Point-of-care-ultrasound measurements of cardiovascular indices across awake, sedated, anesthetized, and recovered states in dogs.

Background: Point-of-care ultrasound (POCUS) assessment of intravascular volume in dogs commonly incorporates caudal vena cava (CVC) measurements, including the CVC-to-aorta ratio (CVC: Ao) and CVC collapsibility index (CVCCI). While these indices have been evaluated in awake dogs, the effects of sedation and anesthesia on these parameters remain unclear. Left ventricular end-diastolic diameter (LVEDD), a preload-sensitive echocardiographic measurement with established repeatability, may provide additional insight into cardiac loading conditions during anesthesia. Objective: To quantify CVC: Ao, CVCCI, and LVEDD in healthy dogs across four physiologic states and to evaluate the effects of anesthesia and systolic arterial pressure (SAP) on these indices, including intra-rater reliability. Animals: Eight purpose-bred, healthy adult neutered male Beagle dogs. Methods: In this prospective observational study, each dog underwent POCUS examination while awake, sedated, anesthetized, and recovered. CVC and aortic diameters were measured at paralumbar and iliac sites to calculate CVC: Ao; CVCCI was obtained from subxiphoid CVC measurements; and LVEDD was measured from a right parasternal short-axis view. SAP was recorded at each timepoint. Linear mixed-effects models assessed the effects of timepoint, SAP, and their interaction on ultrasound variables. Intra-rater reliability was evaluated using intraclass correlation coefficients. Results: SAP was lowest during anesthesia compared with awake and sedated states. LVEDD differed significantly by physiologic state and was smaller during anesthesia than during awake, sedated, or recovered states, while SAP was not an independent predictor of LVEDD. CVCCI varied across timepoints and demonstrated a strong positive association with SAP, with significant timepoint-SAP interactions. CVC: Ao ratios showed minimal or inconsistent changes across physiologic states. Intra-rater reliability was good for LVEDD, moderate to excellent for CVCCI, and poor to moderate for CVC: Ao measurements. Conclusions and clinical importance: In healthy dogs under anesthesia, LVEDD is a reproducible ultrasound measurement that reflects anesthesia-associated changes, independent of systolic arterial pressure, and should not be used independently to assess intravascular volume. CVCCI is strongly pressure-dependent under anesthesia and should not be interpreted as a standalone indicator of intravascular volume. CVC: Ao showed minimal state-dependent variation, however, it had lower repeatability, limiting its ability to assess intravascular volume in anesthetized dogs.