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New options for airway management: intubating fibreoptic stylets †

2003; Elsevier BV; Volume: 91; Issue: 3 Linguagem: Inglês

10.1093/bja/aeg011

1471-6771

Edwin B. Liem, David G. Bjoraker, Dietrich Gravenstein,

Tracheal and airway disorders

Fibreoptic and video technologies are widely used for airway management. Fibreoptics have been used in most airway intubation devices, including rigid laryngoscopes and in the tracheal tube wall itself.10Frass M Kofler J Thalhammer F et al.Clinical evaluation of a new visualized endotracheal tube.Anesthesiology. 1997; 87: 1262-1263Crossref PubMed Scopus (13) Google Scholar 22Pollack CP, Bradley BB, Jordon RC, Mackin RA, Marrriot W. Fiberoptic-enhanced endotracheal tube for bedside teaching of intubation skills. Annual meeting of the Society for Academic Emergency Medicine, Washington DC, May 1997Google Scholar Optical stylets, which incorporate flexible fibreoptic imaging elements in an intubation stylet, have now also become available. More than 10 new optical stylet devices have been introduced since 1995, which shows that combining viewing capability with the familiar handling of a stylet is an appealing concept (Table 1). But are these useful tools? Are their clinical performances similar or is one best? We survey the evolution of optical stylets, describe their properties, summarize their clinical performance and describe an ideal system.Table 1History of optical stylets. *Alternative designs without stylet functionality but with similar viewing capabilitiesManufacturerDeviceYear introduced/commercially available (✓)American OpticalFiberoptic Laryngoscope1974American Optical (for Karl Storz KG)Optical stylet1979American OpticalFiberoptic Stylet Laryngoscope1983Karl Storz KG (Germany)Bonfils Retromolar Intubation Fiberscope1983 (✓)Anesthesia Medical Specialties (AMS)Fiberlightview Shuttle1994 (✓)Clarus Medical LLC (Ventus brand name)Shikani Seeing Stylet1996 (✓)Nanoptics, Inc.Nanoscope1997Scientific Sales InternationalFlexguide1997Volpi AG (Switzerland)Video-Optical modified Schroeder Stylet1997Pulmonx, Inc.Visualized Endotracheal Tube (VETT)*1997 (✓)Imagyn Medical Technologies Inc.Aeroview1998Volpi AG (Switzerland)Video-Optical Intubation Stylet (VOIS)1998Jedmed Instrument Co. (US distributor for Machida Corp. Japan)Machida Portable Stylet Fiberscope (PSS-6)1999Nihon Koden (Japan)StyletScope1999 (✓ Japan only)Acutronic Medical Systems AG (Baar, Switzerland – similar to device by Volpi AG)Video-Optical Intubation Stylet (VOIS)2000 (✓ Europe only)Parker MedicalTrachView Videoscope*2000 (✓) Open table in a new tab Almost 35 years ago, Murphy reported successful nasal intubation using a flexible choledochoscope placed through a tracheal tube.19Murphy P A fibre-optic endoscope used for nasal intubation.Anaesthesia. 1967; 22: 489-491Crossref PubMed Scopus (107) Google Scholar Flexible fibreoptic technology was then used to assist with intubation. The Flexible Fiberoptic Laryngoscope was a short flexible bronchoscope with a pistol-grip handle, angulation control lever and eyepiece (Fig. 1). The use of this device was reported in 197232Stiles CM Stiles QR Denson JS A flexible fiber optic laryngoscope.JAMA. 1972; 11 (1246–7): 221Google Scholar and additional reports soon followed.3Applebaum EL Laryngeal and tracheal problems in patients with central nervous system and spinal disorders.Otolaryngol Clin North Am. 1979; 12: 829-835PubMed Google Scholar 9Ford RW Adaptation of the fiberoptic laryngoscope for tracheal intubation with small diameter tubes.Can Anaesth Soc J. 1981; 28: 479-480Crossref PubMed Scopus (10) Google Scholar 23Raj PP Forestner J Watson TD Morris RE Jenkins MT Techniques for fiberoptic laryngoscopy in anesthesia.Anesth Analg. 1974; 53: 708-714Crossref PubMed Scopus (33) Google Scholar 33Wang JF Reves JG Corssen G Use of the fiberoptic laryngoscope for difficult tracheal intubation.Ala J Med Sci. 1976; 13: 247-251PubMed Google Scholar 40Witton TH An introduction to the fiberoptic laryngoscope.Can Anaesth Soc J. 1981; 28: 475Crossref PubMed Scopus (14) Google Scholar Over the years other similar devices were developed—the Port-O-Scope (Mercury Medical, Clearwater, FL, USA) and the Rapiscope (Cook Critical Care, Bloomington, IN, USA)—but unlike the flexible bronchoscope, they never found widespread use.8Chiu JW Goh MH Ip-Yam PC Fibre-optic aided bougie (FAB) for simulated difficult tracheal intubation.Ann Acad Med Singapore. 2000; 29: 47-49PubMed Google Scholar 28Selwyn D Spiers P A new indication for the Cook critical care Rapiscope.Anaesthesia. 1996; 51: 1076Crossref PubMed Scopus (4) Google Scholar Katz and Berci4Berci G Katz R Optical stylet: an aid to intubation and teaching.Ann Otol Rhinol Laryngol. 1979; 88: 828-831Crossref PubMed Scopus (10) Google Scholar 13Katz RL Berci G The optical stylet – a new intubation technique for adults and children with specific reference to teaching.Anesthesiology. 1979; 51: 251-254Crossref PubMed Scopus (9) Google Scholar coined the term 'optical stylet' in 1979 to describe a straight rigid endoscope used as a tracheal tube stylet during intubation (Fig. 2). Although used extensively for teaching purposes, its rigid straight design limited its use in difficult airway management. Bonfils modified this by adding a fixed curve to the distal end (Fig. 3). The Bonfils Retromolar Intubation Fiberscope (Karl-Storz, Culver City, CA, USA) was used for difficult intubations from a retromolar approach.7Bonfils P Schwierige Intubation bei Pierre-Robin-Kindern, eine neue Methode: der retromolar Weg.Anaesthesist. 1983; 32: 363-367PubMed Google ScholarFig 3Modification of the Katz and Berci's 'optical stylet' (Fig. 2) by addition of a fixed curve to its distal end.View Large Image Figure ViewerDownload (PPT) The earliest intubation aid with fibreoptic technology in a semi-malleable and formable stylet was the Fiberoptic Stylet Laryngoscope, introduced in the mid-1970s (Fig. 4). 20Patil VU Fiberoptic endoscopy in Anesthesia. Yearbook Medical Publishers (now Mosby), Chicago1983: 9-15Google Scholar This configuration remains popular. Despite their popularity, the first optical stylets developed are no longer commercially available. More recent devices with a Schroeder stylet design18Moncure K Cypel D Cantillo J Goldberg ME Preliminary evaluation of the Aeroview scope system (AVSS).Anesthesiology. 1998; 3A: SEE46Google Scholar 36Weiss M Management of difficult tracheal intubation with a video-optically modified Schroeder intubation stylet.Anesth Analg. 1997; 85: 1181-1182Crossref PubMed Google Scholar (Aeroview, Imagyn, Newport Beach, CA, USA; Video-optical Schroeder Stylet, Volpi AG, Schlieren, Switzerland; Flexguide, Scientific Sales International Inc., Kalamazoo, MI, USA) have also met with commercial failure. The Schroeder stylet does not hold a specific shape but can be flexed anteriorly by depressing a lever on the proximal end of the device (Fig. 5). The position of the lever means that these devices must be held at their proximal end like a dagger. The Aeroview is the only Schroeder-stylet-based system that has been studied clinically (Fig. 6). In a small study using the Aeroview, only seven of 13 patients with uncomplicated airways were intubated successfully, despite jaw thrust, sniffing position and tongue retraction.18Moncure K Cypel D Cantillo J Goldberg ME Preliminary evaluation of the Aeroview scope system (AVSS).Anesthesiology. 1998; 3A: SEE46Google Scholar Ease of use was 2.8 (sd 0.8) on a scale of 1–5 (poor–superior). The investigators concluded that experience was needed to use the device successfully and this may have contributed to its commercial failure. The characteristics of all commercially available fibreoptic stylet devices are summarized in Table 2.Table 2Technical specifications of commercial devices (alphabetical order). *Length of the device part on which the tracheal tube is mounted.DeviceStylet diameter × lengthFibre typePixel countAngle of viewViewing elementLight sourceFlexibility and radius of curvatureBonfils Fiberscope5 mm × 40 cmGlass12 00090°EyepieceStorz fiberoptic connectorRigid with 45° anterior tip curvatureFiberlightview Shuttle3.5 mm × 33.5 cm (0 channels)Glass10 00070°EyepieceBattery handleStylet malleable to 90° (deflectable tip optional)Machida Portable Stylet Fiberscope5.4 mm × 39.5 cmGlassNA80°EyepieceBattery-powered light sourceMalleable to 90°Shikani Seeing Stylet5mm × 27 cmGlass30 00070°EyepieceFiberoptic connector, laryngoscope handle or battery handleMalleable to 90°StyletScope7.0 mm ETPlastic350050°EyepieceLight source handle and battery boxDeflectable tip with 75° anterior flexionTrachview Videoscope5.5 mm ETGlass10 000100°CCDCustomUsed with stylet or external ET guideVideo-Optical Intubation Stylet (Acutronic)3.8 mm × 40 cmGlass10 00050°CCDCustomMalleable to 90°Visualized EndoTracheal Tube10.4 mm (OD) 7.0 or 8.0 mm (ID)Glass600070°CCDCustomFlexible—use with any styletET=endotracheal tube; CCD=charge-coupled device; OD=outer diameter; ID=internal diameter; NA=not available Open table in a new tab ET=endotracheal tube; CCD=charge-coupled device; OD=outer diameter; ID=internal diameter; NA=not available Two devices, the Visualized Endotracheal Tube (VETT, Pulmonx, Inc., Palo Alto, CA, USA) and TrachView (Parker Medical, Englewood, CO, USA), are not optical stylets because the optics are not incorporated into a shape-retaining stylet (Figs 7 and 8). However, the VETT, with optical fibres embedded in its wall, forms an image from the tip of the tube and can be manipulated using a standard stylet. The TrachView intubation system is a flexible fibreoptic viewing element designed to be placed either alongside a stylet within a tracheal tube or inside a tracheal tube when an external intubation guide is used to hold the shape of a tracheal tube (Fig. 9). The TrachView system resembles the method described by Lupien and colleagues17Lupien AE Taylor C Hybrid intubation technique for the management of a difficult airway: a case report.AANA J. 1995; 63: 50-52PubMed Google Scholar using a flexible fibreoptic endoscope alongside a conventional intubation stylet in the tracheal lumen.Fig 8The TrachView.View Large Image Figure ViewerDownload (PPT)Fig 9The Trach view external endotracheal tube guide.View Large Image Figure ViewerDownload (PPT) The stylet diameter determines the minimum size of tracheal tube that can be used. Paediatric versions exist of the Fiberlightview Shuttle (Anesthesia Medical Specialties, Santa Fe Springs, CA, USA), the Shikani Seeing Stylet (Clarus Medical, Minneapolis, MN, USA) and the Video-Optical Intubation Stylet38Weiss M The pediatric video-optical intubation stylet.Internet J Anesthesiol. 1998; 2N4http://www.ispub.com/journals/IJA/Vol2N4/vois.htmGoogle Scholar (VOIS; Volpi AG, Schlieren, Switzerland). Most optical stylets use glass fibres to transmit the image to an eyepiece or camera. However, the Nanoscope (Nanoptics, Gainesville, FL, USA)11Gravenstein D Lampotang S Melker R Doviak R Performance of a plastic optical fiber stylet for tracheal intubation of a dog.J Clin Monit Comput. 1998; 14: 271-274Crossref PubMed Scopus (3) Google Scholar 12Gravenstein D Melker RJ Lampotang S Clinical assessment of a plastic optical fiber stylet for human tracheal intubation.Anesthesiology. 1999; 91: 648-653Crossref PubMed Scopus (21) Google Scholar (Fig. 10) and the StyletScope (Nihon Koden Corp., Tokyo, Japan)15Kitamura T Yamada Y An efficient technique for tracheal intubation using the StyletScope alone.Anesthesiology. 2000; 92: 1210-1211Crossref PubMed Scopus (75) Google Scholar 16Kitamura T Yamada Y Du HL Hanaoka K Efficiency of a new fiberoptic Styletscope in tracheal intubation.Anesthesiology. 1999; 91: 1628-1632Crossref PubMed Scopus (45) Google Scholar (Fig. 11), have image guides made of plastic. Plastic fibreoptic fibres are quite resistant to breakage compared with glass, but often have a lower pixel count, which reduces image resolution. The image brightness also decreases more rapidly in plastic fibres as the image guide length increases, because plastic fibres absorb more light than do glass fibres. More recently, plastic optical fibres with 7000 or more pixels and high clarity have begun to rival their glass counterparts. A comparative clinical trial of a 3000-pixel Nanoscope graded the view as 8 on a 1–10 scale, compared with 10 by direct laryngoscopy and flexible fibreoptic endoscopy.12Gravenstein D Melker RJ Lampotang S Clinical assessment of a plastic optical fiber stylet for human tracheal intubation.Anesthesiology. 1999; 91: 648-653Crossref PubMed Scopus (21) Google Scholar The poorer image quality did not affect the success rate for intubation in this comparative study. The image quality of the StyletScope with 3500-pixel resolution appeared to be inferior compared with glass fibrescopes, which typically use 10 000 or more pixels.16Kitamura T Yamada Y Du HL Hanaoka K Efficiency of a new fiberoptic Styletscope in tracheal intubation.Anesthesiology. 1999; 91: 1628-1632Crossref PubMed Scopus (45) Google Scholar However, the 3500-pixel resolution of the StyletScope was clear enough for successful intubation. The minimum number of pixels needed for a clinically useful image is not known. Both pixel count and display size affect image quality. Low-pixel-count devices tend to use eyepieces or smaller display screens (15 cm diagonal or less) because they pack pixels more tightly and give the illusion of a sharper image.Fig 11The StyletScope.View Large Image Figure ViewerDownload (PPT) Objects are focused by a distal objective lens in the tip of the optical stylet. The lens has an angle of view, which is the cone-shaped visual field. Greater angles provide a more panoramic view. Fibreoptic stylets have angles of view ranging from 50° to 100°. Wide-angled views can help to find the glottic opening when the stylet tip is not in the midline or encounters an anterior or deviated glottis. The distal lenses in all the fibreoptic stylets have a focal length of 5–50 mm, which is adequate for intubation purposes. Stylet channels allow oxygen insufflation, drug administration, and suctioning. Few optical stylets have channels (Aeroview, Bonfils fiberscope, Fiberlightview Shuttle (Fig. 12), Optical Stylet) because they increase stylet diameter and limit the size of the tracheal tube that can be mounted. In reusable systems, these channels can transmit infection if they are not properly cleaned.24Reeves DS Brown NM Mycobacterial contamination of fibreoptic bronchoscopes.J Hosp Infect. 1995; 30: 531-536Abstract Full Text PDF PubMed Scopus (31) Google Scholar The Shikani Seeing Stylet (Fig. 13) lacks an oxygen insufflation channel but allows for insufflation through the tracheal tube itself. The VETT has a large unobstructed channel for selective suction under indirect vision because the optical fibres are in the tracheal tube wall.Fig 13The Shikani Seeing Stylet with stylet bending tool shown below.View Large Image Figure ViewerDownload (PPT) Most fibreoptic stylets have a proximal focusing lens in a standard 32-mm outside-diameter eyepiece. A camera can be attached to the eyepiece, in the same way as with flexible fibreoptic endoscopes, for viewing on a monitor. However, adding hardware to the proximal end of the tracheal tube can increase the stylet weight, which makes the optical stylet difficult to manoeuvre with one hand. With a camera attached to an eyepiece, the monitor display size should be considered. Larger displays (38 cm diagonal) can be used for devices with 10 000 or more pixels. If a larger display is used with devices with fewer pixels, the image shows the cladding around the individual optical fibres, producing a honeycomb-patterned image that can be difficult to interpret. In contrast, the Nanoscope, TrachView Videoscope (Parker Medical, Englewood, CO, USA), VOIS (Fig. 14) and VETT do not use a traditional monocular eyepiece with a proximal lens. Instead, they use a long image guide that connects to a charge-coupled device, which transmits the image directly to a monitor. This avoids adding weight to the stylet–tracheal tube assembly, but needs special connectors, a custom light source and a monitor. An integral camera could provide a better image than a traditional eyepiece, with automatic focus, automatic zoom and image enhancement filter. However, these features may not always produce a better image. Excessive light may saturate a charge-coupled device, turning the displayed image into a blank screen. The video system of the Aeroview did not reliably adapt to increased light intensities and we experienced numerous 'whiteouts' during intubation. Many fibreoptic stylets have a battery-powered light source. This is convenient because the user is no longer tethered to the fibreoptic light source. However, a lithium battery can increase cost if batteries have to be replaced frequently. If a stylet cannot be bent forwards, it may not be useful if neck extension or mouth opening is limited, or if the larynx is anterior. The Bonfils Retromolar Fiberscope is a rigid scope but has a 45° curvature built into its distal end. The newest Styletscope is rigid proximally but the tip has a 90° anterior flexibility.14Kimura A Yamakage M Chen X Kamada Y Namiki A Use of the fibreoptic stylet scope (Styletscope™) reduces the hemodynamic response to intubation in normotensive and hypertensive patients.Can J Anaesth. 2001; 48: 919-923Crossref PubMed Scopus (19) Google Scholar The remaining fibreoptic stylets have varying degrees of malleability with an anterior curvature of at least 90°. The first detailed case report was of the Fiberoptic Stylet Laryngoscope for intubation in a patient with a difficult airway caused by an anterior mediastinal mass and superior vena cava syndrome.29Shapiro HM Sanford TJ Schaldach AL Fiberoptic stylet laryngoscope and sitting position for tracheal intubation in acute superior vena cava syndrome.Anesth Analg. 1984; 63: 161Crossref PubMed Scopus (10) Google Scholar Having a hand free to position the head and palpate and manipulate the larynx was noted to be an advantage. An optical stylet can be used in stand-by mode for rescue when conventional direct laryngoscopy fails, as shown with the VOIS. 34Weiss M Goldmann K Schwarz U Video-assisted tracheal intubation through the Fastrach-LMA using a video-optical intubation stylet.Internet J Anesthesiol. 1999; 3N2http://www.ispub.com/journals/IJA/Vol3N2/ilma.htmGoogle Scholar 39Weiss M Video-intuboscopy: A new aid to routine and difficult tracheal intubation.Br J Anaesth. 1998; 80: 525-527Crossref PubMed Scopus (36) Google Scholar Two patients with unexpected Cormack grade III views were successfully intubated using the VOIS to display the vocal cords on a video screen. The head, neck and larynx did not need manipulation, nor was help needed from an assistant. Gravenstein and colleagues reported a similar experience with a Nanoscope prototype.12Gravenstein D Melker RJ Lampotang S Clinical assessment of a plastic optical fiber stylet for human tracheal intubation.Anesthesiology. 1999; 91: 648-653Crossref PubMed Scopus (21) Google Scholar Two abstracts describe the intubation of 35 emergency patients with a VETT.21Pollack CP, Bradley BB, Jordon RC, Mackin RA. ED clinical trial of a fiberoptic-enhanced endotracheal tube for intubation, monitoring, tube placement, confirmation and difficult airway management. Annual meeting of the Society for Academic Emergency Medicine, Washington DC, May 1997Google Scholar 22Pollack CP, Bradley BB, Jordon RC, Mackin RA, Marrriot W. Fiberoptic-enhanced endotracheal tube for bedside teaching of intubation skills. Annual meeting of the Society for Academic Emergency Medicine, Washington DC, May 1997Google Scholar Eleven of the airways were 'difficult' because of anatomy, blood or secretions but all were intubated successfully. The VETT aided success in eight of these intubations. The Bonfils Retromolar Intubation Fiberscope was used in a clinical trial of 103 patients with unexpected difficult airways.25Rudolph C Schlender M Clinical experiences with fiberoptic intubation with the Bonfils intubation fiberscope.Anaesthesiol Reanim. 1996; 21: 127-130PubMed Google Scholar Initial airway evaluation was made under general anaesthesia. Most of the patients in this trial (80%) were undergoing ENT or oro-maxillo-facial surgery and 17% had Cormack grade III and IV airways. All the patients were intubated successfully by the mouth (not retromolar) using the Bonfils Retromolar Intubation Fiberscope. The optical stylet was the sole intubation device in 80% of patients. However, a Macintosh blade was still used in conjunction with the Bonfils Fiberscope in the remaining 20% of patients. No patient with limited mouth opening or severely limited neck extension was intubated during this study. Presumably the fixed anterior curvature of the device would make it difficult to negotiate the oro-tracheal angle in these patients, and the authors themselves remarked that the device was probably not suitable for such patients. The Machida Fiberscope (Fig. 15) was used with patients with Cormack grade III and IV (16 of 34 patients) on conventional direct laryngoscopy.27Saruki N Saito S Sato J Kon N Tozawa R Swift conversion from laryngoscopic to fiberoptic intubation with a new, handy fiberoptic stylet.Anesth Analg. 1999; 89: 526-528PubMed Google Scholar The optical stylet was inserted beyond the tongue along the blade of the laryngoscope. Visualization and intubation was successful in all patients, but it was not clear if the Machida Fiberscope could be used as a sole intubation device. This is the only study that reports the duration of intubation. The 28–30 s duration of intubation was not significantly greater than in patients with Cormack grade I, II or IIIa airways (where 'a' denotes that the epiglottis does not touch the posterior pharynx). Duration of intubation was longer in some patients with Cormack grade IIIb and IVa airways ('b' indicates that the epiglottis is in contact with the posterior pharynx), taking up to 64 s. The jaw-thrust manoeuvre might move the epiglottis away from the posterior pharyngeal wall and is better than conventional direct laryngoscopy.2Aoyama K Takenaka I Nagaoka E Kadoya T Jaw thrust maneuver for endotracheal intubation using a fiberoptic stylet.Anesth Analg. 2000; 90: 1455-1459Crossref Scopus (24) Google Scholar The Shikani Seeing Stylet was evaluated in both adults and children.30Shikani AH New "seeing" stylet-scope and method for the management of the difficult airway.Otolaryngol Head Neck Surg. 1999; 120: 113-116Crossref PubMed Scopus (53) Google Scholar A small number (4%) of patients were intubated awake. In anaesthetized patients, intubation was with the patient in the sniffing position with manual jaw elevation. The Cormack grade was not measured by direct laryngoscopy, but according to the first view obtained through the optical stylet; 6% of the patients had Cormack grade III or IV airways. Cricoid pressure was needed in 17.5% of patients to see the glottis, and a Macintosh laryngoscope was needed in 8% of patients to retract the tongue. The Macintosh blade combined with the Shikani Seeing Stylet was better than either the blade or the stylet alone. The success rate was 88% after one intubation attempt, 97% after two and 100% after three attempts. In all of these clinical trials, the sniffing position was used when possible and conventional laryngoscopy was often used as well. Success rates might be different if these devices were the sole intubation device in patients with limited neck extension, limited mouth opening or recognized difficult airway. The Nanoscope study was the only clinical trial in which a prospective randomized comparison was made between optical stylet intubation, conventional direct laryngoscopy and flexible fibreoptic endoscopy.12Gravenstein D Melker RJ Lampotang S Clinical assessment of a plastic optical fiber stylet for human tracheal intubation.Anesthesiology. 1999; 91: 648-653Crossref PubMed Scopus (21) Google Scholar The Nanoscope was used as a sole device, without conventional direct laryngoscopy. Patients with known or suspected difficult airways (Mallampati class IV26Samsoon GLT Young RB Difficult tracheal intubation: a retrospective study.Anaesthesia. 1987; 42: 487-490Crossref PubMed Scopus (1118) Google Scholar) were excluded from the study, but a difficult airway was partially simulated by intubating patients while keeping the head position neutral. Novice users obtained a success rate of 96%, with one failure due to bleeding. This compared well with flexible fibreoptic endoscope intubations. Intubation time was longer than direct laryngoscopy but shorter than with flexible fibreoptic bronchoscopy. In the StyletScope clinical trial, head positions were also deliberately kept neutral to simulate a difficult airway.16Kitamura T Yamada Y Du HL Hanaoka K Efficiency of a new fiberoptic Styletscope in tracheal intubation.Anesthesiology. 1999; 91: 1628-1632Crossref PubMed Scopus (45) Google Scholar The device was used in conjunction with a Macintosh blade, which was used to help elevate the tongue. The successful intubation rate was 94% after one attempt and 100% after two attempts. The pre-operative Mallampati classification was not related to the time for intubation (29 (sd 14) s). Similar results were obtained in a study when patients were intubated in the sniffing position with no attempt to simulate a difficult airway.15Kitamura T Yamada Y An efficient technique for tracheal intubation using the StyletScope alone.Anesthesiology. 2000; 92: 1210-1211Crossref PubMed Scopus (75) Google Scholar Weiss and colleagues37Weiss M Schwarz U Gerber A Difficult airway management: comparison of the Bullard laryngoscope with the video-optical intubation stylet.Can J Anaesth. 2000; 47: 280-284Crossref PubMed Scopus (38) Google Scholar used a manikin with a simulated difficult airway by limiting head extension to give a Cormack grade III view. Forty anaesthesia personnel compared, in randomized order, the Bullard laryngoscope and VOIS. Mean intubation times were similar – about 19 s – but the VOIS was associated with fewer failed intubations (8/400 vs 41/400). The VOIS was also compared with a conventional malleable stylet in this way.6Biro P Weiss M Gerber A Pasch T Comparison of a new video-optical intubation stylet versus the conventional malleable stylet in simulated difficult tracheal intubation.Anaesthesia. 2000; 55: 886-889Crossref PubMed Scopus (21) Google Scholar While the VOIS needed 20.4 (7.7) s for intubation, 10 s longer than with a conventional stylet, it avoided oesophageal and endobronchial intubations (both 39.2% of times with the conventional stylet). Another manikin-based difficult-airway study of the VOIS had no failures, and a mean intubation time of 17.4 (6.8) s.5Biro P Weiss M Comparison of two video-assisted techniques for the difficult intubation.Acta Anaesthesiol Scand. 2001; 45: 761-765Crossref PubMed Scopus (13) Google Scholar Extensive learning for optical stylets was not noted in studies, 31Smith JE Jackson APF Hurdley J Clifton PJM Learning curves for fibreoptic nasotracheal intubation when using the endoscopic video camera.Anaesthesia. 1997; 52: 101-106Crossref PubMed Scopus (69) Google Scholar except for the Aeroview system. For the Shikani Stylet, a brief initial learning period was noted for a single operator.30Shikani AH New "seeing" stylet-scope and method for the management of the difficult airway.Otolaryngol Head Neck Surg. 1999; 120: 113-116Crossref PubMed Scopus (53) Google Scholar An intubation success rate of 96% was achieved in another study of a device used by 16 novice operators,12Gravenstein D Melker RJ Lampotang S Clinical assessment of a plastic optical fiber stylet for human tracheal intubation.Anesthesiology. 1999; 91: 648-653Crossref PubMed Scopus (21) Google Scholar but these intubations were done under the guidance of more experienced users. For the Stylet Scope trial, no preliminary training specific to the technique was made and no significant difference was found between intubation times for the first five patients (33 (8) s) compared with the last five patients (29 (14) s) on a total of 32 intubations.16Kitamura T Yamada Y Du HL Hanaoka K Efficiency of a new fiberoptic Styletscope in tracheal intubation.Anesthesiology. 1999; 91: 1628-1632Crossref PubMed Scopus (45) Google Scholar The lack of significant further decrease in intubation time after 27 uses suggests that operation of the device was easy to learn. With a simulated difficult airway in manikins, the number of failed attempts using a Bullard laryngoscope decreased from the first five intubation attempts (30/200 failures/attempts) to the last five (11/200).37Weiss M Schwarz U Gerber A Difficult airway management: comparison of the Bullard laryngoscope with the video-optical intubation stylet.Can J Anaesth. 2000; 47: 280-284Crossref PubMed Scopus (38) Google Scholar For the VOIS in the same study, failed attempts were few and did not decrease from attempts 1–5 to attempts 6–10 (6/200 and 2/200, respectively). However, the mean intubation time improved by 6 s (27%).37Weiss M Schwarz U Gerber A Difficult airway management: comparison of the Bullard laryngoscope with the video-optical intubation stylet.Can J Anaesth. 2000; 47: 280-284Crossref PubMed Scopus (38) Google Scholar The fewer failures and shorter intubation times suggest that the VOIS was easier to use. Simulating a Cormack grade III laryngeal view in 50 paediatric patients, a 92% successful intubation rate within 40 s was obtained with the VOIS.35Weiss M Hartmann K Fischer J Gerber AC Video-intuboscopic assistance is a useful aid to tracheal intubaton in pediatric patients.Can J Anaesth. 2001; 48: 691-696Crossref PubMed Scopus (27) Google Scholar Intubation time improved by the fifth patient (20.8 (10.9) s) compared with the first (24.5 (17.3) s) but this difference was not significant. When four operators with over 3 years experience used the Shikani Seeing Stylet as a sole intubation device,1Agro F Cataldo R Carassiti M Costa F The Seeing Stylet: a new device for tracheal intubation.Resuscitation. 2000; 44: 177-180Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar the intubation success rates were lower than in the original trial by Shikani, which suggests that training is needed. Generally, learning with the optical stylets seems rapid, but most studies were by the original inventors or by people working under their guidance. Failure to intubate had several causes, but was rarely because of device malfunction. The Bonfils Fiberscope trial had a 3.7% failure in the initial part of the study, caused by a problem with the fixation of the tracheal tube onto the stylet. This problem was quickly solved. A study that tested for failure using a prototype plastic optical fibre system reported a partial distal lens separation after 40 bend-and-straighten cycles.11Gravenstein D Lampotang S Melker R Doviak R Performance of a plastic optical fiber stylet for tracheal intubation of a dog.J Clin Monit Comput. 1998; 14: 271-274Crossref PubMed Scopus (3) Google Scholar No other study found technical difficulties with the optical stylet devices. Secretions can obscure the lens, which with the Shikani Seeing Stylet caused a 20% failure rate on first attempt.1Agro F Cataldo R Carassiti M Costa F The Seeing Stylet: a new device for tracheal intubation.Resuscitation. 2000; 44: 177-180Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar Kitamura and colleagues15Kitamura T Yamada Y An efficient technique for tracheal intubation using the StyletScope alone.Anesthesiology. 2000; 92: 1210-1211Crossref PubMed Scopus (75) Google Scholar 16Kitamura T Yamada Y Du HL Hanaoka K Efficiency of a new fiberoptic Styletscope in tracheal intubation.Anesthesiology. 1999; 91: 1628-1632Crossref PubMed Scopus (45) Google Scholar reported two failures resulting from mucus on the lens, requiring additional attempts. The Nanoscope study had a failed intubation caused by blood on the recessed lens.12Gravenstein D Melker RJ Lampotang S Clinical assessment of a plastic optical fiber stylet for human tracheal intubation.Anesthesiology. 1999; 91: 648-653Crossref PubMed Scopus (21) Google Scholar Secretions caused complications with the Shikani Seeing Stylet, and successful intubation required a change from the original stylet curvature to a hockey-stick shape in 10% of patients.1Agro F Cataldo R Carassiti M Costa F The Seeing Stylet: a new device for tracheal intubation.Resuscitation. 2000; 44: 177-180Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar The curve of the stylet required adjustment in one patient in the Machida Fiberscope trial.27Saruki N Saito S Sato J Kon N Tozawa R Swift conversion from laryngoscopic to fiberoptic intubation with a new, handy fiberoptic stylet.Anesth Analg. 1999; 89: 526-528PubMed Google Scholar This shows that perhaps up to 100° of anterior flexion may be needed for successful intubation in some patients. Not all fibreoptic stylets provide this amount of flexion. In the Nanoscope trial, one patient was described where no view was obtained.12Gravenstein D Melker RJ Lampotang S Clinical assessment of a plastic optical fiber stylet for human tracheal intubation.Anesthesiology. 1999; 91: 648-653Crossref PubMed Scopus (21) Google Scholar Conventional direct laryngoscopy with a Miller 3 blade found a true difficult airway with Cormack grade IV view. The optical stylet was then passed under the retracted epiglottis to show the vocal cords and the patient was intubated successfully. The StyletScope trial reported minor sore throat in 28% patients and minor hoarseness in 25% on the first post-operative day.16Kitamura T Yamada Y Du HL Hanaoka K Efficiency of a new fiberoptic Styletscope in tracheal intubation.Anesthesiology. 1999; 91: 1628-1632Crossref PubMed Scopus (45) Google Scholar The optical stylet in the Nanoscope trial caused less sore throat (median 1.0 on a scale of 0–10, with 10 being the worst) than direct laryngoscopy (median 3.0) but not statistically less than with fibreoptic bronchoscopy (median 2.0).12Gravenstein D Melker RJ Lampotang S Clinical assessment of a plastic optical fiber stylet for human tracheal intubation.Anesthesiology. 1999; 91: 648-653Crossref PubMed Scopus (21) Google Scholar Avoiding direct laryngoscopy may limit pharyngeal trauma and reduce the severity of postoperative sore throat. The ideal optical stylet provides an image of high clarity, which requires more than 10 000 pixels. The stylet must provide illumination. Orientation and steering are best with a lens of long focal length (50 mm) and large angle of view (≥90°). The ideal optical stylet system will be available in paediatric and adult sizes. Compared with a conventional stylet, the optical stylet will provide features such as imaging, illumination, an accessible channel, malleability and additional tip flexion without altering the weight, diameter, balance or handling. It produces an image that can be viewed from an eyepiece or displayed on a monitor. Re-usable systems will be robust and tolerate multiple bend-and-straighten cycles. Temperatures in excess of 60°C, needed for re-sterilization, will not affect components. Cost varies, and is not considered here because no cost-per-use analysis of an optical stylet has been reported. All systems except the VETT are reusable, but no information about the average number of uses before mechanical failure or maintenance and repair costs is available for any device. A review of the reports of clinical experience with the intubating fibreoptic stylet scopes suggests they are useful devices whose operation is easy to learn. It seems likely they will find an expanding role in the management of the airway. The features of different stylets reflect different preferences and practices among clinicians. We found that the most important features are image quality and familiar handling. Availability of an extra channel or tip flexion were less important. The device whose use and feel is most like a conventional stylet, gives a view from the tip of the tracheal tube, and can be bent to view around an obstruction will need least time and effort to learn. The VOIS is the only commercially available device that has good optics and can be used very much like a conventional stylet. The Stylet Scope is an alternative but has a lower resolution image. Unfortunately, because experience of re-use of these systems has not been described, we cannot offer an opinion on the value of these devices in comparison with other methods.