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.