We report on 5 patients who required awake fiberoptic intubation where sonographic visualization of the superior laryngeal nerve followed by accurate placement of local anesthetic around the nerve was successfully performed. Written informed consent for publication of this report was provided by all patients.
In all patients (Table 1), IV access was established followed by attachment of standard monitors (electrocardiogram, pulse oximetry, and noninvasive arterial blood pressure). Adjunctive sedation was not used to preserve airway muscle tone and eliminate the risk of airway obstruction. An initial ultrasound scan of the neck was performed by a consultant anesthesiologist who was experienced in ultrasound-guided regional anesthesia and had performed approximately 20 ultrasound-guided superior laryngeal nerve blocks. Subsequently, the neck was prepared aseptically with chlorhexidine. An 8- to 15-MHz hockey stick-shaped transducer (HST15-8/20 linear probe, Ultrasonix, Richmond, BC, Canada) was used to visualize key anatomical structures of the superior laryngeal nerve space.1,2 The greater horn of the hyoid was identified by placing the transducer in the sagittal plane. Subsequently the thyroid cartilage, thyrohyoid membrane, and superior laryngeal nerve were identified (Fig. 1). Once the superior laryngeal nerve was identified (Fig. 2), dermal anesthesia was provided by local anesthetic infiltration of the skin. Subsequently, a 3.8-cm 25-G needle was advanced under real-time ultrasound guidance toward the superior laryngeal nerve and 2 mL of local anesthetic injected around the superior laryngeal nerve in accordance with previous reports.3 Circumferential local anesthetic spread around the superior laryngeal nerve was achieved (Fig. 3) after which the superior laryngeal nerve block was repeated on the opposite side. After bilateral superior laryngeal nerve blockade, a Williams airway coated lightly with a small amount of 2% lidocaine jelly was inserted into the patient’s mouth to provide topical anesthesia of the mouth. The Williams airway coated with viscous lidocaine was used to bypass direct contact of the endoscope and endotracheal tube (ETT) with the posterior tongue and upper posterior pharynx and obviated the need for a glossopharyngeal nerve block. A fiberoptic endoscope was advanced through the orifice of the Williams airway toward the larynx. An ETT was advanced over the endoscope through the glottis and into the trachea. After this, general anesthesia was induced with propofol and maintained with sevoflurane. There were no complications during superior laryngeal nerve block such as inadvertent puncture of surrounding structures, vasculature, or hematoma.
An 88-year-old woman, ASA physical status IVe, with a history of ankylosing spondylitis experienced a fall resulting in an unstable fracture of T7 and T8 and a small intracranial subdural hematoma. She required posterior spinal (T6-T10) instrumentation and fusion. In addition to ankylosing spondylitis, she had coronary artery disease, hypertension, obstructive sleep apnea, hypothyroidism, and diabetes mellitus. She was known to be sensitive to opioids and had experienced a respiratory arrest complicated by aspiration pneumonia during a previous hospital admission. On examination, her airway was Mallampati IV with no movement of the cervical spine due to ankylosing spondylitis. She required general anesthesia with awake fiberoptic intubation. We did not use any sedation during the awake fiberoptic intubation because we assessed her as having a high risk of respiratory arrest given her recent head injury and known sensitivity to opioids. The patient consented to general anesthesia and awake fiberoptic intubation. Airway anesthesia was accomplished with bilateral superior laryngeal nerve blocks (2.5 mL of 2% lidocaine per side) and a small amount of viscous lidocaine applied to the posterior aspect of a Williams airway. She tolerated the awake intubation with a number 7 ETT. She had no reaction to airway stimulation except a cough when the ETT was passed into the lower third of the trachea.
A 46-year-old morbidly obese man, ASA physical status IVe, weight 127 kg, presented for incision and drainage of an open forearm fracture after a motor vehicle accident. His other injures included a closed head injury and cervical spine injury. He was wearing an Aspen C-spine collar. His hospital chart revealed a prior difficult laryngoscopy. He consented to an awake fiberoptic intubation. He received only 1 mg of midazolam IV for sedation. Airway anesthesia was accomplished with bilateral superior laryngeal nerve blocks (2.5 mL of 2% lidocaine per side). No other local anesthetic was applied. The patient tolerated awake fiberoptic intubation without any obvious sign of airway irritation.
A 62-year-old man, ASA physical status IVe, fell off a bicycle while riding intoxicated. He had experienced an unstable C5-6 fracture. His history was remarkable for alcohol and marijuana abuse. He presented for anterior cervical instrumentation and fixation. He required general anesthesia with awake fiberoptic intubation because of spine instability. He consented to bilateral ultrasound-guided superior laryngeal nerve blocks and awake fiberoptic intubation. Airway anesthesia was accomplished with bilateral superior laryngeal nerve blocks (3 mL of 2% lidocaine per side). He received no additional sedation or airway anesthesia. He tolerated awake fiberoptic intubation without any signs of airway stimulation.
A 19-year-old man, ASA physical status IIIe, had attempted suicide earlier in the day by drinking bleach and then jumping off a bridge. He required repair of open fractures of the mandible and maxilla. Other injuries included fracture of right humerus, small liver laceration, bilateral pneumothoraces, and chemical burn injuries of his tongue and upper airway. On examination, he had bilateral chest tubes. His airway was Mallampati III with considerable swelling of the soft tissues around the upper airway. Airway anesthesia was accomplished with bilateral superior laryngeal nerve blocks (2 mL of 2% lidocaine per side). No other airway local anesthetic was applied. He tolerated the awake fiberoptic intubation well. There were no signs of airway stimulation during the fiberoptic intubation except for a cough when the ETT and bronchoscope reached the lower third of the trachea.
A 24-year-old man, ASA physical status IVe, was involved in a motor vehicle accident, including being trapped in a burning vehicle. He presented for repair of an open fracture of the right femur. He also received airway burn injuries. He also had multiple facial fractures compounding the facial edema. The attending trauma and intensive care physicians asked for assistance with intubation. It was expected he would require prolonged intubation for airway protection due to the swelling from his airway burns. He was in mild-to-moderate respiratory distress on arrival to the operating room. It was determined that sedation might decrease his respiratory drive, and the airway burns and edema precluded topical anesthesia to the airway. Airway anesthesia was accomplished with bilateral superior laryngeal nerve blocks (3 mL of 2% lidocaine per side). Awake fiberoptic intubation proceeded uneventfully through a Williams airway with no signs of airway stimulation.
The superior laryngeal nerve is a branch of the vagus nerve that descends adjacent to the pharynx behind the internal carotid artery.4 It bifurcates into an external branch that provides motor innervation to the muscle and an internal branch that provides sensory innervation to the base of the tongue, epiglottis, and the mucous membrane of the larynx down to the vocal cords.5 The internal branch of the superior laryngeal nerve passes medially below the greater horn of the hyoid bone to pierce the thyrohyoid membrane just superior to the superior laryngeal artery. The superior laryngeal nerve can be blocked bilaterally just before it penetrates the thyrohyoid membrane.6 In combination with topical local anesthesia to the oropharynx or nares, the superior laryngeal nerve block can be expected to provide complete anesthesia of the upper airway, paralysis of the lingual radix, epiglottis, and cricothyroid muscle to facilitate awake intubation with suppression of the gag and cough reflexes.4
In patients with difficult neck anatomy, it may be impossible to identify the landmarks for percutaneous superior laryngeal nerve block. Recently, some authors have published isolated case reports where ultrasound-guided superior laryngeal nerve block was attempted. However, ultrasound visualization of the superior laryngeal nerve was not always possible and ultrasound was essentially used to place local anesthetic in the approximate vicinity of the superior laryngeal nerve near the hyoid bone or perform a translaryngeal instillation of local anesthetic.7–9 In cadavers, it is possible to simulate ultrasound-guided superior laryngeal nerve blockade and demonstrate dye placement around the nerve by placing the injectate either near the hyoid bone or directly onto the nerve.8–10 Consistent sonographic visualization of the superior laryngeal nerve in patients however continues to be a challenge.11
This case series demonstrated that effective ultrasound-guided superior laryngeal nerve block can be achieved in patients who require awake fiberoptic intubation. Until recently, ultrasonographic visualization of the superior laryngeal nerve has not been possible due to its small size (1 mm diameter in most cases) and the limited resolution capabilities of most ultrasound imaging systems.10–12 Relatively new improvements in ultrasound imaging technology have resulted in commercially available ultrasound probes that offer higher resolution.
Before advocating an ultrasound-guided technique for superior laryngeal nerve block, it is necessary to demonstrate that the nerve and surrounding structures can be visualized in a systematic approach that is reliable, reproducible, and consistent with the known anatomy of the superior laryngeal nerve space. Barberet et al.10 used a 12-MHz probe to demonstrate that it was possible to scan the superior laryngeal nerve space but not the superior laryngeal nerve in cadavers and 100 patients. They were able to visualize the thyroid cartilage and hyoid bone with the probe in a parasagittal plane. When the probe was moved laterally, they were able to visualize: (1) thyrohyoid muscle (large hypoechoic band, inserted on the hyoid bone and passing over the thyroid cartilage); (2) thyrohyoid membrane (hyperechoic layer, marking the interface with the hypoechoic pre-epiglottis space); and (3) the interface between the luminal surface and the superficial mucosae of the larynx (hyperechoic layer). The superior laryngeal nerve was not visualized in any patient, and the superior laryngeal artery was seen in 1 of 100 patients. Because of these findings, they were only able to speculate on the theoretical possibility of ultrasound-guided superior laryngeal nerve block. In volunteers and cadavers, a technique for ultrasonographic visualization and injection of the superior laryngeal nerve has been described.1,2 A small hockey stick-shaped 8 to 15 MHz transducer was used to visualize the superior laryngeal nerve. Because of the smaller transducer size, it was easier to place the transducer in a sagittal position to obtain a good image of the hyoid and manipulate it from both the transverse to longitudinal planes without image compromise. Subsequently, the transducer was rotated obliquely to obtain a consistent ultrasonographic image of the superior laryngeal nerve as it travels medially and caudally toward the thyrohyoid membrane. To confirm the identity of the structure, the ultrasound image was examined for a fascicular appearance of nerve tissue, and the nerve was traced to where it pierced the thyrohyoid membrane. Visualization of the superior laryngeal artery was inconsistent and difficult, despite an earlier case report suggesting the use of this landmark in finding the superior laryngeal nerve.8 The hyoid bone, thyrohyoid cartilage, thyrohyoid membrane, and superior laryngeal nerve were visible in 40/40 scans (95% confidence interval, 0.896–1.0).2
In this case series, we were able to obtain consistent reliable images of the superior laryngeal nerve as a hypoechoic structure and trace it as it perforated the thyrohyoid membrane. Accidental puncture of surrounding anatomical structures did not occur, and superior laryngeal nerve block onset occurred in a timely fashion. The superior laryngeal nerve block was accomplished easily within 10 minutes in all cases, and the patients tolerated awake endotracheal intubation with no evidence of incomplete anesthesia in the distribution of the superior laryngeal nerve.
In conclusion, (1) improvements in ultrasound technology have made it possible to obtain high-resolution images of the superior laryngeal nerve; (2) in-plane needle advancement toward the superior laryngeal nerve followed by circumferential placement of local anesthetic is possible with ultrasound; (3) reliable blockade of the superior laryngeal nerve can be expected with this technique. No adverse effects related to superior laryngeal nerve block were observed in any patient.
We believe that anesthesiologists should be aware of the use of ultrasound-guided superior laryngeal nerve block because topical local anesthesia of the upper airway may not be possible in all cases where awake fiberoptic intubation is indicated (severe swelling of tongue, inability to open mouth, etc.), and this approach should be considered when patient anatomy makes a blind percutaneous approach technically challenging.
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