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\begin{document}

\title{Anesthetic management of airway stent placement by rigid bronchoscopy
with superior laryngeal nerve block while preserving spontaneous
breathing: a case report}



\author[1]{Toshio Okada}%
\author[1]{Mio Yoshida}%
\author[1]{Tomoko Matsushita}%
\author[1]{Yusuke Ishida}%
\author[2]{Kinya Furukawa}%
\author[2]{Michihiro Murozono}%
\affil[1]{Tokyo Medical University}%
\affil[2]{Tokyo Medical University Ibaraki Medical Center}%


\vspace{-1em}



  
  \date{May 15, 2024}


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\textbf{Anesthetic management of airway stent placement by rigid
bronchoscopy with superior laryngeal nerve block while preserving
spontaneous breathing: a case report}

Toshio Okada\textsuperscript{1)}, Mio Yoshida\textsuperscript{1)},
Tomoko Matsushita\textsuperscript{1)}, Yusuke
Ishida\textsuperscript{1)}, Kinya Furukawa\textsuperscript{2)}, and
Michihiro Murozono\textsuperscript{3)}

1) Department of Anesthesiology, Tokyo Medical University, 6-7-1
Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan

\par\null

2) Department of Thoracic Surgery, Tokyo Medical University Ibaraki
Medical Center, 3-20-1 Chuo, Amimachi, Inashiki-gun, Ibaraki 300-0395,
Japan

3) Department of Anesthesiology, Tokyo Medical University Ibaraki
Medical Center, 3-20-1 Chuo, Amimachi, Inashiki-gun, Ibaraki 300-0395,
Japan

\textbf{Corresponding author:} Toshio Okada

Department of Anesthesiology

Tokyo Medical University

6-7-1 Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan

Tel.: +81-03-3342-6111; Fax: +81-03-5381-6650

Email: okd.shinjuku@gmail.com



\textbf{Abstract}

Anesthetic management of endobronchial stent placement by rigid
bronchoscopy requires the maintenance of spontaneous breathing while
suppressing upper airway reflexes. The combination of superior laryngeal
nerve block (SLNB) can reduce the respiratory depression that occurs
during management under total intravenous anesthesia. The patient was
diagnosed as having lung cancer with invasion into the right middle
bronchus and stenosis of the right main bronchus on chest computed
tomography, and emergency airway stent placement was performed. Sedation
was initiated with propofol and dexmedetomidine, and ultrasound-guided
SLNB was performed after local anesthetic spraying into the oral cavity
and trachea. Bucking was minimally controlled during insertion of the
rigid bronchoscope. The patient's intraoperative hemodynamics remained
stable, and there were no hypoxic events. SLNB can provide the
suppression of the upper airway reflex while minimizing effects on
spontaneous breathing, and may be useful for achieving balanced
anesthesia during rigid bronchoscopy.

\textbf{Keywords}

Superior laryngeal nerve block, Spontaneous breathing maintenance, Air
way stent



\textbf{Key clinical message}

The combination of superior laryngeal nerve block can reduce the
respiratory depression that occurs during management under total
intravenous anesthesia.

\textbf{Background}

Tracheobronchial stenting is a type of interventional respiratory
therapy. In anesthesia management for rigid bronchoscopy, it is
necessary to maintain an appropriate depth of anesthesia while
maintaining spontaneous breathing. The usefulness of superior laryngeal
nerve block (SLNB) in awake intubation is well known {[}1{]}. Recently,
the usefulness of SLNB in airway stent insertion has been recognized,
but there are few reports of ultrasound-guided SLNB. In a previous
report, the combination of SLNB and total intravenous anesthesia (TIVA)
reduced the respiratory depression associated with the use of propofol
and fentanyl in anesthesia for rigid bronchoscopy {[}2{]}.
Ultrasound-guided SLNB may be useful for reducing the dose of
intravenous anesthetics, by reducing airway reflexes. We here report a
case of a patient with airway stenosis caused by lung cancer, who
underwent tracheal stent placement under rigid bronchoscopy. TIVA
combined with ultrasound-guided SLNB enabled safe anesthetic management
without any adverse events. We obtained written informed consent from
the patient to publish this case report.

\textbf{Case presentation}

A 74-year-old man presented with a cough persisting for 2 months and
weight loss. A chest computed tomography scan displayed a 45-mm-long
mass lesion in the right lung at the end of
S\textsuperscript{9}--S\textsuperscript{10}, enlarged lymph nodes (35
mm) below the tracheal bifurcation, and infiltration in the right middle
bronchus. The right main bronchus was stenotic (Fig. 1), which could
lead to atelectasis, hence the patient was admitted to our hospital for
emergency endobronchial stenting.

After entering the operating theater, the patient's vital signs were
recorded as follows: oxygen saturation, 99\% under room air; blood
pressure, 176/82 mmHg; and heart rate, 62 bpm. In the supine position,
the patient had no respiratory distress. Oxygenation (6 L/min) was
started using an oxygen mask. Anesthesia was induced by TIVA combined
with propofol and dexmedetomidine. Propofol was administered by
target-controlled infusion (TCI) with a
Terufusion\selectlanguage{ngerman}\textsuperscript{®}Syringe Pump (Terumo Co., Tokyo, Japan).
Dexmedetomidine administration was started at 0.6 \selectlanguage{greek}μ\selectlanguage{english}g/kg/h. After
intravenous infusion of 50 \selectlanguage{greek}μ\selectlanguage{english}g of fentanyl, 5 mL, and 2.5 mL of 4\%
lidocaine were sprayed into the space between the pharyngeal wall and
the glottis and into the trachea, respectively, using a McGrath
MAC\selectlanguage{ngerman}\textsuperscript{®} video laryngoscope (Medtronic Co., Minneapolis,
MN, USA). A pillow was placed under the patient's shoulder to maintain
neck extension, and the linear probe (13--6 MHz) Sonosite SII (Fujifilm
Sonosite, Inc., Bothell, WA, USA) was placed in the parasagittal plane
of larynx to identify the thyroid cartilage, thyrohyoid muscle,
thyrohyoid membrane, and hyoid bone (Fig. 2). Next, a hockey stick-type
probe (13--6 MHz) was used to identify the greater horn of the hyoid
bone, and then SLNB was performed using a 23-gauge, 60-mm needle and a
5-mL syringe in the sagittal approach under real-time ultrasound
guidance (Fig. 3 A, B). Lidocaine (2 mL of a 2\% solution) was injected
to each side of larynx, and no bleeding was confirmed after compression
for 5 minutes after the SLNB. After confirming the anesthetic procedure,
the bispectral value remained about 60 and spontaneous breathing was
maintained, a rigid bronchoscope was inserted by a respiratory surgeon.
There was almost no bucking during insertion. Spontaneous breathing was
maintained throughout the procedure, and pure oxygen was supplied
through the side port of the rigid bronchoscope. The stenosis was
balloon dilated and a 9-mm silicone stent was inserted. There was little
body movement during insertion of the rigid speculum alone, but when
endotracheal manipulation was performed, bucking was observed, so a
total of 3 mL of 2\% lidocaine was intermittently administered into the
trachea. Intraoperative hemodynamics remained stable throughout the
operation, even though no additional fentanyl was administered. The
endoscopic procedure was completed without any adverse events, and the
rigid bronchoscope was removed. SpO\textsubscript{2} was maintained at
97\% to 100\% during the anesthesia. The operation time was 1 hour 55
minutes. There were no complications such as tracheal bleeding or vocal
cord paralysis after the surgery.

\textbf{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 \selectlanguage{greek}μ\selectlanguage{english}g/kg/h) and propofol by
TCI (1.0--2.0 \selectlanguage{greek}μ\selectlanguage{english}g/mL) to maintain a sedation level that maintains
spontaneous breathing. In recent years, dexmedetomidine, which is a
central \selectlanguage{greek}α\selectlanguage{english}\textsubscript{2}-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.

\textbf{List of abbreviations}

SLNB: superior laryngeal nerve block

TIVA: total intravenous anesthesia

TCI: target-controlled infusion

\textbf{Declarations}

\textbf{Ethics approval and consent to participate}

Not applicable

\textbf{Consent for publication}

Written informed consent was obtained from the patient for publication
of this case report and the accompanying images.

\textbf{Availability of data and material}

Not applicable

\textbf{Competing interests}

The authors declare that they have no competing interests associated
with this manuscript.

\textbf{Funding}

None

\textbf{Authors' contributions}

TO contributed to the anesthesia management of the patient,
conceptualization of the case report, and writing of the original draft.
MY, TM, and YI contributed to the anesthesia management of the patient.
KF edited the manuscript. MM was the overall supervisor of this case.
All authors read and approved the final version of the manuscript.

\textbf{Acknowledgements}

The authors would like to thank H.A. Popiel for English language
editing.

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\textbf{Figure legends}

\begin{CJK}{UTF8}{gbsn}\textbf{Fig.1　Chest computed tomography on admission}\end{CJK}\selectlanguage{english}

Each image displays a mass lesion in the right lower lung field and
enlarged lymph nodes below the tracheal bifurcation. The arrow indicates
stenosis of the right middle bronchus.

\begin{CJK}{UTF8}{gbsn}\textbf{Fig.2　Ultrasound images of structures around the superior
laryngeal nerve}\end{CJK}\selectlanguage{english}

Thyroid cartilage (A), hyoid bone (B), thyrohyoid muscle (C), and
thyrohyoid membrane (D) are marked on the ultrasound image. The Yellow
dotted circle represents the space of the superior laryngeal nerve.

\begin{CJK}{UTF8}{gbsn}\textbf{Fig.3　State at the superior laryngeal nerve block}\end{CJK}\selectlanguage{english}

Image of actual implementation of the superior laryngeal nerve block
(A), and a real-time ultrasound image of the nerve block (B). The
superior laryngeal nerve block was performed in the sagittal plane under
real-time ultrasound guidance. The tip of the needle (indicated by the
arrowheads) was positioned around the greater horn of the hyoid bone.

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