Objective: To quantitate bupivacaine concentration and formulation effects on chondrocyte viability in vitro. Study design: Controlled laboratory study. Sample population: Primary canine chondrocyte isolates. Methods: Cell passage 3 and 4 canine chondrocytes were exposed to 0.9% saline; canine chondrocyte growth medium; 0.4, 0.5, 0.6, 1.5, 2.5, 3.5, or 5 mg/ mL preservative-free standard formulation bupivacaine (SFB); or 13.3 or 6.65 mg/mL liposomal encapsulated bupivacaine (LEB) for 1 hour. Chondrocyte viability and clonogenicity were quantitated with 3-(4,5-dimethylthiazol-2-31 yl)-2,5-diphenyltetrazolium bromide (MTT) and clonogenic assays, respectively. Differences among concentrations and formulations were assessed with Kruskal-Wallis and Dwass-Steel-Critchlow-Fligner post hoc tests. Results: Growth medium had the highest cell viability based on MTT metabolism. Similarly, all LEB concentration groups had higher cell viability compared with SFB concentration cells treated with 3.5 or 5 mg/mL SFB (P < .03). Among SFB concentrations, cell viability was higher at 0.6 mg/mL compared with at 2.5 mg/mL or greater (P < .03). Cell clonogenicity was not significantly different between saline, culture medium, or 0.5 mg/mL SFB. Clonogenicity was lower with all tested LEB concentrations compared with saline or medium (P < .02). Conclusion: In vitro toxicity of SFB on canine chondrocytes is concentration dependent. Liposomal encapsulated bupivacaine may have time-dependent effects resulting in chondrotoxicity. Clinical significance: Clinically relevant concentrations of SFB after a single injection may not result in chondrotoxic effects in vitro. Liposomal encapsulated bupivacaine should not be used in the articular environment.

Objective: To describe the morphology of the lymphatics in the region of the cisterna chyli in healthy dogs and in dogs with idiopathic chylothorax by using computed tomographic lymphangiography. Study Design: Retrospective study. Animals: Nine dogs with idiopathic chylothorax and six healthy dogs. Methods: Computed tomographic lymphangiograms were reviewed to evaluate the number of cisterna chyli branches, total cross-sectional area of the branches normalized to the cross-sectional area of the aorta, number of branches with cross-sectional area greater than 25% of the aorta cross-sectional area, and ratio of the total perimeter to the total cross-sectional area of the branches. Data (mean ± SD) were compared between unaffected dogs and dogs with idiopathic chylothorax. Results: The cisterna chyli included more branches in dogs with chylothorax (4.30 ± 1.57) than in unaffected dogs (1.67 ± 0.56, P = .02), occupying a relative perimeter approximately double that in unaffected dogs (P < .001). The relative cross-sectional area of the cisterna chyli was approximately twofold smaller in affected (0.73 ± 0.35) than in unaffected (1.63 ± 0.91, P = .02) dogs. The fraction of dogs with branches greater than 25% of the cross-sectional area of the aorta tended to be larger in unaffected dogs (P = .07). Most larger branches were located dorsal or to the right of the aorta. Conclusion: The cisterna chyli of dogs with idiopathic chylothorax contained smaller and more numerous branches compared with that of unaffected dogs. Clinical significance: Altered cisterna chyli morphology may impact the surgical approach for cisterna chyli ablation in dogs with idiopathic chylothorax. 1 | INTRODUCTION Chylothorax is the accumulation of chyle in the pleural space, which can result in respiratory distress, malnutrition, and chronically restrictive pleuritis. 1,2 Causes of chylothorax include trauma, cardiac disease, cranial mediastinal masses, heartworm disease, fungal granulomas, cranial vena caval thrombosis, and congenital abnormalities. 1,2 When an underlying cause for the accumulation of chyle cannot be found, the disease is considered idiopathic. Medical management of idiopathic chylothorax in dogs is rarely successful. Thoracic duct ligation (TDL)