Effects of general anaesthesia and intravenous fluid therapy on renal biomarkers in cats undergoing ovariohysterectomy : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University, Manawatu, New Zealand

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Traditional screening tests used to evaluate renal function have been demonstrated to be insensitive in detecting early kidney damage, such as subclinical acute kidney injury. It is probable that general anaesthesia and routinely performed surgical procedures could cause subclinical changes in the renal structure, predisposing the animal to subsequent functional impairment. However, these active changes might go undetected while screening using traditional renal markers, such as serum creatinine (SCr) and blood urea nitrogen (BUN). Novel urinary biomarkers, that indicate renal injury earlier than conventional markers, have been extensively studied in humans during the perioperative period. A feline model of mild acute kidney injury, potentially induced through general anaesthesia during routine surgeries, may prove useful in testing novel renal biomarkers and providing insight into the effects of anaesthesia on kidneys. A randomised controlled trial was performed using 60 healthy cats presented to the Massey University Veterinary Teaching Hospital for routine ovariohysterectomy. Blood and urine samples were collected immediately before (0 h), and after (24 and 48 h) anaesthesia and spay surgery. Traditional renal marker levels (SCr, BUN) were measured from the serum samples. Commercial assays were used to detect the levels of novel markers, such as N-acetyl-β-D glucosaminidase (NAG) enzyme, Neutrophil Gelatinase-associated Lipocalin (NGAL), Retinol Binding Protein (RBP) and Kidney Injury Molecule-1 (KIM-1), in the urine samples. This study aimed to use these urinary markers to investigate the effects of general anaesthesia and intraoperative fluid therapy on feline renal structure. Statistical tests such as t-test and ANOVA were conducted to establish differences in renal marker values between the time points and between treatment groups. Upon comparing the changes in renal marker concentrations, the study found no measurable evidence of structural or functional kidney damage in the cats. This is plausible since the vital parameters, such as arterial blood pressure and oxygenation levels, of the study cats were maintained within or near the borderline physiological range throughout the surgical procedure, resulting in the apparent absence of assessable kidney damage postoperatively. It is inferred that a more severe form of renal injury would be required to test the sensitivity of these novel renal markers in cats.
Figure 3 is re-used with permission.