Establishment of reference values of the caudal vena cava by fast-ultrasonography through different views in healthy dogs

Background Clinical assessment of intravascular volume status is challenging. In humans, ultrasonographic assessment of the inferior vena cava diameter, directly or as a ratio to the aortic diameter is used to estimate intravascular volume status. Objectives To ultrasonographically obtain reference values (RV) for caudal vena cava diameter (CVCD), area (CVCa) and aortic ratios using 3 views in awake healthy dogs. Animals One hundred and twenty-six healthy adult dogs from clients, students, faculty, or staff. Methods Prospective, multicenter, observational study. Two observer pairs evaluated CVCD by a longitudinal subxiphoid view (SV), a transverse 11th-13th right hepatic intercostal view (HV), and a longitudinal right paralumbar view (PV). Inter-rater agreements were estimated using concordance correlation coefficients (CCC). For body weight (BW)-dependent variables, RVs were calculated using allometric scaling for variables with a CCC ≥ 0.7. Results The CCC was ≤0.43 for the CVC/aorta ratio at the PV and ≤0.43 in both inspiration and expiration for CVC at the SV. The RVs using allometric scaling for CVCa at the HV for inspiration, expiration, and for CVCD at the PV were 6.16 × BW0.762, 7.24 × BW0.787, 2.79 × BW0.390, respectively. Conclusions and Clinical Importance The CVCD, measured at the HV and PV in healthy awake dogs of various breeds has good inter-rater agreement suggesting these sites are reliable in measuring CVCD. Established RVs for CVCD for these sites need further comparison to results obtained in hypovolemic and hypervolemic dogs to determine their usefulness to evaluate volume status in dogs.