Ultrasonographic caudal vena cava to aorta ratio changes during blood donation and crystalloid fluid resuscitation in cats

Objectives The aim of the present study was to evaluate caudal vena cava:aorta (CVC:Ao) ratio changes at the hepatorenal location as an ultrasonographic indicator for detecting acute blood loss and monitoring fluid therapy response in cats undergoing blood donation and subsequent crystalloid administration. Methods A total of 10 healthy adult cats scheduled for routine blood donation were sedated with ketamine and midazolam. Ultrasonographic measurement of the caudal vena cava (CVC) and aorta (Ao) at the hepatorenal location was performed at baseline, after 10 ml/kg blood donation, and at 5 and 15 mins after intravenous administration of an equal volume of Hartmann’s solution. Triplicate measurements of the CVC:Ao ratio were averaged at each time point and compared using linear mixed models. Results The mean (±SD) CVC:Ao ratio at baseline was 1.01 ± 0.07 and decreased to 0.92 ± 0.09 after blood donation, although this change was not statistically significant ( P = 0.06). After fluid administration, mean ratios increased to 1.02 ± 0.12 and 1.00 ± 0.08 at 5 and 15 mins, respectively. Only the difference between post-donation and 5 mins post-fluid resuscitation values reached statistical significance (mean difference –0.1, 95% confidence interval [CI] –0.2 to –0.1; P = 0.03). Intra-observer reliability was modest (intraclass correlation coefficient = 0.48, 95% CI 0.29–0.66), although the within-observer SD was 0.09. Conclusions and clinical relevance The CVC:Ao ratio at the hepatorenal location demonstrated limited sensitivity for detecting hypovolemia induced by 10 ml/kg blood donation in cats. However, the significant increase observed after fluid resuscitation suggests this measurement may be useful for monitoring response to fluid therapy in cats with previously documented hypovolaemia. The modest intra-observer reliability despite low SD highlights challenges in consistently measuring small vascular structures in cats.