway displayed on the video system.
No clinical data are yet available about the technique of use of the SensaScope® or its success rate in management of normal or difficult tracheal intubation. In this first clinical trial of the SensaScope®, its speed, efficacy, safety and simplicity of use in normal and difficult tracheal intubation were evaluated during routine anaesthesia.
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Material and methods |
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TopAbstractIntroductionMaterial and methodsResultsDiscussionREFERENCES |
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Study design
Prospective evaluation of technique, performance and success rate of the SensaScope® video stylet in patients undergoing general anaesthesia for elective surgery.
Description of the instrument
The SensaScope® is a 45 cm long light-weight video stylet with a rigid metal S-shaped shaft (Fig. 1). It has a 3 cm long steerable tip which can be flexed in the sagittal plane for 75° in both directions by operating a lever at the proximal end of the device. The proximal end also consists of an eyepiece [on which a charge coupled device (CCD) video camera can be mounted], a light source connector, and the proximal part of the shaft has a 15 mm female connector on which the tracheal tube (TT) is mounted securely. It is a hybrid device, having similarities and differences to flexible fibreoptic and rigid endoscopes. In contrast to most flexible fibreoptic scopes, this device has no working channel. The quality of the optics is comparable with that of flexible fibreoptic endoscopes.
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Intubation technique
The basic technique is similar to a stylet in that it is manoeuvred with the right hand, while the left hand performs conventional laryngoscopy with a Macintosh laryngoscope. The TT is fitted on to the SensaScope® and its rotation is adjusted so that the longest part of the distal bevel lies anteriorly. As a consequence of the smooth metallic surface of the shaft, it is not necessary to use a lubricant to ease railroading of the TT. The stylet tip should be wiped with a sterile anti-fog solution. A light source is then connected to the head of the device and a CCD-camera is mounted on the eyepiece (direct ocular viewing is possible but is not recommended). Because conventional Macintosh direct laryngoscopy is an inherent component of the technique, the SensaScope® must be operated with the right hand, the thumb operating the lever which adjusts the angle of the tip. Once the best view of the hypopharynx has been achieved with the Macintosh laryngoscope, the tip of the device is introduced gently into the oral cavity (Fig. 2). The scope should be kept as close as possible to the palate and as far as possible from the blade of the laryngoscope so that a ‘palatal’ rather than a ‘lingual’ route through the mouth is taken. This route facilitates an excellent view of the hypopharynx and the glottis. Once the tip of the scope has passed the incisor teeth, the user should watch only the video-monitor, on which the glottic opening and the whole intubation pathway can be seen as the device is advanced into the trachea (Fig. 3). Once the tip has passed the vocal cords, the Macintosh laryngoscope is removed, and the SensaScope® is further advanced until the tip lies at the level of mid-trachea. This is achieved by simultaneously lowering the scope in the sagittal plane and guiding the tip by adjusting its distal flexible segment as it is advanced. The anatomical S-shape of the rigid shaft has been designed to facilitate smooth and atraumatic insertion deep into the trachea. When the tracheal carina appears on the screen, the SensaScope® is held firmly in position and the TT is railroaded carefully into the trachea with the left hand until it is seen on the screen (Fig. 4). The TT position is now adjusted under direct visual control. Finally, the SensaScope® is removed while holding the TT firmly in place with the left hand.
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2 cm above the carina. The tube is held firmly in this position. 14. Right hand: the thumb is removed from the control lever so that the tip of the scope returns to neutral position. The SensaScope® is withdrawn carefully.Measurements and clinical evaluation
The investigation was approved by the local Ethics Committee and oral informed consent was obtained from patients. Eight anaesthetists (operators) with a professional experience of at least 1 yr were invited to use the SensaScope® for regular tracheal intubation, which was planned during elective gynaecological and urological surgery in our university hospital. After a brief demonstration of the intubation technique with the device in a standardized step-by-step fashion on an intubation manikin (Laerdal, N-4002, Stavanger, Norway), the operators performed orotracheal intubation with the device in anaesthetized patients, while supervised by one of the investigators. The investigator did not interfere with performance of the procedure, but occasionally gave advice and reminders. The time from inserting the laryngoscope until completion of the intubation was defined as the ‘intubation time’. The operator was asked to record the best possible direct laryngoscopy view using the classification of Cormack and Lehane (CL grade)3 and an assessment of the degree of difficulty of the whole intubation process, using a numeric scale ranging from 0 (very easy) to 10 (extremely difficult). Each operator was asked to use the device in four different patients. These sequential data were used to assess the learning curve for this technique. The views of the glottis achieved with the direct laryngoscope were compared with the views from the SensaScope®. Intubation time and estimated degree of difficulty when performing the intubation procedure were correlated with the duration of professional experience (months of work in anaesthesia) and experience with flexible fibreoptic intubation, comparing a lower level of experience (fewer than 20 fibreoptic intubations), with a higher level of experience (20 or more fibreoptic intubations).
Continuous and ordinal data are presented as mean (SD) or median (range) when appropriate. To address this correlation, intubation time and degree of difficulty for each operator were analysed using an ANOVA for repeated measurements within factor operator and time-dependent covariate (laryngoscopic CL grade) or between factor (professional experience), respectively. Post hoc tests were performed using Bonferroni-test. CL grades are presented as number and percentage of patients. CL grades achieved with direct laryngoscopy were compared with those acquired with the SensaScope® by applying the sign test to mean CL grades for each operator. P-values <0.05 are considered statistically significant.
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Results |
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Thirty-two intubations were performed with the SensaScope® by eight operators. The patients were 29 females and 3 males with the following biometric data: age 45 (21–74) yr, height 166 (8) cm and weight 72 (16) kg. The eight operators had a median professional experience of 28 months ranging from 12 to 264 months. Four of them were skilled with fibreoptic intubation (having performed
20 cases), and the other four had less experience (having performed <20 cases). All intubations were successful. The duration of the whole procedure never exceeded 1 minute and no significant decrease in SpO2 occurred in any patient. In all cases, the final position of the TT cuff in mid-trachea was confirmed on the video screen. The CL grade view of the larynx achieved with direct laryngoscopy was 1 in 6 patients (19%), 2 in 19 patients (59%) and 3 in 7 patients (22%). The CL grade view achieved with the SensaScope® improved to 1 in 30 patients (94%) and from 3 to 2 in the remaining 2 patients (6%) (P=0.008). The mean intubation time was 25 (12) s, and the overall level of difficulty for the entire procedure was estimated by the operators as 3.0 (1.8) (median 3, range 0–7). Increased CL grade during conventional direct laryngoscopy was associated with a slight increase in the time taken to perform the intubation with the SensaScope® and also resulted in a statistically significant increase in the estimated level of difficulty (Table 1). However, even in laryngoscopic CL grade 3 patients, the estimated degree of difficulty was only 4.3 (1.9), which implies reasonable ease of use.
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There was no significant relationship between the duration of professional experience and intubation performance reflected in duration of intubation and the final TT position with the SensaScope®. However, the degree of expertise with conventional flexible fibreoptic intubation correlated inversely with the intubation time (Table 2). The intubation time decreased during the four consecutive patients for each operator, decreasing by half during the second intubation (Fig. 5). There were no complaints of sore throat or injury related to the intubation process by any patients.
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0.005 after Bonferroni correction). |
Discussion |
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TopAbstractIntroductionMaterial and methodsResultsDiscussionREFERENCES |
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This study set out to investigate the first clinical experience with the SensaScope®, a new semirigid steerable video stylet. Selection of operators who had at least 1 yr of professional experience was based on the assumption that sufficient knowledge and expertise in conventional laryngoscopy is a prerequisite to mastering this technique. Use of the SensaScope® after a single training session with step-by-step instruction showed a steep learning curve, in that after two intubations a high success rate was achieved and the average duration of intubation was only 20 s (Fig. 5). All subsequent uses were performed smoothly and handling rapidly became intuitive. The anatomical shape of the SensaScope® has facilitated tracheal intubation under vision without force or trauma in all patients studied so far, but it is possible that modification of the shape will be required in the light of further experience.
The 32 cases investigated occurred during regular clinical work and contained a mix of patients with different degrees of visibility of the glottis during conventional direct laryngoscopy. Increase in CL grade was associated with longer SensaScope® intubation time, but this difference was not statistically significant. Although the estimated degree of difficulty with the SensaScope® increased with higher direct laryngoscopy CL grades, it remained low, even in CL grade 3 (Table 1). This finding suggests that the device may facilitate rapid tracheal intubation under vision of patients with difficult airways. The view of the glottis obtained with the SensaScope® was grade 1 in 30 patients and grade 2 in 2 patients, both of whom were CL grade 3 with conventional laryngoscopy. Conversion of 7 CL grade 3 patients to 1 or 2 is very important in clinical practice as it permits tracheal intubation to be performed under vision in these patients.4
Subjective rating of the level of difficulty in handling the instrument revealed a very low overall value. This is probably a consequence of the fact that the initial part of the intubation procedure uses conventional direct laryngoscopy and the subsequent technique involves simple guidance under visual control. On the other hand, operators who have expertise with flexible fibreoptic laryngoscopy perform better as a consequence of familiarity with the technique of steering the tip of the scope (Table 2). However, advancement of the scope into the airway is facilitated by the rigid shaft of the device, in comparison with a completely flexible device. Many problems encountered with flexible fibreoptic intubations are a consequence of difficulty in rotating the advancing scope because its shaft is so floppy that it does not completely transmit axial movement to the tip. Furthermore, the floppiness of the shaft contributes to difficulty in railroading the TT. These problems are avoided with the SensaScope®, which gives the operator more control of the instrument than can be achieved with a floppy device. Thus, the combination of a rigid shaft with a steerable tip provides the advantages of both systems while avoiding the problems inherent in handling a completely flexible system.10 22 23
A limitation of this study is that the incidence of CL grade 3 during direct laryngoscopy in our patients was higher than in most studies. The incidence of CL grades 3 and 4 depends on many factors such as age, state of dentition and laryngoscopy technique. We did not use external laryngeal manipulation (ELM) while performing direct laryngoscopy in order to make the technique comparable with the SensaScope® technique. In prospective studies in which ELM was not used, the incidence of grade 3 or 4 CL view was 10%7 and 11%.6 The remainder of the different incidence in our results may be a consequence of the fact that the operators exerted only a limited lifting force with the Macintosh laryngoscope. The importance of lifting force and ‘forceful elevation of the epiglottis’ during direct laryngoscopy has been stressed by others.24 We believe that omission of ELM and limitation of elevating force during direct laryngoscopy has produced the higher incidence of CL grade 3 view in our patients. The need to apply less forceful elevation of the laryngoscope might be considered a beneficial effect of the SensaScope® technique.
We did not undertake a power analysis as we had no means of predicting the difference in the incidence of CL grade 3 views. We believe this is not necessary in a preliminary report.
The intubation technique of the SensaScope® is an extension of conventional laryngoscopy. It offers an improved view of the glottis, simultaneous direct and endoscopic views, full visual control over the passage of the TT and confirmation of its final intratracheal position. When unanticipated difficult intubation occurs after induction of anaesthesia, the device can be assembled rapidly and used almost immediately.
Use of the SensaScope® has other advantages. There is no need for extreme head-extension or forced traction of the laryngoscope which may cause dental injury or adverse cardiovascular responses. This technique does not require additional personnel. The SensaScope® can be used to monitor routine tracheal intubation and to improve the success rate of unanticipated difficult tracheal intubation. The monitor view can facilitate recognition of unanticipated subglottic airway pathology so that airway management can be optimized.25 The view from the tip of the SensaScope® facilitates adjustment of the TT position so that the tip is above the tracheal carina and the cuff is in a mid-tracheal position.
An additional benefit of the use of the video-monitor is that all personnel can watch the endoscopic view and help to facilitate the intubation (e.g. taking over the laryngoscope and optimizing ELM, if necessary).21 26 Although the device can be used without the video-monitor by looking directly into the eyepiece, this direct ocular technique would require more extensive movements by the user to follow the instrument and offers a less good overview of the actual position of the scope. Furthermore, this direct ocular technique was not assessed in this investigation and cannot be recommended.
As a consequence of the limited available experience with the SensaScope®, its feasibility for intubation of awake patients under topical anaesthesia is not yet known. In the present version preparation of the scope consists of mounting the TT, applying an anti-fog solution to the scope tip, and attaching the light cable and the CCD-camera. Light intensity, white balance, focus and rotational alignment of the camera are then adjusted. Preparation requires up to 3 min. However, future development of an inbuilt light source and camera will shorten preparation time and simplify handling.
Maintenance of the SensaScope® is much easier than of flexible fibrescopes.27 28 The SensaScope® is not autoclavable. Therefore it requires chemical disinfection, and it is fully immersible in disinfectant solution. As a consequence of its smooth metal surface, it is easy to clean by immersion in a suitable detergent fluid (e.g. 1% Sekusept® aktiv, Ecolab GmbH, Düsseldorf, Germany) for 60 min. Absence of a working channel eliminates some concerns about cleaning and sterilization.
This combination of properties suggests that the SensaScope® technique is easy to learn and that it has great potential to make airway management more precise and safer than is the case with direct laryngoscopy alone. Further experience in patients with unanticipated difficult intubation is needed before the full extent of the potential of the SensaScope® can be established.
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Acknowledgments |
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P. Biro designed the SensaScope® and is involved in development of the device in cooperation with Acutronic MS, CH-8816 Hirzel, Switzerland, the manufacturer of the prototypes. This investigation has been carried out under the patronage of the New European Surgical Academy (NESA), Karower Strasse 11/214, D-13125 Berlin, Germany.
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