Indirect Laryngoscopy Rationale

Visualization of the glottis by indirect laryngoscopy can confirm vocal cord paralysis resulting from the loss of intrinsic laryngeal muscle innervation. All the intrinsic laryngeal muscles, except the cricothyroid, are innervated by the recurrent laryngeal nerve. Loss of motor innervation from the recurrent laryngeal nerve, as may occur secondary to a mediastinal tumor or as a complication of thyroidectomy, results in vocal cord paralysis and hoarseness. With bilateral vocal cord paralysis, the cords are positioned close to the midline and show no abduction during inspiration. Audible stridor is almost invariably present. Stridor also occurs during the laryngospasm and/or laryngoedema that can be encountered immediately after removal of an endotracheal tube.

Methodology

Indirect laryngoscopy is performed in the awake patient by advancing a small angled mirror through the open mouth to the soft palate while protruding the subject's tongue. Illumination of the angled reflecting surface allows visualization of the glottic aperture through the oral cavity. Topical anesthesia of the soft palate can help minimize the gag reflex. As the cords are being visualized, the patient is instructed to vocalize an "e" sound that normally adducts the vocal cords. Failure of one cord to adduct indicates ipsilateral vocal cord paralysis. In the case of bilateral vocal cord paralysis, both cords are close to the midline and show no abduction during inspiration and may even show paradoxical movement with respiration due to the effects of changes in in-tralumenal pressure on inspiration and expiration. Direct laryn-goscopy is performed under general anesthesia. With the advent of fiberoptic scopes, this latter technique is rarely indicated in adults to assess the presence or absence of vocal cord paralysis.

Advantages

Indirect laryngoscopy is an easy technique that requires little equipment. It is performed in awake patients. It provides a direct visual assessment of vocal cord movement and is the technique of choice for confirmation of vocal cord paralysis if a fiberoptic instrument is not available.

Disadvantages

As a visual assessment of intrinsic laryngeal muscle activity, indirect laryngoscopy is limited to determining the presence or absence of motor innervation. Bilateral but asymmetrical movement of the vocal cords is difficult to quantify. This finding may suggest vocal cord paresis but can also arise from other conditions.

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