Establishment of reference intervals for ultrasonographically derived caudal vena cava parameters from 110 healthy, lightly sedated cats

Abstract

Objectives The present study aimed to establish reference intervals (RIs) for ultrasonographically derived caudal vena cava (CVC) parameters in healthy cats. Methods A prospective, observational, experimental single-centre study involving 110 cats was conducted. Two trained operators scanned all cats in a randomised order. Two sets of cine loops per cat were conducted by each operator from the subxiphoid view with cats in lateral recumbency. Two blinded raters measured the narrowest inspiratory (CVCinsp) and widest expiratory (CVCexp) diameter over two separate respiratory cycles for each operator (four measurements in total for each rater) at the point the CVC crosses the diaphragm. The CVC collapsibility index (CVCCI) was calculated. Reference intervals and limits were calculated for CVC parameters with outliers removed to include the central 95% of CVC values and the non-parametric 90% confidence intervals (90% CIs). The CVCCI interval included the central 95th (2.5th and 97.5th) centiles bounded by the 90% CI. Intra- and inter-rater and intra- and inter-operator reliabilities were calculated for each parameter using a two-way random-effects model. A Bland–Altman plot was used to visualise the CVCCI between the two raters. Results In total, 880 measurements were included for each diameter and 440 CVCCI values were calculated. The CVC diameters were normally distributed, whereas the CVCCI was not. The calculated RIs were 1.4–6.1 mm for CVCinsp and 2.2–6.7 mm for CVCexp. The median (range) CVCCI was 23% (11–36%) with 2.5th and 97.5th centiles of 2% and 67%, respectively. There was a moderate to good intra-rater and intra-operator reliability for CVC diameter. The intra-rater reliability for the CVCCI was moderate. The inter-rater and inter-operator reliabilities for the CVCCI were poor. Conclusions and relevance The CVC RIs determined from the subxiphoid site in cats appear to be wider than those reported in dogs, and rater and operator variability is present. Whether precise measurements of CVC parameters are suitable to guide clinical decisions remains to be determined.