Ultrasound measurements of the caudal vena cava before and after blood donation in 9 greyhound dogs.

This prospective study evaluated variation in the diameter of the caudal vena cava (DCdVC) as a marker of change in intravascular volume before and after blood donation in greyhound dogs. A preliminary study determined that the DCdVC increased with body weight. Nine greyhound blood donors had ultrasonographic images acquired of the maximum and minimum DCdVCs in transverse and sagittal orientations and sagittal aortic diameter (AoD) before and after blood donation. The collapsibility index = [(maximal mean transverse DCdVC - minimal mean transverse DCdVC)/maximal mean transverse DCdVC] and transverse DCdVC:AoD ratio were calculated for each dog. In the greyhounds, the changes in mean minimal and maximal transverse DCdVC (0.69 and 0.84 mm, respectively) and sagittal mean maximal DCdVC (0.9 mm) and collapsibility index (0.018) were significantly different (P < 0.05) before and after blood donation. While statistically significant, the magnitude of DCdVC change found in this limited number of greyhound dogs with 8% intravascular volume loss during blood donation was small. This magnitude of change is likely indistinguishable in clinical patients.