Discussion
An airway stent is an artificial organ that expands and supports the lumen of the trachea and bronchi, or closes a fistula, in patients with central airway stenosis. There are 2 types of airway stents currently available in Japan, i.e., silicone stents and self-expandable metallic stents [3], and silicone stent implantation is widely accepted as requiring rigid bronchoscopy under general anesthesia [4].
In general, anesthesia management for rigid bronchoscopy is performed by the following 2 methods: one is to maintain the patient’s spontaneous breathing, and the other is to administer muscle relaxants and perform controlled breathing. In high-risk patients, such as those with bronchopleural fistulas, treatment with extracorporeal membrane oxygenation has been reported [5]. Although there is a study report that the incidence of hypoxic events was lower in the controlled breathing group [6], as the silicon cap of the rigid scope head is removed during the procedure, this may cause apnea in patients undergoing controlled ventilation. Therefore, at our institution, anesthesia is managed in most patients while maintaining spontaneous breathing.
In a report of TIVA assisted by ultrasound-guided SLNB and lidocaine endotracheal spray for rigid bronchoscopy, stable spontaneous breathing was maintained during operation without laryngospasm, bucking, or desaturation, and no perioperative pulmonary or cardiovascular complications were observed [2]. SLNB is often used in awake intubation, similar to rigid bronchoscopy. SLNB in awake fiber intubation is more advantageous than the spray method alone, in terms of the time required for intubation and patient satisfaction [7] [8]. In the case of awake fiber intubation, similar results were obtained in patients treated with SLNB and patients treated with continuous remifentanil alone [9]. SLNB has also been applied clinically for the treatment of neurogenic cough [10]. In our institution, SLNB is performed when the following criteria are met:1) the patient does not complain of respiratory distress in the supine position, 2) there is no anatomical abnormality in the appearance of the patient’s neck, and 3) the preoperative ultrasound pre-scan shows a typical image.
The superior laryngeal nerve is a branch of the vagus nerve, and its external branch controls cricothyroid muscle movement, and the internal branch controls the sensation of the laryngeal mucosa above the level of the vocal cords, including the root of the tongue and the epiglottis [8, 11, 12]. Therefore, preoperative and intraoperative spraying of local anesthetic is necessary for anesthesia to suppress the reflex of the trachea. The superior laryngeal nerve runs posterior to the carotid artery, passing through the lateral side of the hyoid bone, and the medial branch passes just below the greater horn of the hyoid bone, approaching the thyrohyoid muscle with the superior laryngeal artery [13, 14], and then penetrates the thyrohyoid membrane [12, 15, 16]. Autopsy results have demonstrated that there is a space between the hyoid bone and the thyroid cartilage, which contains the internal branch of the superior laryngeal nerve [17]. By placing a linear ultrasound probe in the parasagittal plane under the jaw, the greater horn of the hyoid bone, thyroid cartilage, thyrohyoid membrane, and thyrohyoid muscle can be identified, and the internal branch of the superior laryngeal nerve is detected between the hyoid bone and thyroid cartilage[12, 18-20]. Reported complications of SLNB that was performed blindly include unilateral visual impairment with left facial numbness and hearing loss [21]. Therefore, SLNB performed under real-time ultrasound guidance is preferable.
When performing rigid bronchoscopy operation at our institution, we start anesthesia with dexmedetomidine (0.5–0.7 μg/kg/h) and propofol by TCI (1.0–2.0 μg/mL) to maintain a sedation level that maintains spontaneous breathing. In recent years, dexmedetomidine, which is a central α2-adrenoceptor agonist, has increasingly been used in postoperative intensive care units for sedation and analgesia [3]. Dexmedetomidine has also been shown to be useful as a sedative agent that does not cause respiratory depression [22], and for maintaining sedation during intubation [23]. It acts on part of the circuitry that governs natural sleep, and is similar to normal physiological sleep[24]. Propofol is equally effective, but the risk of airway obstruction and hypoxic events is higher than for dexmedetomidine [25].
Regarding anesthesia for rigid bronchoscopy, a combination of TIVA and SLNB might be enable avoiding the use of opioids and propofol, and reduce the risk of respiratory depression, but further studies are needed to confirm its usefulness. The location of the superior laryngeal nerve can easily be visualized by ultrasound, and the procedure is simple. Therefore, the combination of TIVA and SLNB may be useful for achieving balanced anesthesia for rigid bronchoscopy.