A new application for superior laryngeal nerve block: transesophageal echocardiography

Superior laryngeal nerve block: an anatomical study comparing two techniques

STUDY OBJECTIVE

To determine whether an anterior approach is as successful as the conventional posterior approach to superior laryngeal nerve block.

DESIGN

Prospective observational study.

SETTING

University anatomy laboratory.

PATIENTS

20 formalin-fixed adult human cadavers.

MEASUREMENTS

Simulated superior laryngeal nerve blocks were performed by a single operator using 3 mL of 0.01% analine blue dye with a 23-gauge Quincke tip needle. Two different landmark techniques were used on each undissected cadaver: 1) the conventional posterior approach using the hyoid bone as a palpable landmark, with injection at the posterior third of the thyrohyoid membrane; and 2) the anterior approach, using the anterior thyroid notch of the thyroid cartilage, with injection at the anterior third of the thyrohyoid membrane. The spread of analine dye was observed. An injection was deemed successful if the entire paraglottic space was stained or the superior laryngeal nerve stained as it entered the paraglottic space.

MAIN RESULTS

Both techniques were equally successful after 40 injections.

CONCLUSION

There was no significant difference in success in staining the superior laryngeal nerve in human cadavers between the conventional posterior approach and an anterior approach.

Novel intubation technique for transesophageal echocardiographic examination

Pharyngeal intubation is a challenging problem during transesophageal procedures. The rate of unsuccessful intubation varies from 1.5 to 1.9%. In this article, we described a novel technique, which we utilize in our hospital for the difficult intubations without any technical failure for the insertion of the transesophageal probe.

Anatomical study applied to anesthetic block technique of the superior laryngeal nerve

BACKGROUND

The topography of the internal branch of the superior laryngeal nerve (ibSLN) was prospectively studied to evaluate the greater horn of the hyoid bone (ghHB) and the incisura of the thyroid cartilage (iTC) as anatomical repairs in laryngeal anesthetic block. Factors such as gender, ethnicity and side of the neck were also analyzed concerning their influence in the ibSLN position.

METHODS

One hundred neck dissections were performed in 50 human cadavers bilaterally identifying the ibSLN, the ghHB and iTC. The distance between the ghHB and ibSLN in the cranio-caudal direction (dHB), and the distance between the iTC and the ipsilateral thyrohyoid membrane ostium (dTC) were measured. Furthermore, the results were statistically analyzed according to ethnicity, gender and side of the neck.

RESULTS

The ibSLN was juxtaposed to the apex ghBH in 31 out of 100 dissections. The mean dHB was 2.4 mm, and mean dTC was 33.4 mm. The statistical analysis did not identify any significant difference regarding those distances between the groups in terms of ethnicity, gender and side of the neck.

CONCLUSION

The ibSLN was often dissected very close to the ghHB, and this result was not influenced by any factor studied. Therefore, the ghHB can be considered a good anatomical repair to localize the ibSLN in the local block of the larynx. Furthermore, the dTC could frequently be reached by routinely used nerve block needle. However, a few anatomical variations may occur, resulting in a low failure rate of this anesthetic procedure.

Superior laryngeal nerve block: an anatomical study

Superior laryngeal nerve anaesthesia is frequently used to facilitate endotracheal intubation in the awake patient. We have modified the transcutaneous approach to this nerve block to employ a short bevel needle. This improves tactile perception in performing the procedure thus simplifying identification of the correct depth of injection. This study was designed to determine the anatomical basis of superior laryngeal nerve anaesthesia and to estimate the success rate using our modified technique. At autopsy, 20 cadavers had nerve block performed substituting 0.02% methylene blue for local anaesthetic. Dissection was then performed to identify the anatomical structures stained by the simulated local anaesthetic. Additional dissections were performed in formalin-fixed cadavers. We found that the dye was injected into the paraglottic space bounded laterally by the thyrohyoid membrane and thyroid cartilage, medially by the laryngeal submucosa, caudad by the conus elasticus, cephalad by the hyoid bone, and anteriorly and posteriorly by the anterior and posterior thyrohyoid ligaments, respectively. The internal laryngeal nerve, the sensory branch of the superior laryngeal nerve, passed through this compartment and was heavily stained with simulated local anaesthetic. Resistance to the passage of the short bevel needle was provided by the lateral glossoepiglottic fold, not the thyrohyoid membrane as we had expected. Of 40 injections, 39 were deemed successful for a success rate of 97.5%. We conclude that this is a simple and highly successful technique for performing superior laryngeal nerve anaesthesia.

Sensory blockade for difficult passage of transesophageal echocardiography probes

During transesophageal echocardiography probe passage, airway reflexes are usually obtunded with topical local anesthetics. This technique meets with varying degrees of success. Even partially intact airway reflexes result in coughing, retching, and withdrawal, which may prevent transesophageal echocardiography examination or predispose to life-threatening tachycardia and hypertension. Proper preparation of the patient enhances comfort and helps protect against tachycardia and hypertension as well as reducing the time required for examination. This article outlines specific monitoring issues and offers precautions that are critical to transesophageal echocardiography probe passage. It suggests a premedication regimen and describes methods of sedation. Furthermore, it outlines the afferent innervation of the upper airway and specific techniques of temporary reflex interruption.