Clinical Trial for the Treatment of Chylothorax in the Dog


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Introduction to and current treatments for chylothorax in the dog

Rationale and basis for new surgical treatments for chylothorax in the dog

Study Design for Evaluation of Cisterna Chyli Ablation or Pericardectomy for Treatment of Chylothorax

Sample Consent Form for Enrollment in the Trial (pdf)

Current Status of the Trial-Results Update


Study Design for Evaluation of Cisterna Chyli Ablation or Pericardectomy for Treatment of Chylothorax

Overview: The design of this study is to be a prospective randomized clinical trial. Informed client consent is obtained and dogs will randomly be assigned to a treatment group using a computerized random number generator. The treatments to be tested will be 1) CCA-TDL or 2) P-TDL. Follow-up of dogs after surgery will be for 1 year.

Patient selection:

  1. Inclusion criteria for dogs to be entered into this study are:
    1. Dogs of any age or breed diagnosed with chylothorax of two weeks duration or longer as determined by chemistry analysis of the triglyceride and cholesterol content of fluid obtained by thoracocentesis. A chylous effusion will be characterized by a significantly higher triglyceride content and relatively unchanged cholesterol levels compared to these values in serum.
    2. Dogs with no other detectable pathology in the chest with the exception of mild heart disease.
  2. Exclusions will be made if there is:
    1. Any evidence of neoplasia or masses on radiographs or cytology of the chest fluid.
    2. A recent (within 1 month) history of trauma
    3. Heartworm positive
    4. Unexplained abnormalities in serum chemistries (ie. hypercalcemia) that may suggest an occult pathology such as neoplasia.
  3. Patient screening tests will consist of:
    1. CBC and chemistry panel, heart worm test
    2. Chest radiographs after thoracocentesis and drainage of as much fluid as possible from the pleural space. Fluid volumes taken from the chest will be measured.
    3. Fluid analysis for triglycerides and cholesterol and cytology
    4. Echocardiogram
  4. Study size and recruitment: The proposed study will consist of 30 dogs per treatment group. The study will be conducted over 3 years with 10 dogs added to each group per year and then final data analysis done after follow up at 1 year after conclusion of the trial.

Treatment: Surgical treatment will consist of either CCA-TDL or P-TDL. Performance of these procedures will be done by Dr. McAnulty or under the direct supervision of Dr. McAnulty. The surgical procedures are described below.

  1. CCA-TDL: For performance of the CCA-TDL procedure, the basic approaches to the abdomen and the thoracic cavity are the same as for the current standard treatment (TDL alone). In brief, this will require the dogs are anesthetized, clipped and aseptically prepared for surgery. A single surgical field is draped which encompasses the abdominal incision and the right chest for the thoracic incision (there are 2 incisions made for the treatment). The lymphatics are outlined by injection of an abdominal lymph node with new methylene blue dye and by contrast lymphangiogram. The dogs are then rolled into position for the chest incision and the thoracic duct is located and tied off (ligated) using the standard methods. After ligation, a repeat contrast lymphangiogram is performed to confirm complete occlusion of the thoracic duct and all its branches. The cisterna chyli is then removed in the abdominal cavity (this is through the same incision used to perform the lymphatic dye study so no new incision is necessary).

    Postoperative management is done in the Intensive care unit of the UW-VMTH. Intravenous fluids, prophylactic antibiotics, analgesics for pain management and vital sign monitoring are done as per routine for thoracotomy (chest) and laparotomy (abdomen) procedures.

  2. P-TDL: The dogs are anesthetized, clipped and aseptically prepared for surgery as for the standard TDL procedure. An incision is made to expose the lymph node to be injected to outline the lymphatic ducts and complete the lymphangiogram as per the standard treatment. After completion of this study, the chest is entered through a skin incision over the middle of the chest. This incision will be used to allow access to the thoracic duct and access to the pericardium. The thoracic duct is then isolated and ligated as described for CCA-TDL. The pericardium is then removed and the chest closed in a routine manner. Postoperative management is the same as described for CCA-TDL.

Monitoring and follow-up: Initial monitoring after surgery will be done in the ICU. Chest fluid volumes will be recorded as obtained from the chest tubes. Fluid analysis will be done every other day to determine if there are acute changes in the character of the fluid up until the chest tube drain is removed. Following removal of the chest tube, the dogs will be discharged from the hospital. It may be necessary to drain the chest by needle over the next two months since it can take some time for new lymphatic to venous drainage pathways to form. This can be done at the UW-VMTH or at the referring veterinarian. Study follow up will consist of suture removal at two weeks after surgery and then chest radiographs at 1 month, 3 months, 6 months and 1 year after surgery. In cases where clients must travel long distances, radiographs from referring veterinarians will be accepted. In instances where fluid accumulation is detected in the chest by radiographs a sample will be obtained by thoracocentesis for analysis and cytology to determine if it constitutes a continuation of a chylous effusion or if it is non-chylous in nature. Repeat CBC and serum chemistry panels will be performed at the 1 month and 3 month rechecks. Specific outcomes, in addition to analysis of the data that will be accumulated in the medical record during the study period, that will flagged for surveillance will be 1) any respiratory distress after surgery; 2) need for thoracocentesis (needle drainage of the chest) to relieve respiratory distress; 3) presence or absence of a pleural effusion and its composition; 4) surgical complications of any kind.

Review of Results and Continuation of the Trial: The interim results of the trial will be evaluated at the end of each year. The trial will be continued for each group if the incidence of resolution of the chylothorax is 50% or better, an incidence that is indistinguishable from historical results with TDL alone. If the rate of resolution of is less than 50% then that treatment group will be discontinued and all dogs will be enrolled in the other group, presuming that testing of that treatment group is to continue (based on encouraging positive results in that group).



 

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