Technician Update

Tie Back or Tie Forward

By Kendra Dostaler, RVT, VTS-EVN

A 4-year-old Standardbred mare was referred by her primary veterinarian to the Purdue University Veterinary Hospital Large Animal Surgical Outpatient Services for surgical correction of a left laryngeal hemiplegia.

The mare was in training and competing as a trotter. The owner and trainer noticed that the mare would have several good races followed by a race in which she would “stall out” around the three-quarter pole. At 1 point during a poor performance race, the trainer was concerned that the mare was going to go down.

The trainer also reported the horse had made some noise while racing, but that the noise was not as loud as a classic laryngeal hemiplegia, or “roarer.” The primary veterinarian performed an endoscopic examination and diagnosed the horse with a grade 3 left laryngeal hemiplegia. The owner also mentioned the primary veterinarian had performed injections into the soft palate that had seemed to help.

On presentation to the outpatient surgical services, the mare appeared bright, alert and responsive. Body weight was 552 kg; body condition score was 6/9. Temperature was 99° F (37.2° C), heart rate was 36
beats/min, and respiratory rate was 16 breaths/min. Physical examination showed no abnormalities. No murmurs were present and the lungs were clear. Mucous membranes were pink and moist; capillary refill time was <2 seconds. Borborygmi was normal in all quadrants.

The mare was placed in the stocks, and a wooden-handled rope twitch was placed on the upper lip. Resting endoscopic examination confirmed grade 3 of 4 left laryngeal hemiplegia. However, the clinician recommended a dynamic endoscopic examination before proceeding to surgery since the mare was having inconsistent poor performance issues, which would be unusual for strictly laryngeal hemiplegia. The client consented to a dynamic endoscopic examination.

Dynamic endoscopy involves a wearable endoscope attached to a halter or bridle that is used while the patient is at work on a high-speed treadmill or in the ring to evaluate the soft palate, epiglottis and arytenoids during intense exercise. At Purdue, a high-speed treadmill is used.

Treadmill Trial
The patient was taken directly to the treadmill to begin the test, and an assistant walked her for a few laps around the room so she could become accustomed to the space. Then, protective bell boots and splint boots were placed on all limbs. A surcingle was placed around the barrel in the same fashion as a saddle, and it was cinched up similarly to a girth on a saddle. As the mare was a trotter rather than a pacer, no additional equipment was needed.

The mare became accustomed to the tack and the treadmill by walking a few more laps around the room and by walking across the stopped treadmill; the mare required little exposure, likely due to her maturity and training. She was placed on the high-speed treadmill with a handler on each side and a secure bar in front. The staff was instructed to avoid walking in front of the treadmill during the test, as this would cause the horse to stop while the treadmill belt was still moving. Before starting the treadmill, an emergency stop line was attached to the surcingle.

A warm-up was initiated at 1.5 m/s for 5 minutes. The treadmill was then sped up to 2.5 m/s, and the mare easily maintained this speed for the remainder of the 10-minute warm-up. To test her fitness level for the examination, the speed was increased to 4.0, 6.0, 8.0, and 10.0 m/s for 2 minutes at each speed. The treadmill incline was also increased to 3°.

The mare tolerated the speed and incline changes with ease. The speed was then decreased to 1.5 m/s for 15 minutes. As a result of the mare’s performance on the treadmill, the dynamic endoscopic examination was scheduled for later that afternoon; it is important to note that most horses require at least 2 training sessions prior to a treadmill trial.

The mare was allowed to rest and recover until late afternoon, when the protective boots and surcingle were placed, and the mare was reintroduced to the treadmill area. Following a short warm-up period at 1.5 m/s and 2.5 m/s, she was removed from the treadmill for placement of the endoscope. A wooden-handle rope twitch was placed, the endoscope was secured to her halter, and appropriate placement and positioning were confirmed on a small tablet screen. A simple heart rate sensor was also placed; no additional monitoring was performed due to the mare’s fitness level.

The mare was placed back on the treadmill for the beginning of the examination. The clinician adjusted the speed and treadmill angle based on the video feed from the endoscope. The video feed was monitored from a starting speed of 4.0 m/s, and the speed and angle were at the clinician’s discretion.

At 10.0 m/s, the mare started to show some difficulty keeping up with the incline. The incline was then decreased to 0°, and the mare was able to trot well at 12.0 m/s. After the examination was completed, she was allowed to cool down at 1.5 m/s for 10 minutes, and then she was moved to the ward area, where full-body cold hosing was performed, followed by another 10-minute walk. After the horse was placed back in the stall, she was given access to electrolyte water in addition to her freshwater supply.

A blood sample obtained immediately after the treadmill trial showed a creatine kinase (CK) level of 154 IU/L, which was within the reference range. After 6 hours, the CK concentration was again within the reference interval at 162 IU/L, indicating that no muscle injury was sustained during the trial.

Results of the dynamic endoscopic examination showed a grade 3A left laryngeal hemiplegia and a dorsally displacing soft palate. The mare had normal and complete abduction of the left arytenoid during exercise, so a tie-back procedure was not warranted.

While a dorsally displaced soft palate was not seen on the resting examination, a billowing of the soft palate was appreciated during exercise. The clinician suspected this was happening frequently in work and was the cause of the “roaring” noise that the trainer had noticed. With these combined results, a laryngeal tie-forward was recommended, and feed was withheld beginning at midnight.

Surgical Intervention
The following morning, a 14-gauge over-the-needle IV catheter was placed in the right jugular vein and secured with 2-0 polypropylene suture on a straight needle.

Physical examination showed no abnormalities, and electrocardiography (ECG) showed a normal sinus rhythm. Packed cell volume (PCV) was 35%, and total protein concentration was 6.4 g/dL, both within the reference ranges. Preoperative IV penicillin G potassium, gentamicin and phenylbutazone were administered.

The mare had a high level of anxiety; IV detomidine was administered, and she was allowed to rest in her stall for 20 minutes. She was then moved to the induction area, and butorphanol and xylazine were administered for further sedation. She was induced with ketamine and diazepam. Endotracheal intubation was achieved with a 26-mm internal diameter endotracheal tube. The mare was maintained under general anesthesia on isoflurane inhalant starting at 5% and titrated down as needed.

She was placed on mechanical ventilation, and monitoring was performed via ECG, end-tidal CO2, pulse oximetry, and invasive blood pressure. An arterial blood gas sample was evaluated once during the procedure and found to be within normal limits.

The mare was hoisted onto the surgical table and placed in dorsal recumbency with the head and neck fully extended. Surgical preparation included clipping the hair along the ventral midline from the intermandibular through the upper one-third of the cervical spine region. A 2-phase preparation of the area was then performed using 2% chlorhexidine scrub and 70% isopropyl alcohol.

The surgeons placed a sterile drape, and an incision with a #10 blade was made from just caudal to the cricoid cartilage to just rostral to the basihyoid bone. The surgeons then dissected through the tissues to gain access to the larynx. A trocar needle was inserted, in turn, through the caudolateral aspect of the thyroid cartilage on the right and left sides. A heavy, non-absorbable suture was passed through the trocar needle in the cartilage and through a 2-hole suture button to distribute the pressure from the suture and to prevent the suture from tearing through the cartilage. Once the suture was in place on the thyroid cartilage, the basihyoid was then accessed.

A wire passer was pushed around the left side of the basihyoid, and the suture was passed through from the right side of the cartilage. The contralateral side was then completed, creating an “X” with the suture. The horse’s nose was then flexed to a 90° angle, and the suture was tied tightly.

After the surgeon was satisfied that the larynx was sufficiently pulled dorsal and cranial to the basihyoid bone, the head was left in a semi-flexed position for closing. All layers were closed in a simple continuous pattern, with 1-0 polyglactin 910 suture used for the 2 muscle layers, 2-0 polyglactin 910 suture for the subcutaneous layer, and 2-0 absorbable monofilament suture for the skin. A simple bandage was placed over the site with a surgical towel and elastic tape. Total anesthesia time was 1 hour and 25 minutes.

The mare was moved to a padded recovery stall, and IV xylazine was administered to aid recovery. Recovery was uneventful, and the mare stood on her own on the first attempt. After recovery, another dose of IV potassium penicillin G was administered approximately 6 hours after the preoperative dose. After the mare was upright, an endoscopic examination was performed to ensure the success of the procedure.

That evening, physical examination showed no abnormalities. A halved dose of phenylbutazone was administered approximately 12 hours after the previous dose. After administration, the IV catheter was removed.

The mare was fed with a hay net to maintain her head and neck in a neutral position while eating; the water bucket was kept elevated.

The following morning, the mare appeared bright, alert and responsive. Physical examination disclosed no abnormalities. Oral phenylbutazone was administered, and she was discharged shortly after with orders to continue oral phenylbutazone every 12 hours for 5 more days.

Exercise restrictions were discussed, and the mare was placed on strict stall rest for 4 weeks, with only hand-walking being permitted. MeV

The Technician’s Role
This case was a good example of the need to work with the case that is in front of you and to follow your instincts, as the mare was referred with 1 diagnosis and a request for a type of procedure that was unnecessary.

For initial consultation and evaluation of the mare, I assisted with placing the mare into the stocks and placed the wooden-handled rope twitch. I also set up the endoscope and assisted with the upper airway endoscopy. Soon after, I helped acquaint the mare with the treadmill area, where I placed the splint and bell boots on all limbs.

Working with a high-speed treadmill is not something many technicians are exposed to during their careers. I assisted the treadmill technician with placing the surcingle and moving the mare through the treadmill training.

Later in the day, I performed the same tasks in preparation for the dynamic endoscopic exam. I ran the treadmill controls for the duration of the warm-up for the exam and prepared the mare for the endoscopy. When the mare was placed back on the treadmill, I ran the treadmill controls during the exam. The speed and angle were changed at the direction of the clinician.

After the exam I replaced the wooden handle rope twitch for removal of the scope. And was involved in her cool down.

The following morning, I placed the jugular IV catheter and gave the pre-operative medications through the catheter. Additionally, I completed the pre-operative EKG. Then, I assisted the anesthesia team with induction of general anesthesia. Our team then hoisted the mare onto the surgical table where I helped with proper positioning.

I ensured the surgical area was clipped with appropriate margins and completed the initial prep phase. Once in the surgical suite, I completed the aseptic prep phase and circulated the sterile procedure. In the last phase of the procedure the surgeon requested the head be moved, at his direction, from flexed back to semi-extended. I performed this task while minding the endotracheal tube and sterile fields.

After the procedure was complete, I assisted with moving the patient and positioning her in a recovery stall.

Teaching Points

• A grade 3 laryngeal hemiplegia is defined as partial paralysis of the arytenoid without normal abduction, but there are 3 varying degrees. Grades 3A, 3B and 3C range from normal with complete abduction during exercise to complete paralysis and collapse of an arytenoid and vocal cord into the airway. A letter designation was not specified at the time of presentation.
• The mare was placed in the stocks with a wooden-handled rope twitch placed on the upper lip. These restraint methods are employed during endoscopy, as sedation is contraindicated because relaxation from sedation can cause alterations in the musculature of the soft palate and larynx.
• Before undergoing a dynamic endoscopic examination, the horse must participate in training sessions to expose the unfamiliar horse to the treadmill, ensuring the safety of both the horse and staff. The horse’s level of endurance and comfort at high speeds on the treadmill can also be evaluated. Fortunately, this mare had already been exposed to a high-speed treadmill at the training facility.
• Creatine kinase is an enzyme detected in the blood that can indicate the presence of muscle injury or disease, and is found often in the highest concentration in skeletal muscle. Plasma levels will peak approximately 6 hours after the muscle injury takes place, so a second sample was collected 6 hours after the treadmill trial.