# Assessing venous congestion in critical illness: advantages of the inferior vena cava shape change index over diameter

## TL;DR

This study shows that a new ultrasound measurement called the Shape Change Index (SCI) of the inferior vena cava is better than traditional diameter measurements for detecting venous congestion in critically ill patients.

## Contribution

The study introduces and validates the SCI as a more reliable indicator of venous congestion compared to IVC diameter.

## Key findings

- The SCI of IVC showed a stronger correlation with venous congestion grade than IVC diameter (Spearman’s ρ = 0.691 vs 0.490).
- SCI demonstrated better diagnostic discrimination (AUC = 0.864) compared to IVC diameter (AUC = 0.767) for detecting venous congestion.
- Higher SCI values were associated with greater disease severity, especially in less advanced stages of venous congestion.

## Abstract

The traditional Venous Excess Ultrasound (VExUS) scoring system relies on inferior vena cava (IVC) diameter measurements, which are affected by multiple confounding factors. The Shape Change Index (SCI) of IVC, defined as the ratio of short-axis diameter to long-axis diameter, may provide a more stable morphological indicator of venous filling.

In this prospective study, trained operators performed bedside ultrasonography to measure IVC diameter and calculate the SCI of IVC (short-axis diameter/long-axis diameter). Hepatic, portal, and renal venous Doppler waveforms were used to grade venous congestion (Grade 0–3). Diagnostic performance of SCI and IVC diameter for detecting venous congestion was evaluated using receiver operating characteristic(ROC) analysis, with additional exploratory analyses performed to further characterize incremental diagnostic value.

A total of 116 venous Doppler examinations from 84 critically ill adults were analyzed. The SCI of IVC demonstrated a stronger correlation with venous congestion grade than IVC diameter (Spearman’s ρ = 0.691 vs 0.490, both p < 0.001). For detecting any venous congestion (VExUS Grade ≥1 vs Grade 0), the SCI of IVC showed significantly better diagnostic discrimination than IVC diameter, with an area under the curve of 0.864 compared with 0.767, respectively (p = 0.044). The diagnostic advantage of SCI appeared to be more evident in examinations without advanced venous congestion. Higher SCI values were associated with greater disease severity.

The SCI of IVC demonstrates superior diagnostic performance compared with IVC diameter for the identification of venous congestion in critically ill patients, particularly at earlier or less advanced stages. These findings support the use of SCI as a complementary screening tool within the existing VExUS framework. Further multicenter studies are required to confirm its clinical utility and generalizability.