Veterinary Science Collected Works - Theses

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    Lean body weight adjusted intravenous contrast medium dose for abdominal Computed Tomography in dogs
    Kan, Jennifer Yin Mei ( 2022-01)
    Contrast-enhanced computed tomography (CT) is a common diagnostic modality to investigate abdominal pathology in dogs. For the animal’s safety, the minimum contrast media (CM) dose to achieve diagnostically appropriate contrast enhancement should be administered. Although acute adverse reaction to non-ionic iodinated CM is rare, moderate (>20% from baseline) alteration of heart rate and systemic blood pressure has been reported in dogs. Use of less iodinated contrast is particularly crucial in patients with pre-existing renal dysfunction, as CM is concentrated in renal tubules, having a direct toxic effect, modulating tubular regulatory mechanisms, and producing renal vasoactive substances. Risk of contrast induced nephropathy is considered low in human patients with no history or symptoms of renal disease. In dogs, iodinated contrast dose is commonly linearly increased based on total body weight (TBW). Lean body weight (LBW) has been considered in particularly obese human patients when prescribing a dose of CM, as body fat is not metabolically active and contributes little to dispersing or diluting the CM in the blood. This thesis consists of two published articles (chapter 2 and 4), of which the final research aim was to determine if less iodinated contrast per kilogram TBW can be administered to overweight/obese dogs while maintaining adequate organ and vessel opacification to make a confident radiologic diagnosis. Chapter 2 is a retrospective study performed to determine the variability of major abdominal vessel and organ contrast enhancement and to establish any relationship with abdominal fat percentage in contrast enhanced CT studies, performed on 62 clinical patients at U-Vet Werribee Animal Hospital between February 2014 and February 2019. Intravenous Iohexol (240 or 350 mgI/ml) with a dose range of 660-880 mgI/kg TBW administered by a power injector (1.8 - 3.0 ml/s) and saline chaser was the standard injection protocol used at this institution. Findings based on a linear regression model showed a positive association of aorta (p = 0.005), liver parenchymal (p = 0.045) and portal vein (p = 0.001) enhancement to abdominal fat percentage during the portal venous phase. Following this retrospective study, variability of abdominal organ/vessel contrast enhancement contributed by CM injection method was evaluated and outlined in chapter 3. This was done in attempt to minimise contribution of varied CM injection techniques on organ/vessel contrast enhancement variances prior to the second part of the research project. Out of the three injection techniques explored, the fixed injection duration protocol was found to have the smallest organ and vessel enhancement interquartile range. The fixed injection duration protocol; Iohexol 350 mgI/ml at 700 mgI/kg TBW administration by a cephalic vein intravenous catheter, and a CT study performed with a fixed injection duration of 20 s, with the arterial and portal venous acquisition triggered 10 s and 35 s after aortic arrival respectively, was used for the subsequent part of the research project. Chapter 4 was a prospective study where we hypothesised that LBW adjusted dosing would not affect the diagnostic quality of the abdominal CT study, will minimise negative physiological effects, and reduce variability of contrast enhancement in major abdominal organs and vessels as compared to dosing according to TBW. Results from 12 dogs showed that LBW dosed abdominal CT studies were of diagnostic quality (based on subjective radiologist’s assessment) and reduced inter-individual enhancement (smaller interquartile range) variability in dogs. Contrary to our second hypothesis, there was no significant difference in the change in heart rate and blood pressure after CM administration when dosed according to TBW or LBW. Based on reports in the human literature and findings from the present study, LBW is a better body size index for determining CM dose compared to TBW and is discussed in the final chapter.
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    Evaluation of the analytical performance of a clinical laboratory coagulation analyser for coagulation factor measurement in canine plasma
    Lovatt, Christine ( 2022)
    Abstract Objective: To evaluate the analytical performance of a clinical laboratory coagulation analyser (Stago Compact Max) for coagulation factor activity measurement in canine plasma. Design: Prospective, observational, analytical study. Methods: Whole blood was collected from 15 privately owned dogs aged between 1 and 8 years old. Dobermans and greyhounds were excluded from sample collection. Five dogs (Pool A) over 25kg had up to 175mL of blood drawn from the jugular vein, and this was processed to citrated, platelet free plasma, and combined to provide a sample pool. Ten dogs (Pool B) over 10kg had 20mL of whole blood drawn from the jugular vein, and this was processed to citrated, platelet free plasma and combined to provide a comparison pool. Complete blood count, biochemistry testing and prothrombin (PT) and activated partial thromboplastin time (aPTT) testing was performed on all dogs prior to blood draw. Samples were excluded if they were visually haemolysed, lipaemic or jaundiced. Pool A was used to assess linearity, within-run and between-run precision of fibrinogen, factor II (FII), factor V (FV), factor VII (FVII), factor VIII (FVIII) and factor X (FX). A modified one stage PT assay utilizing human factor deprived plasmas was performed for FII, FV, FVII and FX. A modified aPTT assay utilizing human factor deprived plasma was performed for FVIII. Fibrinogen was measured via the modified clotting method of Clauss. All coagulation testing was performed as per the manufacturer’s guidelines (Diagnostica Stago). Barbitone buffer was used to perform dilutions on aliquots of Pool A, and 7 dilutions were each tested 20 times on the first day of testing to supply data for within-run precision and linearity, and then tested 5 times further for 4 consecutive days to provide data for between-run precision. The following sample: buffer dilutions were tested: undiluted, 9:1, 7:3, 1:1, 3:7, 1:9, 1:19. For coagulation factor activity testing, time to clot formation was measured and interpolated with a standard curve prepared from Pool B plasma. Fibrinogen was interpolated with the calibration curve provided by the manufacturer. Limit of the blank was assessed by performing each coagulation test 5 times with barbitone buffer only. Results: Results were tabulated and mean, standard deviation and coefficient of variation calculated for each factor, for within-run and between-run precision. Concentration vs measured activity were plotted and line of best fit and linear regression analysis performed. Acceptable linearity was determined as an R squared value >0.95. R squared values were as follows: Fibrinogen 0.99, FII 0.99, FV 0.99, FVII 0.99, FVIII 0.99, FX 0.99. Acceptable coefficient of variation was determined based on manufacturer’s data and factor activity levels of importance. Coefficient of variation was above the acceptable range for FV (between-run precision) at an analyte concentration of 5%, FVII (between-run precision) at analyte concentrations of 50%, 30% and 5% and FX (between-run precision) at an analyte concentration of 5%. Relevance: Investigation of coagulation disorders in dogs is a rapidly growing field in veterinary medicine, and the effects of critical illness on coagulation factor activity are poorly understood. Evaluation of the analytical performance of a clinical laboratory coagulation analyser for coagulation factor activity measurement in dogs is the first step in increasing research and clinical assessment in this area.
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    Sensitivity of canine haematological cancers to BH3 mimetics
    Jegatheeson, Selvi ( 2022)
    Background: Haematological cancers such non-Hodgkin lymphoma (NHL) and acute and chronic leukaemias are common in both humans and dogs. Whilst these cancers can be treated with cytotoxic chemotherapy (and immunotherapy in people), development of treatment resistance is common. A frequently identified mechanism associated with resistance to chemotherapy-induced cell death is overexpression of the antiapoptotic B cell lymphoma 2 (BCL2) protein. Highly specific small molecule inhibitors of antiapoptotic BCL2 proteins, known as B cell lymphoma Homology 3 (BH3) mimetics, result in rapid induction of apoptosis in vitro and in vivo in human haematological cancer cells. This has led to the approval of the BCL2-specific inhibitor, venetoclax (VEN), for the treatment of chronic lymphocytic leukaemia (CLL) and acute myeloid leukaemia (AML) in Australia, North America and Europe. Expression of BCL2 has been reported in canine nodal lymphoma, however sensitivity of primary canine cells to BH3 mimetics has not been evaluated. Objectives: This study aimed to assess the in vitro sensitivity of non-neoplastic lymphocytes and primary haematological cancer cells from dogs to VEN or the dual BCL2/BCLxL inhibitor, navitoclax (NAV). The second aim was to evaluate the association between BCL2 protein expression and sensitivity to VEN. Methods: Nine dogs without cancer and 30 dogs with haematological cancers were recruited. Lymphocytes were isolated from peripheral blood, lymph node and/or bone marrow and incubated with VEN or NAV for 24 hours. Viable cells were enumerated using flow cytometry and the half maximal effective concentration (EC50) was calculated; BCL2 protein from whole cell lysates was assessed via immunoblotting. Results: Non-neoplastic lymph node-derived B and T canine lymphocytes were more sensitive to VEN than circulating lymphocytes (P = 0.02). Eighteen dogs with haematological cancers were included in the final analysis, including six cases of non-indolent multicentric B cell lymphoma, four cases of acute leukaemia, three cases of non-indolent multicentric T cell lymphoma, two cases each of indolent T-zone lymphoma and T-cell CLL, and one case of multiple myeloma. Neoplastic T lymphocytes (7/7) showed marked sensitivity to BH3 mimetics, with an EC50 <100nM, whilst 6/7 samples of non-indolent B cell cancers were resistant to VEN, with an EC50 >1000nM. All samples of acute leukaemia showed sensitivity to NAV, however sensitivity to VEN varied. Canine BCL2 protein was detected in all samples sensitive to VEN and was variably detected in resistant samples. All samples that lacked BCL2 were resistant to VEN. Conclusion and Clinical Importance: Neoplastic canine T lymphocytes are sensitive to VEN at concentrations achievable in vivo, thus VEN may be a novel therapeutic agent for treatment of canine T cell cancers. Detection of BCL2 protein is insufficient to predict in vitro sensitivity to VEN.
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    Inflammation and endothelial perturbation in canine abdominal surgery: the potential modulatory effect of lidocaine
    Donaldson, Liam Robert ( 2019)
    Complication rates following emergency laparotomy surgery are high, with organ dysfunction being a commonly encountered post-operative complication. Given the endothelium acts as the interface between the systemic circulation and the organs, its function is vital to maintaining organ health. The endothelium is in a constant state of flux, impacted largely by the local environment of which it is a part. In the presence of wide-spread systemic inflammation, inflammatory mediators precipitate change to the structure of the endothelial glycocalyx. These changes result in shedding of the endothelial glycocalyx and alteration of the endothelial phenotype. The endothelium may, as a result, lose the capacity to regulate vasomotor tone, and shift toward a pro-inflammatory and pro-coagulant state. This predisposes to reduced tissue oxygen delivery, and organ dysfunction may ensue. This thesis aimed to answer two key questions: does surgical trauma induced in canine patients undergoing emergent abdominal surgery invoke a systemic inflammatory response and subsequent endothelial activation? And if so, does lidocaine, a proposed immunomodulatory drug, mitigate this effect when given in the post-operative period? Chapter two provides a detailed review of endothelial structure and function, and current literature pertaining to systemic inflammation and endothelial activation in the context of abdominal surgery. Chapter two also examines the literature regarding the proposed mechanisms through which lidocaine acts as an immunomodulatory drug, and reviews publications that investigate the use of lidocaine as an anti-inflammatory drug in human patients after abdominal surgery. Chapter three is a randomized, blinded clinical trial quantifying the effect of emergency abdominal surgery on the concentration of markers of systemic inflammation and endothelial perturbation in canine patients in the post-operative period. The trial also assessed the potential use of lidocaine as a post-operative immunomodulatory therapy in dogs having undergone laparotomy. Fifty canine patients undergoing abdominal surgery were enrolled in the study. Patients were randomized into two separate groups: a study group receiving lidocaine intravenously, and a control group receiving 0.9% NaCl intravenously for a twelve-hour period following abdominal surgery. Blood samples were gathered prior to surgery, followed by six and twelve hours post-operatively. Concentrations of markers of systemic inflammation (IL-6) and markers of endothelial perturbation (VEGF and HA) were quantified via means of ELISA at each time point. Results revealed a significant increase in the concentration of markers of systemic inflammation and endothelial perturbation in post-operative blood samples. No immunomodulatory or endothelial preserving effect of lidocaine was appreciated.