Study highlights renal Doppler marker for canine hypovolemia
Bottom line
A new study in Veterinary Sciences suggests renal artery resistive index, or RRI, may outperform more familiar ultrasound volume markers for identifying hypovolemia in dogs. In the case-control study, researchers evaluated 30 dogs, including 15 hypovolemic dogs and 15 controls, and found hypovolemic dogs had higher RRI values and smaller caudal vena cava and aortic diameters on Doppler ultrasound. Receiver operating characteristic analysis showed strong diagnostic performance for RRI, CVC diameter, and aortic diameter, but multivariate analysis identified RRI as the only independent early diagnostic marker. The authors also reported that BUN and the BUN:creatinine ratio increased in hypovolemic dogs, while creatinine stayed unchanged. (mdpi.com)
Why it matters: For veterinary teams managing shock, dehydration, hemorrhage, or other causes of low circulating volume, the findings add to growing interest in bedside ultrasound as a faster, less invasive way to assess perfusion status. Prior canine POCUS work has shown that CVC diameter can fall with hypovolemia, but the CVC:Ao ratio has produced mixed results across studies, especially in severe or experimentally induced shock. This new paper suggests renal Doppler, specifically RRI, could offer a more sensitive early signal than hematology, chemistry, or vessel ratios alone, although the study was small and further validation in broader clinical populations will matter before it changes frontline protocols. (mdpi.com)
What to watch: Watch for follow-up studies in larger, client-owned dog populations, especially work testing whether RRI improves real-time triage or fluid decision-making in emergency and critical care settings. (mdpi.com)
A newly published Veterinary Sciences study points to renal artery resistive index as a potentially stronger ultrasound marker of hypovolemia in dogs than caudal vena cava or aortic measurements alone. The April 19, 2026 paper, from Ghada Ashraf and colleagues, examined 30 dogs and found that hypovolemic patients had markedly increased RRI and significantly reduced CVC and aortic diameters compared with controls. On multivariate analysis, RRI emerged as the only independent early diagnostic marker among the variables tested. (mdpi.com)
That finding lands in an area of active interest for small animal emergency and critical care. Hypovolemia can be hard to assess early because dogs may compensate well enough to preserve blood pressure until disease is advanced. Earlier veterinary literature has already explored POCUS-based volume assessment using the caudal vena cava, aorta, and CVC:Ao ratio, but results have been inconsistent depending on the model, scan location, anesthesia status, and whether shock developed acutely or more gradually. A 2024 Frontiers in Veterinary Science study in experimentally induced hemorrhagic shock, for example, found that CVC diameter decreased with severe hypovolemia, while the CVC:Ao ratio did not significantly change because both the CVC and aorta became smaller. (frontiersin.org)
In the new MDPI paper, the authors compared 15 hypovolemic dogs with 15 controls and paired ultrasound findings with clinical, biochemical, and hematologic data. They reported significantly higher RRI, significantly lower CVC diameter, and significantly lower aortic diameter in hypovolemic dogs. Biochemically, BUN and the BUN:Cr ratio increased, while creatinine did not, and hematology offered limited discrimination aside from mild packed cell volume increases. ROC analysis showed excellent performance for RRI, with an AUC of 0.99, compared with 0.93 for CVC diameter and 0.88 for aortic diameter; the CVC:Ao ratio and hematologic markers performed poorly. Logistic regression supported diagnostic value for RRI, CVC diameter, aortic diameter, and BUN, but only RRI remained independently significant in the final model. (mdpi.com)
There doesn’t yet appear to be published outside commentary on this specific paper, but the broader field has been moving in this direction. Reviews of volume assessment in small animals note that static clinical parameters can be misleading, while ultrasound offers a repeatable, noninvasive bedside tool. At the same time, recent canine POCUS studies have emphasized that CVC-based measures are useful but imperfect, with performance varying by technique and clinical context. That makes the RRI result notable: it suggests intrarenal Doppler may capture perfusion changes that simple vessel size measurements can miss. (frontiersin.org)
Why it matters: For veterinary professionals, the practical question is whether this changes how hypovolemia gets recognized before overt decompensation. The study supports RRI as a promising adjunct when the exam, blood pressure, PCV/TS, or routine chemistry don’t fully explain a dog’s perfusion status. That could be relevant in emergency presentations involving vomiting and diarrhea, hemorrhage, sepsis, perioperative instability, or poor intake, where early volume assessment shapes fluid plans and monitoring intensity. Still, RRI is more technically demanding than measuring a large vessel, and the paper does not by itself establish training standards, cutoff implementation in general practice, or whether RRI-guided decisions improve outcomes. (mdpi.com)
The study also fits with a larger message from recent canine ultrasound research: one measurement is unlikely to be enough. The 2024 Frontiers hemorrhagic shock study found CVC diameter tracked severe intravascular volume loss, but not mean arterial pressure or cardiac output, and highlighted how compensatory vascular tone can complicate interpretation of CVC:Ao. In that context, adding renal Doppler may help clinicians build a fuller picture rather than relying on a single static marker. (frontiersin.org)
What to watch: The next step is external validation, ideally in larger cohorts of client-owned dogs with naturally occurring hypovolemia and mixed causes of shock, along with work on reproducibility, operator training, and clinically useful cutoff values before RRI can move from promising marker to routine bedside tool. (mdpi.com)