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EMG OF INTRINSIC LARYNGEAL MUSCLES • • • • • Electrodes Bipolar hooked wire electrodes, 75 µm diameter bifilar stainless steel wires (preferred for purely diagnostic work) Bipolar concentric needle electrode Unipolar wire electrode Unipolar needle electrode Unipolar injection needle electrode EMG OF INTRINSIC LARYNGEAL MUSCLES • No sedation necessary • Oxygen by nasal cannula available • 1% lidocaine with 1:100,000 epinephrine for injection with 27gauge needle • Equipment for and personnel experienced in airway management readily available (crash cart, 14gauge angiocatheter, trach set) EMG OF INTRINSIC LARYNGEAL MUSCLES • Elevate back to near 90 degrees if necessary to improve videolaryngoscopy (most can be done with patient supine) • Necessary to extend neck for exposure and placement of needles • Inject 0.5 cc lidocaine 1% with 1:100,000 epinephrine superficially in small weal over midline cricothyroid ligament (for thyroarytenoid recording) and 1 cm inferiorly over lower border of cricoid (for CT recording). EMG OF INTRINSIC LARYNGEAL MUSCLES Palpate structures of anterior neck to definitively identify midline, cricoid cartilage, lower border of thyroid cartilage, thyroid notch, and hyoid bone. Difficult in obese patients Avoid excessive injection of local anesthetic to allow continued palpation of structures after injection. If tracheotomy is present, it is usually necessary to remove it for access for needle placement. Perform only on patients able to tolerate short-term removal of tracheotomy tube. May use nasal speculum placed into tracheotomy site to maintain airway during testing EMG OF INTRINSIC LARYNGEAL MUSCLES Cricothyroid muscle Pierce the skin in midline with electrode and direct needle posterolaterally along long axis of pars oblique aiming at lower surface of thyroid cartilage posterior to the inferior tuberculum without penetrating cricothyroid ligament . a.Too superficial: sternohyoid b.Too deep: lateral cricoarytenoid EMG OF INTRINSIC LARYNGEAL MUSCLES Cricothyroid muscle Confirm placement with maneuvers a.Cricothyroid: activity varies responsively with diminished activity with phonation at low pitch and increased activity at high pitch b.Sternohyoid: activity with elevation of head (glottis open to keep LCA activity silent) c.Lateral cricoarytenoid: burst of activity associated with initiation of phonation EMG OF INTRINSIC LARYNGEAL MUSCLES Thyroarytenoid muscle Pierce skin in midline with electrode directed superolaterally through cricothyroid ligament to depth (from skin) of 1.5 to 4 cm depending on thickness of neck and angle of entry. After needle pierces skin, TA should be entered through a submucosal approach without entering airway. Too superficial: sternohyoid or cricothyroid Too deep: through vocal fold into posterior cricoarytenoid Too medial: enter laryngeal lumen with EMG recording "air" (60 cycle burst of noise) EMG OF INTRINSIC LARYNGEAL MUSCLES Thyroarytenoid muscle Confirm placement with maneuvers a.Marked thyroarytenoid activity with breath holding, glottal stop, and phonation b.Position of needle electrode may be confirmed by moving electrode within substance of thyroarytenoid muscle and observing vocal fold movement with fiberoptic scope. May cause patient to swallow or cough.
