Accurate assessment of intravascular volume is essential in critically ill and postoperative patients. Although CVP is widely used, it is invasive and associated with complications such as pneumothorax and catheter-related infections. Ultrasound measurement of IVC diameter and collapsibility index provides a rapid, bedside, noninvasive alternative. This study evaluated the correlation between IVC-derived indices and directly measured CVP in postoperative ICU patients.

METHODS

Study design and setting: A cross-sectional study was conducted in the postoperative ICU.

Participants: Thirty adult patients (18–80 years) who were mechanically ventilated and had a CVP catheter in situ were included. Exclusion criteria: spontaneous breathing, pulmonary hypertension, severe tricuspid regurgitation, deep vein thrombosis, pregnancy, right-sided pneumothorax, or central line via subclavian/femoral route.

Measurements: IVC diameters were measured using a Mindray Z6 ultrasound system with a curvilinear probe in the subxiphoid long-axis view. Maximum (end-expiratory) and minimum (end-inspiratory) diameters were recorded. Collapsibility index was calculated as (IVCmax − IVCmin) / IVCmax. CVP was measured using a saline manometer zeroed at the level of the right atrium. Statistical analysis was performed using SPSS v26. Bivariate Spearman correlation was used for non-normally distributed data. Significance was set at p < 0.05.

Ethical considerations: The study was approved by the Institutional Ethics Committee and informed consent was obtained from patients or their caregivers.

RESULTS

Baseline characteristics and main hemodynamic/IVC measurements are presented in Tables 2 and 3. Correlation results are shown in Tables 4 and 5. Figures 1 and 2 illustrate the CVP–IVC relationships.

Table 1. Distribution of age among study subjects (N = 30)

Table 2. Distribution of mean and SD of CVP and IVC parameters (N = 30)

Table 3. Correlation between CVP and maximum IVC diameter (N = 30)

*Significant correlation (Spearman).

Table 4. Correlation between CVP and IVC collapsibility index (N = 30)

Not statistically significant.

Figures

Figure 1. Correlation between CVP and maximum IVC diameter (significant positive correlation)

Figure 2. Correlation between CVP and IVC collapsibility index (non-significant correlation)

DISCUSSION

In this study, maximum IVC diameter had a strong positive correlation with CVP, suggesting it may be used as a reliable noninvasive marker of intravascular volume status. IVC collapsibility index showed poor correlation with CVP in this cohort. These results align with several prior studies demonstrating variable performance of IVC-derived indices depending on patient population and ventilation settings. Limitations include single-center design, relatively small sample size, and lack of preoperative fluid status stratification. Future studies should evaluate diagnostic accuracy against a gold standard in larger cohorts.

CONCLUSION

Maximum IVC diameter measured by ultrasonography correlates strongly with CVP and may serve as a noninvasive alternative for assessing intravascular fluid status. Collapsibility index did not show significant correlation in this sample.

Acknowledgments: We thank the Department of Anesthesiology, for their support.

Conflict of Interest: None declared.

REFERENCES

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