Prospective clinical trial of cats undergoing thoracoscopic thoracic duct ligation for idiopathic chylothorax

Currently, there are no prospective studies for cats with idiopathic chylothorax using standardized preoperative diagnostics and surgical techniques for each patient. This includes the use of contrast material before and during surgery to better identify the thoracic duct and stop its flow at the proper location, which is highly dependent on each cat. The aim of this project is to assess the outcome of cats with idiopathic chylothorax undergoing thoracoscopic thoracic duct ligation who have a standardized diagnostic workup preoperatively and successful preoperative and intraoperative thoracic duct visualization.

Enrollment Status: Currently Enrolling

Inclusion criteria: Cats are invited to participate in this study because if they are at least 6.6 lbs (3 kg) or greater, greater than 2 years of age, and have been diagnosed with idiopathic chylothorax.
Prior to inclusion into this study cats will undergo physical examination and be diagnosed with chylothorax using pleural effusion fluid analysis (abnormal buildup of fluid in the pleural space, which is a thin cavity between the lungs and the chest wall). If not already completed within two weeks of their planned surgery date, cats will undergo a complete physical examination, and blood will be collected for complete blood count and serum biochemistry prior to admittance in this study. Additionally, cats will receive a complete work-up for chylothorax including an echocardiogram (heart ultrasound), heart worm testing, chest x-rays,
and pleural effusion fluid analysis.

Exclusion criteria: If a cat has undergone surgery previously for chylothorax or if they have an identified underlying cause of chylothorax (e.g. cancer, heart disease, lung lobe torsion, etc.), they will be excluded from participation in this study.

Treatment: All cats with undergo preoperative diagnostic testing including pleural effusion analysis, bloodwork, and echocardiogram. Cats will be placed under general anesthesia for their first procedure. A CT scan will be conducted first, where a contrast solution (iohexol) will be injected underneath the skin around the anus and/or into the metatarsal paw pads, to highlight the thoracic duct. Under the same anesthetic event, your cat will also have a small incision made into its neck and a catheter will be placed in the jugular vein to measure pressures at the level of the heart. At a later date, your cat will be placed under anesthesia again for surgery. Three very small (5-10mm) incisions will be made near the ribs for insertion of special surgical instruments (thoracoscopic camera and instruments) to allow the surgeon to see inside the chest cavity and close the thoracic duct branches. The thoracic duct will be visualized using a dye injected around the anus prior to surgery. If the thoracic duct is unable to be visualized with this minimally invasive technique, an incision will be made into the chest cavity between two of the ribs and the surgery will proceed as an “open” thoracic duct ligation. A chest tube will be placed to monitor post-operative fluid production in all patients, as is standard of care for chylothorax patients. All enrolled cats will be hospitalized post-operatively in the intensive care unit for a minimum of 48 hours for monitoring. The chest tube will remain in place for a minimum of 48 hours, and post-operative fluid analysis and triglyceride levels will be measured at 24 and 48 hours post-operatively. Your cat will be sent home once they are voluntarily eating and drinking, and their pain is deemed appropriately controlled with oral medications. As part of your agreement to enter this study, all cats must be re-evaluated at the UF Small Animal Hospital at 1-, 3-, and 6 months after surgery for physical exam and chest x-rays to confirm occlusion of the thoracic duct and resolution of chylothorax. A repeat CT scan under anesthesia will be performed at 3 months post-surgery, or sooner if clinical signs reoccur before then.

Cost: This study will cover a maximum of $1000 towards the cost of anesthesia, surgical procedures, and any required medications and hospitalization incurred during the initial
CT and the surgery. The study will also cover the cost of jugular vein catheterization procedure performed during the first anesthesia as well as the repeat CT scan (and associated anesthetic costs) performed 3 months after the initial surgery (or sooner if clinically indicated). No other costs will be covered by the study. You will be responsible for all fees associated with follow-up, as is standard for chylothorax patients

PIs: J Brad Case: (352-214-1051) caseb@ufl.edu, Camille Andrews: camilleandrews@ufl.edu

Background information:

Some cats are at risk of developing a condition called chylothorax. Chylothorax can occur because of a “leaky vessel” (known as the thoracic duct), which can cause accumulation of fluid (chyle) in the chest cavity. This excess of fluid within the chest cavity can impair the lungs during breathing and result in potentially life-threatening situations. Treatment of chylothorax in cats typically requires surgery to close the thoracic duct, preventing fluid from leaking into the chest cavity. Traditionally, surgical intervention of chylothorax requires opening the abdominal and chest cavities, causing a considerable amount of discomfort and even pain after surgery. Minimally invasive approaches have been developed, like thoracoscopic thoracic duct ligation where closure is performed through small incisions with the use of a camera and specialized instruments. The addition of another technique, known as pericardiectomy (removal of the pericardium, which is a sac-like organ surrounding the heart) along with thoracic duct repair is often performed to reduce the chance of recurrence. Even with these techniques in combination, recurrence rates of up to 30-50% have been reported. Additionally, more recent studies suggest that pericardiectomy may not be necessary in all patients, but rather proper identification of the location of the thoracic duct before surgery by way of a CT scan and in surgery by way of contrast can improve outcomes for cats.