Introduction:
Awake tracheal intubation (ATI) has a high success rate and a low-risk profile, and it has been referred to as the gold standard in airway treatment for difficult airways. This has historically been done using flexible bronchoscopy, but more recently with awake video laryngoscopy.
In patients with various conditions (for example, atlantooccipital disease, small mandibular space, head and neck tumors with previous radiation, obesity due to sleep apnea), challenging or impossible ventilation and tracheal intubation can be expected.
Induction of anesthesia in these patients can eventually result in potentially fatal airway obstruction. It is critical to understand the anatomy and morphology of the normal upper and lower airways, from the nasal tube to a ridge at the base of the trachea (windpipe) or to the bifurcation of the trachea.
It is also necessary to understand the mechanisms of action and maximal doses of several local anesthetic agents and vasoactive medications, as they are extensively utilized in this procedure. It is critical to recognize the indications and symptoms of local anesthetic poisoning and treat it. Moreover, the anesthetist should have a management strategy for handling any challenging airway event, whether planned or unexpected.
Multiple attempts to secure the airway can exacerbate the problem. Hence it is best to intubate the airway in an awake patient when trouble is expected. Unfortunately, competent anesthesiologists may wrongly avoid awake intubation despite clinical indications and a favorable safety and success record.
What Are the Reasons for Awake Tracheal Intubation?
The reasons for avoiding awake intubation are not always evident; however, various probable justifications exist.
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Firstly, practitioners may be concerned about patient anxiety or pain during awake intubation. In the instance that a patient exhibits a reluctance to the approach during the preoperative consultation. In that case, this might lead to avoiding the method from the start or deviating from an initial plan of awake intubation.
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Secondly, the airway must be anesthetized to execute effective awake intubation. This procedure takes expertise and can be time-consuming. In addition, the operation room itself is under production pressure.
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Thirdly, bronchoscopy skills are challenging to acquire and are prone to decay, which may cause discomfort to the practitioner with awake flexible bronchoscopy if not constantly performed.
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Finally, awake intubations may be high-risk if they cause a marked sympathetic reaction.
What Is the Role of Local Anesthetics in Awake Intubation?
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The effectiveness of awake tracheal intubation is mainly based on proper airway topicalization. Using a vasoconstrictor in the nasal passages before nasotracheal intubation reduces the incidence of epistaxis.
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Cocaine, the sole local anesthetic with vasoconstrictor characteristics, is beneficial for topical nasopharyngeal anesthesia. It is available as a solution or a paste, and the maximum suggested dose is 1.5 mg per kg; however, care should be taken before use in individuals with hypertension, pseudocholinesterase deficiency, and coronary artery disease.
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The delivery mechanism used, including but not limited to mucosal atomization, the spray-as-you-go (SAYGO) approach, transtracheal injection, and nebulization can cause inconsistent local anesthetic absorption. There is insufficient data to suggest one method superior to another.
What Is the Role of Sedation in Awake Intubation?
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A complete sedation technique for ATI should comprise anxiolysis, forgetfulness, limited or no recollection, adequate analgesia, and cough and gag reflexes suppression.
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It is critical to note that sedation should not be employed to compensate for inadequate airway topicalization. Excellent airway anesthesia may eliminate sedation, allowing for better patient participation.
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Oversedation should be avoided since it can result in respiratory depression, hypoxia, hypercarbia, loss of airway, cardiovascular instability, and aspiration. While another physician attempts ATI, it may be good to have an impartial anesthesia practitioner monitor and titrate sedation.
What Is the Airway Anatomy and Airway Blocks?
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Upper airway anesthesia is performed by inhibiting sensation in the nasal and mouth canals. The trigeminal nerve (cranial nerve V) offers sensory innervation to the nose.
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In contrast, the lingual nerve (V) serves the anterior two-thirds of the tongue, and the posterior 1/3 of the tongue is supplied by the glossopharyngeal nerve (IX) supplies.
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The glossopharyngeal nerve (cranial nerve (CN) IX) and the vagus nerve provide sensory innervation to the pharynx (CN X). The superior laryngeal nerve (CN X) innervates the larynx above the vocal cords, whereas the recurrent laryngeal nerve (CN X) innervates the vocal cords and trachea below the vocal cords. The vagus nerve supplies the trachea (CN X).
When topical anesthetic fails or is inadequate for ATI, nerve blocks such as a glossopharyngeal nerve block, superior laryngeal nerve (SLN) block, and transtracheal block are used. These blocks are not recommended for people who have coagulopathies. To avoid intravascular injection, which can cause nerve damage, convulsions, and trauma, aspiration should be started before local anesthetic deposition. By enhancing the precision of local anesthesia deposition, ultrasound can be an effective tool for increasing the success rate of airway blocks. In addition, the larger cornua of the hyoid bone for the SLN block and the cricothyroid membrane for the transtracheal block can be identified using ultrasound.
What Are the Blocks Used during Awake Intubation?
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Glossopharyngeal Block.
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Superior Laryngeal Block.
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Transtracheal Block.
What Is Airway Topicalization?
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Besides airway blocks, there are other approaches for topicalizing (anesthetizing) the upper airway in preparation for ATI. Coughing, gagging, and laryngospasm are all airway responses that inhibit effective airway management.
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To anesthetize the oropharynx, atomized Lidocaine is usually used. A cannula with four percent Lidocaine laryngotracheal anesthesia (LTA) can be utilized as an intubation adjuvant to probe and topicalize the airway during direct or video laryngoscopy.
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Because of the potential risk of methemoglobinemia, a topical anesthetic with tetracaine and benzocaine is avoided. Instead, the McKenzie method or a mucosal atomization apparatus can directly spray a local anesthetic into the nasopharynx and oropharynx.
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In the McKenzie procedure, a 20-gauge cannula is linked to oxygen tubing through a three-way stopcock that provides a flow rate of two to four liters per min. When the local anesthetic is injected with a syringe, a jet-like spray is produced, allowing for efficient topicalization of the nasal and oral mucosa.
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Patients can gargle two percent viscous Lidocaine, apply Lidocaine paste, or use pledgets soaked with Lidocaine. Furthermore, utilizing an oxygen-driven power sprayer, four percent Lidocaine may be delivered to glottic and oropharyngeal structures.
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In patients with restricted mouth opening, four percent Lidocaine can be injected into a nebulizer and administered with oxygen for thirty minutes as an effective and noninvasive method of airway topicalization down to the trachea.
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Local vasoconstriction is required for a nasotracheal intubation method to limit the possibility of epistaxis, which can compromise effective airway instrumentation.
Conclusion:
Various factors influence safety and efficacy of airway topicalization for ATI, including sufficient sedation, adequate local anesthetic administration, use of complex airway equipment, and practitioner level of skill and experience. Training with alternate airway devices, enhanced capnography and patient monitoring, and improved local anesthetic administration devices are some strategies for improving ATI. Further research is needed to improve clinical and patient-centered outcomes in patients with difficult airways.
