Echocardiographic assessment of hemodynamic changes produced by two methods of inducing fluid deficit in dogs

Background: Hydration status is important to the cardiovascular system because of its effects on preload. Decreased preload can alter echocardiographic measurements of systolic and diastolic function, potentially confounding interpretation of results. Hypothesis/Objectives: Mild fluid deficits are associated with measurable echocardiographic changes that are validated by physical and biochemical markers of decreased intravascular volume. Animals: Twenty-five healthy staff/student-owned dogs with no evidence of cardiac or renal disease. Methods: Prospective, interventional laboratory study. Dogs were randomly assigned to water deprivation (WD) alone for 8 hours (n=13) or to furosemide treatment (FTx, 2.5mg/kg IV) followed by WD for 8 hours (n=12). Echocardiograms, biochemical sampling, and physical parameters were measured at baseline, and after 4 and 8 hours. Results: Both protocols induced fluid deficit as indicated by significant (P o.00001) decreases in weight at 4 hours (WD, 1.1%; FTx, 3.7%) and 8 hours (WD, 2.7%; FTx, 4.5%). Furosemide significantly decreased left ventricular end-diastolic volume (54.3±19.3-42.1±17.3mL, P<.0001), cardiac index (4.2±1.1-2.9±0.9L/min/M², P<.0001), and mitral valve E wave velocity (0.79±0.2-0.66±0.2m/s, P=.0004). These changes were accompanied by significant increases in blood urea nitrogen concentration (13.8±2.6-14.8±2.7mg/dL, P=.04), vasopressin concentration (1.4±1.2-3.3±1.9pg/mL, P=.045), and PCV (49.8±4.5-53.2±6.5%, P=.006). Effects of water deprivation alone were similar, but less pronounced. Conclusions and Clinical Importance: Mild fluid deficits have measurable hemodynamic effects in dogs. Hydration status should be considered when evaluating cardiac function by echocardiogram.