Awake fibreoptic intubation
*Paweł Andruszkiewicz, Marta Dec, Andrzej Kański, Robert Becler
2nd Department of Anaesthesiology and Intensive Therapy, Medical University of Warsaw
Awake fiberoptic intubation has been recommended for adult patients with a difficult airway in whom anaesthesia and/or relaxation could lead to the “cannnot ventilate, cannot intubate” situation.
We describe the strategy and protocols of such management in cases with a predicted difficult airway.
The described method is safe and effective, and can be recommended for cases where there is serious doubt about the possibility of maintaining an open airway during induction of anaesthesia, or in cases where intubation has failed during previous anaesthesia. Awake intubation is rarely associated with serious episodes of desaturation and it is usually well tolerated by motivated patients.
Endotracheal intubation-related complications are a frequent cause of deaths associated with general anaesthesia [1, 2]. Failed attempts of intubation may lead to hypoxia and subsequent brain damage. For these reasons, intubation is still considered the procedure carrying a high risk of potential complications despite an increasingly wide range of devices available for this purpose (e.g. fibreoptic guides and video laryngoscopes).
In cases of unanticipated difficult intubations, the algorithms of management are essential [3, 4, 5], which should be known to each anaesthesiologist in training. In many cases, difficult intubation can be anticipated already during examinations of patients [3, 6]. The information about such risks should be included in the medical records or special charts, e.g. the flowchart designed by the Difficult Airway Society (DAS) . Facial skeleton anomalies caused by diseases and traumas should incline to particularly thorough assessment of the patients` airway [6, 8]. It is advised to objectivise the findings using the scales evaluating the extent of intubation difficulties.
In cases of anticipated difficult intubations, the ASA and many European authors recommend awake fibreoptic intubation [3, 6, 8, 9]. The asset of this method is a widened margin of safety thanks to maintenance of an open airway and spontaneous breathing.
The limited mouth opening and decreased mobility of the atlanto-occipital joint are common, e.g. in patients with rheumatoid arthritis. In some orthopaedic surgeries requiring the prone position, fibreoptic intubation is recommended before general anaesthesia . Another indication for this procedure is limited mouth opening in patients with oral abscesses. The use of a fibroscope is also advised in patients with cervical spine trauma. In such cases, classic laryngoscopy is preceded by the removal of a neck collar and manual stabilization of the spine to avoid the spinal cord damage [10, 11]. Thanks to the fibroscope, the collar can be left in place throughout the procedure and the neurological condition assessed immediately after intubation .
Anaesthesiologists cooperating with laryngologists are frequently faced with difficulties in maintaining an open airway in patients with large tumours in the oral cavity and throat (often disintegrating) whose location and size prevent the use of classic laryngoscopes. In such cases, awake fibreoptic intubation through the nose enables relatively easy and safe bypassing of the obstacle.
According to some authors, further indications for this kind of intubation include obesity when the body mass index (BMI) exceeds 35 kg m-2, looseness of teeth, full-stomach procedures (when difficulties are anticipated), and cardiovascular high-risk patients [8, 9].
Training and achieving proficiency in the use of fibroscopes as well as in provision of anaesthesia for such procedures are essential. There is no doubt that the only way to gain adequate skills is regular training during scheduled procedures once the patient`s consent has been obtained .
Contraindications for the use of fibroscopes during intubation include the lack of consent or lack of cooperation of a patient. Moreover, it is believed that the procedure should not be used in patients with partially obstructed airways (e.g. tumours in the true glottis region) as in such cases incidents of increased dyspnoea or complete airway obstruction have been described. The insertion of a fibroscope through the nose is also not advised in cases of liquorrhoea, nasal bone fractures, tumours of the nasopharynx and severe clotting abnormalities (bleeding hinders the visualization of anatomical structures). A rare contraindication for the use of this method is allergy to local anaesthetics [6, 8, 9].
The success of the procedure depends largely on efficient anaesthesia of anatomic structures, which the fibroscope contacts with, and adequate sedation. Since the procedure may cause some discomfort, patients should be informed about its course and possible unpleasant sensations accompanying it (cough, dyspnoea, etc.).
Falling back of the tongue and soft palate limits the visibility during the insertion of a fibroscope. Therefore, the procedure is easier in a conscious and cooperating patient who can bend the head backwards and stick out the tongue to open the airway facilitating the fibroscope navigation. In recent years, many methods of regional anaesthesia were designed which enable awake fibreoptic intubation [6, 8]. In some, the mucous membranes are topically anaesthetized, in the others the suitable nerves are blocked . In the majority of cases, regional anaesthesia is supplemented with shallow sedation using intravenous anaesthetics, benzodiazepines and opioids.
The fibroscope insertion through the nose or mouth is preceded by topical anaesthesia of mucous membranes of the nasal cavity, pharynx and larynx [6, 8, 9]. The anaesthesia of this region can be provided administering 2-4% lignocaine solution in nebulization through the face mask, remembering that the efficacy of the preparation increases with its concentration . During the fibroscope insertion it is supplemented with visually guided topical anaesthesia of subsequent anatomical structures. For this purpose, the epidural catheter is introduced into the working channel in such a way that its outlet is adjacent to the distal end of the fibroscope. The solution of 1-4% lignocaine is administered through the catheter [13, 14]. This method involving spraying of the anaesthetic during administration is called the spray-as-you-go (SAYGO) method [6, 8, 9].
A serious problem, which may occur during the insertion through the nose, is bleeding. Therefore, before the procedure, vasoconstricting agents are used, mainly adrenaline added to lignocaine in the concentration ranging from 1:100 000 to 1: 200 000. Xylometazoline hydrochloride as 0.05% or 0.1% solution is also frequently used. Moreover, the preparation of lignocaine with phenylephrine is used, which is administered to the nose through the sprayer. In Great Britain, nasal mucous membranes are anaesthetized with 4% cocaine introduced to the nose on the cocaine-soaked swabs [6, 8]. The attempts to anaesthetize the nasal mucous membranes with lignocaine in gel are not encouraging as the gel adheres to the fibroscope optics worsening the picture quality.
Effective anaesthesia of the oral and pharyngeal mucous membranes is provided using the methods mentioned (nebulization and SAYGO) or rinsing the throat with lignocaine solution. However, they may not be sufficient to blunt the reflex from the posterior pharyngeal wall, which makes the insertion of the fibroscope through the mouth more difficult. In such cases, blockage of appropriate nerves is necessary bearing in mind that 2/3 of the tongue is innervated by the tricuspid nerve and its posterior part and the pharynx – by the facial (VII), glossopharyngeal (IX) and vagus (X) nerves. The tongue branches of the IX nerve innervate the pre-epiglottic fossae, anterior epiglottis as well as glossopalatine and pharyngeal folds. The blockage is provided by injecting 2% solution of lignocaine (from both sides) to the glossopalatine fold (anterior access) or palatine-pharyngeal fold (posterior access) . Another option for IX nerve blockage is the access near the styloid process .
The supra-epiglottic region may be easily anaesthetized using nebulization and throat rinsing described earlier. It is stressed that the SAYGO method enables the insertion through the true glottis once the patient stops to cough in response to spraying the vocal cords with an anaesthetic . The supra-epiglottic tissues of the larynx are supplied by the superior laryngeal nerve, which is the branch of the vagus nerve (X). Its final internal sensory branches lead to the tongue, true glottis, arytenoid-epiglottal folds and the mucous membrane around vocal cords (vocal cords excluded). In some cases, the superior laryngeal nerve is blocked by administering 2 mL of 2-4% lignocaine to the space between the thyroid and mucous membranes of the larynx (the needle is inserted between the superior horn of the thyroid cartilage and the greater horn of the hyoid bone). The blockage may, however, be associated with severe complications, e.g. intravascular administration of the agent or paralysis of vocal cords.
Vocal cords and laryngeal mucous membrane are supplied sensorially by the recurrent laryngeal nerve (branch X). The anaesthesia of this region is provided using the SAYGO method and injecting vigorously 2-5 mL of 2-4% lignocaine to the larynx through the cricothyroid membrane during the expiratory phase. The complications related to this method include glottis spasms and subcutaneous emphysema .
Fibreoptic intubation can be performed only under efficient local anaesthesia, which was demonstrated during the courses when their participants performed fibreoptic intubation in their colleagues .
During fibreoptic intubation, sedation is used to relieve anxiety, induce amnesia, eliminate pain and blunt protective reflexes (e.g. cough). Opioids and benzodiazepines or propofol are administered intravenously; their doses should be suitably adjusted to avoid excessive sedation and apnoea, which may be life threatening in difficult airway cases. . Fentanyl 50-100 µg and midazolam 1-5 mg have also been previously used yet abandoned. At present, remifentanil and propofol are preferred, administered by the TCI or TIVA method. The findings of recent studies demonstrate that remifentanil during fibreoptic intubation shortens the procedure and provides higher comfort  compared to propofol  and midazolam with fentanyl . The researchers from Austria designed the optimal model of remifentanil dosage: after injecting a single dose of 0.75 µg kg-1, the intravenous infusion should be started with the speed of 0.075 µg kg-1 min-1 . Dexmedetomidine is also used for sedation during fibreoptic intubati
on since it does not induce respiratory depression and has analgesic effects .
During fibroscopy, agents decreasing the amount of airway secretion and limiting mucous bleeding are important. With them, navigation of the endoscope is easier and local anaesthetics reach quicker their destination. Vasoconstricting drugs and agents blocking muscarinic receptors are used, most commonly glycopyrronium bromide, less commonly hyoscine and atropine. In the majority of cases, the drugs are administered intravenously 15 min before intubation; intramuscular administration is also possible 60 min before the procedure .
Awake fibreoptic intubation requires extreme accuracy to ensure maximal comfort of patients . In some centres, special courses are organized during which their participants perform endoscopies on their colleagues. Such trainings enable to understand better the feelings of patients. It was demonstrated that amongst 200 anaesthesiologists undergoing endoscopy trainings, only 4 found the procedure painful and definitely unpleasant. The manipulations of an endoscope and the resultant excitation of the sympathetic system manifested as increased SAP by over 20% in 23 % of respondents and as similarly accelerated HR in 59%. It is noteworthy that participants were not sedated . The procedure of intubation using a bronchoscope may be carried out without discomfort, which is confirmed by personal experience of one of the authors of the present paper (P. A.) who took part in such trainings.
Serious problems accompanying fibreoptic intubation (apart from those related to nerve blockage) are occasional symptoms of local anaesthetic intoxications. It was calculated that the total dose of lignocaine administered during nebulization and during the SAYGO method may reach 15 mg kg-1 . Not surprisingly, 37% of patients develop overdose symptoms (dizziness, nausea and vomiting) , although toxic levels of lignocaine are not exceeded . A substantial amount of an agent administered in nebulization is swallowed and broken down in the liver [14, 25]. It is recommended not to exceed the total lignocaine dose of 9 mg kg-1 [26, 27].
Another serious problem that may be observed during tracheal intubation is inability to insert the tube to the trachea even though the fibroscope is already present in its lumen . The likelihood of such incidents increases with increasing disproportion between the diameters of the tube and endoscope. In rare cases, fibroscopy may lead to complete obstruction of the airway . Therefore, before the initiation of the procedure, alternative rescue management should be considered. The other complications related to fibreoptic intubation include infections of the upper airway, nose bleeding (10%), and sore throat .
The provision of patients’ safety is essential for successful fibreoptic intubation. The anaesthetic station should be equipped with ready-to-use devices, drugs and monitors of vital signs according to the guidelines of the Polish Ministry of Heath and Social Welfare. In conscious patients, the procedure is carried out using flexible fibroscopes, 3-5 mm in diameter and armoured intubation tubes, 5-6 mm in diameter. In cases of oral intubation, the Bonfils rigid fibroscope may be used .
The induction of anaesthesia may be started once proper placement of the intubation tube in the trachea has been confirmed during the withdrawal of the fibroscope and auscultation of the lungs; capnography of the expired gases should also be performed. The administration of anaesthetics after insertion of the fibroscope to the trachea but before intubation is wrong. According to the literature data, in some cases the insertion of the intubation tube to the trachea was impossible or resulted in accidental slipping of the endoscope out of the larynx .
Awake fibreoptic intubation is the treatment of choice in cases with anticipated difficult tracheal intubation during classic laryngoscopy. Its asset is the maintenance of an open airway and spontaneous breathing. The procedure performed by trained anaesthesiologists is safe and well tolerated by patients. Awake fibreoptic intubation is considered an important skill, each experienced anaesthesiologist should have.
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