Exercise intolerance in the equine athlete, due to a functional mechanical abnormality (functional pharyngeal obstruction), has been well documented in recent years. One of the causative factors, dorsal displacement of the soft palate (DDSP), is a condition being diagnosed with increasing frequency.

Causes of DDSP are numerous and have been well documented in the literature. Factors involved in DDSP are:

1. Elongated soft palate.
2. Excessively thin soft palate.
3. Shortened (6-7 cm) or flaccid epiglottis.
4. Excessive retraction of the tongue over the bit.
5. Over-flexion of the poll.
6. Paresis of the soft palate due to deficits of cranial nerves IX and X.
7. Excessive retraction of the larynx by the stemothryolyoideus muscle.
8. Palatal myositis.

Traditional surgical correction has included soft palate resection (staphylectomy) myectomy of the stemothyrolyoideus, and splitting of the soft palate with a sharp metal hooked instrument. The objective of this article is to introduce a new surgical technique, using an electrosurgical instrument to incise the soft palate.

Most cases are asymptomatic until the rate and intensity of exercise causes respiratory distress. In all horses affected with intermittent or exercise-induced DDSP, there is an observed inability to sustain speed workouts. Affected animals appear clinically normal at rest and after light exercise.

Abnormal respiratory noises (gurgling sounds) are usually present in animals with DDSP, but because the noise may cease with deglutition, or as the respiratory rate returns to normal, detection of such sounds by the jockey during a race or close observation immediately thereafter is required. Most horses can be observed making inspiratory and mainly expiratory noise while stressed, which corrects rapidly once the horse ceases exercise. If respiratory noises are present, signs of mouth breathing may also be observed. Even though respiratory noises by be present for only a short time following exercise, my experience indicated that DDSP will continue until tidal volume, respiratory rate, and intensity return to near normal values. For these reasons, and endoscopic examination should be performed as soon after exercise as possible to ensure a more accurate evaluation. Any DDSP observed at this time should be considered significant, provided the history and clinical signs are consistent. The increased use of high-speed treadmills will be very helpful in diagnosis and observing the dynamics of DDSP and other upper respiratory abnormalities.

Horses with DDSP appear to have an increased incidence of bronchitis. This bronchitis may be caused by aspiration of saliva and food material into the trachea when DDSP occurs. The presence of saliva and/or food particles in the trachea after exercise strongly indicates exercise- induced DDSP, even if a post exercise indoscopic examination reveals no abnormalities. Many animals exhibit a cough after exercise to clear the trachea or replace the soft palate (similar to a horse with pulmonary hemorrhage).

It has been reported that a large number of horses also have a concurrent lymphoid hyperplasia. This could be due to the soft palate movement when displacement occurs. Bronchitis and lymphoid hyperplasia have been proven to affect performance in the same way DDSP does. But if these conditions are non-responsive to therapy, or recur after therapy, an underlying cause may be present.

A new technique for correction of DDSP is accomplished by splitting the soft palate using a specifically designed electrosurgical instrument, the Vetroson Soft Palate Resector. The Vetroson Resector is 36” long and curved slightly to conform to the nasopharynx of the horse. The distal end has a tip, which is formed in a semicircular curvature, through which a 1” wire cutting electrode is positioned. The tip easily hooks over the soft palate. The handle on the resector has a 6’ (cable) wire, which plugged into the surgery jack of the Vetroson Macan Electrosurgy Unit (MVS).

The horse is given a preoperative dose of .12mg/lb of acepromazine and .01mg/lb of xylazine, induced with 5% guaifenesin (Gecolate: Summit Hill Laboratories) and 3 g of Thiarrylal Sodium (Biotal: Bioceutic) and is maintained on this mixture. This anesthetic regime is used due to the shortness of the procedure and to control deglutition, which is difficult with a xylazine/ketamine mixture. After induction, the horse is place in lateral recumbence.

A fiber-optic endoscope is passed through one nasal passage to the area of the larynx, while the instrument is passed through the opposite nasal passage and manipulated to hook the soft palate in the center. If the soft palate is not displaced at this time, it can be easily displaced with an endotracheal tube. The resector is hooked over the edge of the soft palate. Using the surgery mode of the Vetroson Macan Electrosurgical unit, the soft palate is then cut anteriorly ½ cm to 1 cm in front of the tip of the epiglottis. Since hemorrhage is controlled, the surgery site is easily visualized making the amount of soft palate being incised accurately controlled. The procedure takes approximately 10 to 15 minutes.

Postoperative treatment includes placing the animal on 1 mg/kg phenylbutazone intravenously for three days to decrease the inflammation. The horse is walked for the same three days and normal training is resumed after this time. Two weeks post surgery, the animal is re-examined by endoscope to evaluate healing. This examination should show the soft palate healed and retracted to form a “V” with no ingesta in the nasopharynx area. Continued use of a tongue-tie when normal training is resumed is advised in all cases.

This procedure has been used on 32 horses over the last 3 years. Our results have been very favorable, with our success rates going as good as any other published report with a much quicker return to training. No post-operative complications were observed in any of the cases.

With our success rate, rapid return to training and the decreased incidence of complications, should all be factors that favor the use of this particular procedure when considering surgical intervention for DDSP.

Although general anesthesia is recommended for this procedure, the following advantages outweigh the risks involved, because.

1. Improved and continuos visualization.
2. Control of the amount of soft palate incised.
3. Decreased and controlled hemorrhage.
4. Shortness of the procedure.
5. Safety to the animal and personnel.

Three of the aforementioned cases involved horses with a smaller than normal epiglottis. Clinical diagnosis was made by endoscopic visualization of the epiglottis per os. These horses returned to training without complications, and were successful.

The electrosurgical instrument has also been used on three cases of epiglottic entrapment, with good results.

The use of the Soft Palate Resector is effective for epiglottic entrapment by incising the arytenoepiglottic folds when adhesion has not developed. More cases are needed to determine its effectiveness on individuals in which adhesion has developed.