Chylothorax Trial

Clinical Trial for the Treatment of Chylothorax in the Dog

Home

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

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

What new treatments are to be studied in this clinical trial?

The recent introduction of two new procedures, cisterna chyli ablation with thoracic duct ligation (CCA-TDL) and pericardectomy with thoracic duct ligation (P-TDL), mark the introduction of two new conceptual approaches to the treatment of chylothorax. CCA-TDL focuses on creating an environment conducive to the formation of lymphatic drainage channels to the venous circulation outside of the pleural space. Thus, this approach utilizes the strategy of shunting chyle to the venous system without transport via the thoracic duct with its attendant risk of bypass of the duct ligature and recurrence of the chylothorax. The destruction of the cisterna chyli does two things; first, it prevents the lymphatic hypertension that occurs with thoracic duct ligation. Evidence of this hypertension can be clearly seen in the distension of the cisterna chyli after thoracic duct ligation. Experimental studies have shown that new lymphaticovenous channels require 5 to 14 days to form. Thus, alleviation of lymphatic hypertension will prevent the formation of lymphangiectasis and collateral lymphatic channels and tilt the balance in favor of successfully forming new channels into the venous circulation rather than developing lymphatics that bypass the thoracic duct ligature. The second effect of CCA is to disrupt the connection of the abdominal lymphatics that carry chyle from the thoracic duct. The effect of this is to stimulate these lymphatic channels to find new lymphaticovenous connections in the area of their disruption. Thus, with CCA, chyle is diverted directly to the venous circulation in the abdomen which eliminates the potential for leakage into the pleural space.

Pericardectomy-TDL is based on the hypothesis that venous occlusion is responsible for continued chylothorax. This hypothesis is predicated on experimental models where partial occlusion of the cranial vena cava results in chylothorax in 50% or more of experimental animals so treated. The relationship of this model to the spontaneous idiopathic disease is not clear as there are substantial differences in clinical signs and presentation in the experimental animals versus observations made in animals with spontaneous disease. Nonetheless, this model does provide a plausible hypothesis regarding one potential cause of idiopathic chylothorax. The rationale for P-TDL is to reduce either venous or right heart restriction that may be causing subtle venous congestion as a cause of chylothorax. Preliminary clinical experience reported with this procedure suggest that this approach may have merit.

Is there either experimental or clinical evidence that these procedures may be effective?

There is considerable difficulty in modeling chylothorax in the experimental environment. Procedures applied to normal dogs may have little relevance to the spontaneous disease state and thus, although these studies can be valuable and informative, they must always be interpreted with caution when applying the results to animals with the spontaneous disease. Laboratory studies can only take the clinician so far in terms of evaluating a specific treatment for chylothorax. After that point, it becomes necessary to examine the impact of the treatment in a controlled rigorous manner in the patient population that presents with the spontaneous disease.

However, a recent experimental study conducted at the University of Wisconsin has shown that CCA-TDL does result in a diversion of the abdominal lymphatic drainage into the venous circulation within the abdominal cavity and averts drainage of chyle through the thoracic duct in the majority of dogs so treated. This study confirmed the hypothesis that CCA would promote new lymphatic drainage channels and provided us with information which has allowed us to further refine the procedure, changes which may enhance its effectiveness even more. Further, a limited clinical case series in dogs treated with this technique has shown resolution of the chylothorax in the majority of dogs so treated. Pericardectomy-TDL has also recently been presented as being effective in dogs with spontaneous idiopathic chylothorax (Dr. T. Fossum, Texas A&M University, clinical case data presented at the American College of Veterinary Surgeons meeting, 2002, San Diego, CA).

The purpose of this sponsored clinical trial is to evaluate each of these procedures to determine if they offer an improvement over the current standard of therapy (thoracic duct ligation alone) and if either procedure may be superior and hence provide a new standard of treatment for chylothorax.