Ultrasonographic estimation of central venous pressure using the caudal vena cava to aorta ratio in dogs: a proof-of-concept study

Context Central venous pressure (CVP) might be used to guide fluid therapy in critically ill patients, but its invasive nature and associated risks have prompted growing interest in non-invasive alternatives such as ultrasonographic vascular indices. Objectives To evaluate the correlation between the caudal vena cava (CVC) to aorta (Ao) (CVC:Ao) ratio and central venous pressure (CVP) and explore the use of this correlation for discriminating CVP values. Materials and methods Intermittent CVP measurements were obtained using a water-filled fluid column in dogs admitted for renal replacement therapy. Low (LCVP), normal (NCVP) and high CVP (HCVP) were defined as values of <0, between 0 and 5, and >5 cmH 2 O (centimeters of water pressure), respectively. The sonographic assessment of volaemia (SAV) protocol was used to obtain the CVC:Ao ratio in the end-expiratory phase. Results Fourteen dogs and 28 CVC:Ao ratio-CVP paired measurements were included. The CVP (in cmH 2 O) was estimated from the CVC:Ao ratio using the generated equation CVP = 20.9*(CVC:Ao)–19.44 ( R = 0.69, p < 0.0001). The median CVC:Ao ratios differed significantly among groups at 0.91, 1.00, and 1.12 for LCVP, NCVP and HCVP, respectively ( p = 0.0014). Using a CVC:Ao ratio <0.97, the sensitivity and specificity for detecting LCVP were 87.5 and 72.7%, respectively. Using a CVC:Ao ratio >1.09, the sensitivity and specificity for detecting HCVP were 66.7 and 90.9%, respectively. Clinical significance The CVC:Ao ratio may be used as a surrogate non-invasive marker for estimating CVP in spontaneously breathing dogs. A CVP < 0 cmH 2 O is likely if the CVC:Ao ratio is <0.97, and a CVP > 5 cmH 2 O is likely if the ratio is >1.09.