The present and future of fiberoptic intubation

Difficult airway management is critical during induction of anesthesia, and airway-related complications are the most frequent causes of morbidity, mortality and litigation against anesthesiologists . Fiberoptic intubation (FOI) is the gold standard for endotracheal intubation in difficult or compromised airway situations when preservation of spontaneous breathing is detrimental 4, . However, FOI is still not a routine technique due to lack of education and practice . In this paper we presented basic principles of fiberoptic intubation, together with the recent developments in this field.


Introduction
Difficult airway management is critical during induction of anesthesia, and airway-related complications are the most frequent causes of morbidity, mortality and litigation against anesthesiologists [1][2][3] .Fiberoptic intubation (FOI) is the gold standard for endotracheal intubation in difficult or compromised airway situations when preservation of spontaneous breathing is detrimental 4,5 .
However, FOI is still not a routine technique due to lack of education and practice 6 .In this paper we presented basic principles of fiberoptic intubation, together with the recent developments in this field.

Fiberoptic bronchoscope
Although numerous types of supraglottic devices, rigid fiberoptic scopes and video-laryngoscopes were developed in recent years, fiberoptic bronchoscope is the only available device for nasal intubation, and is the recommended device for tracheal intubation under topical anesthesia in awake patients.
A part of light waves is transmitted, absorbed or reflected.The light is reflected along glass fibers and leaves them on the other end.A group of optic fibers forms a bundle.A typical bundle consists of 10,000 fibers, each of them has an 8 to 10 m diameter.In order to minimize light deflection, each fiber is surrounded with 1 m of isolator.Picture transmitting fibers known as coherent bundle consist of specifically arranged fibers.
A fiberoptic bronchoscope (FOB) consists of the body, an endoscope, universal light transmitter, camera and monitor or eye-piece (Figure 1).The FOB body has a handle for moving the end of the endoscope in the vertical (up and down) plain, an eye-piece with a knob or button for adjusting the focus of the image, and a working channel that can be used for aspiration of secretions or delivery of oxygen or drugs.The endoscope, which is protected with waterproof plastic, contains optic fibers which transmit images from the end of the scope to the eye-piece or LCD screen, and also contains a non-coherent bundle for transmitting light from the light source to the object of interest.
FOBs designed for tracheal intubation newer, in addition to the work channel for aspiration of secretions, an incorporated antifogging system.The latest FOB model (Olympus MAF type include TM Olympus Medical Systems Corporation, Tokyo, Japan) has an incorporated camera, light source, small monitor and recording system (Figure 2).This type of FOB enables FOI in emergency cases and on the field, lowers the cost of equipment and is suitable for education.Tele-anesthesia is a recent, interesting development, whereby developments in robotic surgery are applied in anesthesia.As a result, a successful nasal and oral FOI has been performed on an airway simulation mannequin, using the multipurpose DaVinci Surgical System type S (DVS), (Intuitive Surgical, Sunnyvale, California, USA) 7 .

Basic principles of FOI
The first case of FOI was described in 1973 8 .Today FOI is considered a basic anesthesia skill and new generations of anesthesiologists are expected to learn the techniques of nasal and oral FOI 6,9,10 .Education on FOI is a complex process, because data show that courses and practice on mannequins are not as effective as expected.In addition, real-life problems like secretions and airway dynamics cannot be effectively simulated, but can be seen on previously made recordings.The new FOI education system is based on American Heart Association echosonographic teaching known as "practice while watching" [9][10][11] .
FOI is indicated when airway management with direct laryngoscopy is expected to be difficult or impossible (Table 1).Contraindications to FOI are relative and are related to the skills of the anesthesiologist (Table 2).Skills with FOI, thorough knowledge of the airway anatomy and the ability to obtain clear views of the field are the cornerstones for effective fiberoptic endoscopy.
Additional equipment essential for safe and successful FOI is listed in Table 3 (see also Figure 3).
Six movements are possible with FOB: forward or backward, up or down in the vertical plain and left/right rotation.The easiest FOI technique is described as "up-downup", which means advancing the FOB forward, ante flexion under the epiglottis and upward at the level of the anterior commissure 12 .FOB with diameter of 4.1 mm can be used  for placement of an endotracheal tube (ETT) with diameter 5 mm or a double lumen tube size 37 or greater.A smaller diameter FOB should be used for placement of ETT 4.5, in cases of specific pathological changes or in pediatric patients.
The standard FOB is ergonomically constructed for handling with the right hand.It is advised that proximal part of FOB is handled with the third, fourth and fifth finger of the right hand, while the second finger is on the suction port and the first finger is on the FOB commands.The left hand lies on the face of the patient and handles the distal part of the FOB like a pen.The FOB needs to remain straight, and bending should be avoided.The left hand is used to advance the FOB along the airway, but FOB movement should be slow, to allow recognition of the relevant airway structures.
In order to facilitate smooth movement, the outer surface of the FOB should be lubricated, and an anti-fogging substance should be used for lens clearance.In addition, the FOB should be connected to an external oxygen source, so that oxygen can be insufflated during FOI.Ideally, the ETT should be somewhat wider (but not much wider) than the bronchoscope, for optimal maneuverability.An ETT approximately 1.5 mm wider than the FOB is ideal, whereas a much wider ETT (i.e.9.0 ETT with 4.5 FOB) would make placement of the ETT more difficult.

Patient preparation
Depending on the clinical situation, patient age, comorbidities and specific airway problems, FOI can be performed with a patient being awake, sedated or completely anesthetized.Maintenance of spontaneous breathing is recommended in patients with difficult airway, whereas FOI under general anesthesia is generally preferred when FOI is used for education, in patients with normal airway anatomy.
Adequate oxygenation, provision of sedation without compromising spontaneous breathing and attenuation of laryngeal reflexes are important for successful FOI.Patients need to be informed about the FOI procedure, potential complications, and the possibility that tracheostomy may be needed 13 .
Preparation for FOI includes administration of an antisialogogue 20 min before the procedure (Table 4), in order to minimize secretions that can compromise the fiberoptic view.In our experience, scopolamine is an excellent antisialogogue.

Topical anesthesia
Lidocaine 4% can be used for topical anesthesia of the nose, mouth, pharynx and larynx (max dose 4 mg/kg) 14 .Absorption of nebulized lidocaine is 25%, and the peak effect occurs after 30 min 15 .
The trigeminal nerve innervates the nasal and oral mucosa, the upper part of the nasopharynx, the soft palate and the tonsils.Topical anesthesia of the mouth and oropharynx can be accomplished using a combination of benzocaine, tetracaine and butamben.A tongue blade can be used to apply pressure on the tongue and posterior pharynx, in order to evaluate whether topical anesthesia is adequate on all structures of interest 16 .Topical Lidocaine 4% has a rapid onset of effect (within one minute), reaches the peak effect after two to five minutes, and its duration of action is 30-45 minutes 17 .
Three types of regional blocks can be used in anesthesia of the upper airway 18 .The glossopharyngeal nerve innervates the posterior third of the tongue, the part of the soft palate, oropharynx and upper part of epiglottis 16 .Bilateral injection 2 ml of lidocaine 2% in the basal part of the tonsilar arch blocks the glossopharyngeal nerve and provides anesthesia of the oropharynx.The superior laryngeal nerve innervates the base of the tongue, the epiglottis, the piriformis fossa and the vallecula.It can be blocked with bilateral injection 2 ml of lidocaine 2%, caudal from the hyoid bone horns and the medial to the external carotid artery 16 .Laryngeal stimulation causes glottis closure.Superior laryngeal nerve block provides anesthesia of the larynx and trachea under the vocal cords.Translaryngeal block is performed with injection of 4 ml lidocaine 4% with a 22 G needle through the cricothyroid membrane 16 .After aspiration of air confirms that the needle is in the trachea, lidocaine can be injected to block the recurrent laryngeal nerve and the superior laryngeal nerve 15 .However, because of concerns about complications such as tracheal injury, bleeding and subcutaneous emphysema, translaryngeal blocks are rarely used.
If the nasal route is used for FOI, vasoconstrictor and application of local anesthetic in the nasopharynx is also necessary.
The standard monitoring is mandatory during FOI (Table 3), but additional monitoring may be needed, depending on patient condition and comorbidities.During FOI, the patient can be in the sitting, semi-sitting or supine position.FOB can also be used with the patient in the prone or lateral decubitus position 19 in rare situations where urgent intubation is necessary.Chin lift, jaw thrust or pulling of the tongue may be necessary in order to facilitate visualization of the vocal cords in such cases.

Sedation
Adequate (but not excessive) sedation is important, in order to safely provide good intubating conditions with minimal cough or patient movement, while maintaining patient comfort, amnesia and anxiolysis.A variety of newer and older sedative agents can be used for sedation during FOI (Table 5), and the depth of sedation can be monitored using the Ramsay Sedation Scale (aiming for scores 2), entropy or BIS monitoring.
Fentanyl and alfentanil should be used with great caution as sedative agents, because they can cause respiratory depression 20,21 .Remifentanil, having very favorable characteristics for sedation during FOI 22 , can be administered by target controlled infusion (TCI) (0.8 ng/mL) or manual controlled infusion (0.75 μg/kg and 0.075 μg/kg/min).Published data suggest that remifentanil can confer better hemodynamic stability and intubating conditions when administered by TCI 22 .
Propofol administered by TCI and sevoflurane can also provide high degree of success during FOI 23 .However, compared to propofol, remifentanil seems to confer better conditions for endoscopy and intubation 24 .
Dexmedetomidine, combined with small doses of midazolam, is particularly effective in providing adequate sedation while preserving spontaneous respiration during FOI in patients with difficult airway 25,26 .A combination of dexmedetomidine with midazolam (0.02 mg/kg) can achieve better patient cooperation compared with midazolam only (0.05 mg/kg) 27 .

Orotracheal FOI
FOI can be performed through the mouth with use of specially designed oropharyngeal airways.The oropharyngeal airway can be placed when the patient is sedated, and can serve as the conduit for passage of the FOB during FOI.Several types of oropharyngeal airways are commercially available for FOI, and their role is to provide better control of FOB position and protect the FOB and patients' teeth (Figure 4).As the FOB advances, the base of the tongue is the first visible structure, and then the epiglottis can be visualized.Then, careful advancement of the FOB under the epiglottis reveals the anterior commissure.With the glottis in the center of the picture, the aryepiglottic folds, vestibular folds, vocal chords and opening of the larynx into the trachea can be clearly seen (Figure 5).Then, as the FOB advances through the vocal chords, visualization of the tracheal rings confirms that the FOB has entered the trachea.The FOB should be advanced, until the tip of the FOB is located three to five centimeters above the carina, in order to facilitate appropriate placement of the ETT.The ETT is then advanced gently over the FOB, using the right hand.The cuff of the ETT is inflated after visual confirmation of proper ETT position above the carina, and the FOB is removed.Finally, the ETT is connected to the circuit of the anesthesia machine, and endotracheal placement is also confirmed by capnography and by auscultation for bilateral breath sounds.

Nasal FOI
Nasal FOI conducted through a nasopharyngeal tube, and is probably the easiest method for reaching the vocal cords.Nasal intubation is contraindicated in the presence of base of the skull fractures, brain tumors, coagulopathy, nasal obstruction, tumors localized in the epiglottis and bacteremia 28 .
During nasal FOI, the ETT is lubricated with gel and is then advanced through the nostril until the cuff of the ETT disappears.Then, the ETT serves as a conduit for advancing the FOB.After the FOB passes through the nasopharynx pass, the uvula and the base of the tongue can be seen.Then, as the FOB advances further, the epiglottis, the ariepiglotic folds and parts of the glottis parts can be seen.

Additional equipment to facilitate FOI
FOI is considered a "low complexity skill" in modern anesthesia practice: it is a critical part of difficult airway guidelines 29 , and its failure rate in experienced hands is around 1.2% 30 .There are several different techniques for "low complexity skill" FOI.Low skill FOI is achieved by passing a FOB loaded with an aintree intubation catheter (AIC, Cook UK, Letchworth, Herts, UK) through laryngeal mask (LMA) which had already been placed to maintain the patient's airway 31,32 .After FOI, the removal of the LMA over the ETT is impaired by the short length of the ETT, easily resulting in tube dislocation from the trachea.Among several techniques to overcome this problem, Arndt tube exchanger (Arndt Airway Exchange Catheter Set, Cook Critical Care, Bloomington, Indiana) offers a reliable method not only for safe removal of the laryngeal mask over the tracheal tube but also for insertion of an adequate tracheal tube, particularly in pediatric patients 32,33 .
Placement of LMA without grids or intubating LMA (ILMA) provides oxygenation, ventilation and guides ETT.Use of ILMA (LMA-Fastrach™ , LMA North America, Inc., San Diego, CA) is the best for FOI.The first step is to remove a connector from the ETT.Then, an ETT size 6.0 can be placed through LMA size three or four.FOI through LMA involves several steps 34 : First, the ETT is placed inside the LMA.When the ETT reaches the epiglottis elevator, the FOB is advanced through the ETT, and then through the vocal cords, into the trachea.Then, the ETT is advanced over the FOB to the trachea.The size of the ETT is important during this procedure: the ETT should be at least 6 mm, because a smaller ETT cannot lift the epiglottis elevator 34 .
A rigid video laryngoscope (RVL) can also be very useful when used in combination with the FOB during FOI, because it helps open the oropharynx and minimize FOB lateralization 35 .After anesthesia induction, the RVL is used to visualize the upper part of the larynx, and then the FOB is placed in front of the glottis 36 .The assistant holds the FOB, which is then advanced through the vocal cords, and then the ETT is advanced over the FOB into the trachea.This technique combines two fiberoptic views: an external view through the RVL and an internal view through the FOB.

FOB for single lung ventilation
Intubation with a double-lumen endotracheal tube using FOB is possible, but extremely difficult, due to the construction and the small size of the double-lumen tube 37,38 .Therefore, when lung isolation is needed, airway experts recommend placing a regular ETT through the FOB and then either use a bronchial blocker, or exchange from a regular ETT to a double-lumen ETT using a tube exchanger [38][39][40] .

FOI complications
FOI complications are usually the consequence of excessive sedation or inadequate technique 41 .The most important complications are listed in Table 6.

Extubation after FOI
Criteria for extubation of the trachea include hemodynamic stability, the return of protective airway reflexes, adequate spontaneous respiration, and the absence of significant airway edema.However, when extubating a patient with a difficult airway, the FOB should be readily available, in case an airway emergency occurs.Placement of an endotracheal tube exchanger through the ETT, so that the exchanger remains in place for some time after extubation, can be extremely helpful if reintubation is needed.

FOB maintenance
Endoscopes used for FOI are potential sources of infection, and therefore should be cleaned thoroughly after each use.Proper cleaning of a FOB with a special brush and water can effectively remove 99.9% of microorganisms.Glutaraldehyde is the agent most frequently used for sterilization and removal of spores.Following proper sterilization, a FOB can be stored in a straight hanging position or in special boxes.

Conclusion
Because of insufficient training, anesthesiologists rarely use FOI, even in situations when the use of FOI is clearly indicated.Proper patient and airway preparation enables fast and easy recognition of airway structures, followed by safe, timely ETT placement with minimal patient discomfort.Ongoing education and practice with FOI are necessary in order to enhance safety while managing patients with difficult airways.

Fig. 2 -
Fig. 2 -The recently presented fiberoptic bronchoscope with a built-in camera, light source and 2.5 inch monitor (Olympus MAF type TM Olympus Medical Systems Corporation, Tokyo, Japan)

Fig. 3 -
Fig. 3 -The fiberoptic bronchoscope and the accompaning airway equipment for difficult airway management

Fig. 5 -Fig. 4 -
Fig. 5 -View through the fiberoptic bronchoscope video laryngoscope: the glottis can be seen at the center of the picture

Table 2 Contraindications to fiberoptic intubation
Expected difficult mask ventilation (if a user is not familiar with extraglottic device which can be used for ventilation) Massive upper airway hemorrhage Upper airway obstruction Risk for regurgitation or vomiting (if a user is not familiar with the procedure for awake intubation) Inexperienced anesthesiologist Strana 63 Slavkovi Z, et al.Vojnosanit Pregl 2013; 70(1): 61-67.