Influence of the Respiratory Cycle on Caudal Vena Cava Diameter Measured by Sonography in Healthy Foals: A Pilot Study

Abstract

Background

Intravascular volume assessment in foals is challenging. In humans, intravascular volume status is estimated by the caudal vena cava ( CVC) collapsibility index ( CVC‐ CI) defined as ( CVC diameter at maximum expiration [ CVC _max] – CVC diameter at minimal inspiration [ CVC _min])/ CVC _max × 100%.

Hypothesis/Objectives

To determine whether the CVC could be sonographically measured in healthy foals, determine differences in CVC _max and CVC _min, and calculate inter‐ and intrarater variability between 2 examiners. We hypothesized that the CVC could be measured sonographically at the subxiphoid view and that there would be a difference between CVC _max and CVC _min values.

Animals

Sixty privately owned foals <1‐month‐old.

Methods

Prospective study. A longitudinal subxiphoid sonographic window in standing foals was used. The CVC _max and CVC _min were analyzed by a linear mixed effect model. Inter‐rater agreement and intrarater variability were expressed by Bland‐Altman and intraclass correlation coefficients, respectively.

Results

Measurements were attained from 58 of 60 foals with mean age of 15 ± 7.9 days and mean weight of 75.7 ± 17.7 kg. The CVC _max was significantly different from CVC _min ( D = 0.515, SE = 0.031, P < 0.001). Inter‐rater agreement of the CVC‐ CI differed by an average of −0.9% (95% limits of agreement, −12.5 to +10.7%). Intrarater variability of CVC _max was 0.540 and 0.545, of CVC _min was 0.550 and 0.594, and of CVC‐ CI was 0.894 and 0.853 for observers 1 and 2, respectively.

Conclusions and Clinical Importance

These results indicate it is possible to reliably measure the CVC sonographically in healthy foals, and the CVC‐ CI may prove useful in assessing the intravascular volume status in hypovolemic foals.