FRANK J. MILNE STATE-OF-THE-ART LECTURE Table 3. Classification of Postoperative Abduction After Laryngoplasty


Laryngeal Grade


1 2 3


4 5


Description Maximal or supramaximal abduction


Targeted degree of abduction 75–90% of maximal abduction


Slight above neutral resting position Paramedian position of the arytenoid Midline position of the arytenoid


Modified from Dixon et al.75 Comments


The junction of medial aspect of the left and right corniculate process is no longer on the midline


Abduction between grade 2 and 3


Some curving of the arytenoid cartilage is present indicating abduction Below neutral resting position, i.e., postinhalation No detectable abduction


and thus proper epiglottic retroversion to pro- tect the trachea (these horses are more likely to respond to laryngeal tie-forward in our experience)


3. Esophageal regurgitation (because of damage to the cranial-esophageal sphincter or fibrosis involving the esophagus causing a simple obstruction)


The goal of endoscopy during swallowing is to identify the mechanism or site of respiratory in- tegrity incompetence. These sites are defined as either oropharyngeal-to-nasopharyngeal aspira- tion, oropharyngeal-to-tracheal, and upper esoph- ageal regurgitation.73 This is an emerging field for surgeons and has been observed with and with- out any prior surgical intervention.77,78 Barium swallows are of value in identifying those yet they are less readily available so the endoscopic swal- lowing test is used more often. Typically, the horse is fasted overnight to en-


sure a good appetite. The endoscope is placed through the right nasal passage and secured to the horse halter as performed for treadmill endoscopy (alternatively, an overground endoscope can be used). The horse or foal is then fed at the height at which the aspiration or coughing is reported. In foals, the endoscopy is performed while it nurses on the mare as that is when the aspiration is most common. In adult horses, it is at shoulder height. During barium studies, the horse forms a bolus in the caudal aspect of the nasopharynx, caudal to the base of the tongue which is detected by elevation of the caudal aspect of the soft palate. During swallowing, this bolus is elevated over the closed larynx (by the combination of laryngeal el- evation and epiglottic retroversion, adduction of the vocal folds and arytenoid cartilages with the lateral aspect of the larynx being sealed by the ary-epiglottic folds). The above three sites of la- ryngeal competency can then be evaluated as well as the three mechanisms of laryngeal closure. In severely dysphagic cases, only one or two swal- lows can be observed given that after contamina- tion assessment of its source may be prevented. In addition to looking for the site of the feed pen-


etration, one should confirm and evaluate the fol- lowing critical sites:


1. Verify that the epiglottis is indeed retrovert- ing properly. This is determined by observ- ing the epiglottis fully covering symmetrically the arytenoid cartilage and “coming back down” at the end of the swallowing phase as the nasopharyngeal constriction is released


2. Proper midline contact of the vocal fold and arytenoid cartilage (Fig. 5, A–C) is occurring 3. Esophageal reflux is not occurring (Fig. 6)


Dynamic Endoscopy Fixed airway obstruction resulting in resistive breathing can generally be identified by external examination of the upper airway and by resting endoscopy. Many obstructions occur only or more markedly during exercise because of one or more of the following: increased respiratory pressures, in- creased respiratory frequency, and decrease inspira- tory and expiratory times associated with exercise.1,65,79,80 The reduction in airway geometry results in changes in kinetic energy, velocity, and turbulence in the airway5,81 which results in second- ary collapses. Therefore, an airway obstruction may change airflow pattern and wall-pressures and explain why secondary collapse may also be observed and have been reported in nearly 50% of horses. Dynamic endoscopy is an important diagnostic test


to allow recognition of dynamic collapse or to confirm the absence of airway obstruction.82 Dynamic endos- copy during exercise was first performed using stan- dard flexible videoendoscopes with horses exercising on a high-speed treadmill (HSTE) (HST). This form of dynamic endoscopy was first popularized by clinicians at Tufts University in the 1980s.86 Many other equine clinicians40,42,84–86 have per- formed those dynamic exams as it became the gold standard for the diagnosis of upper airway abnormal- ities in horses. It remained the gold standard proba- bly until a few years after the introduction of commercially available overground endoscopes (OGEs).87,88 The advantages of HSTE are that the protocols are well established leading to a maximal or near-maximal exercise intensity.4,40,42,83,85,89–95 In


AAEP PROCEEDINGS  Vol. 62  2016 91


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