What are the benefits and risks of a Vexus (vascular ultrasound) scan?

VExUS (Venous Excess Ultrasound) Scan

What is VExUS?

VExUS is a point-of-care ultrasound protocol that rapidly assesses systemic venous congestion by integrating Doppler analysis of the inferior vena cava (IVC), hepatic vein, portal vein, and intrarenal veins to grade severity of fluid overload. 1, 2

Primary Benefits

Diagnostic Capabilities

• Provides real-time, non-invasive quantification of venous congestion that cannot be reliably detected through physical examination or laboratory tests alone 1
• Demonstrates substantial inter-rater reliability with a Kappa statistic of 0.71 and intraclass correlation coefficient of 0.83, meaning different clinicians interpret results consistently 3
• Strongly correlates with invasive hemodynamic measurements, showing significant associations with right atrial pressure (β = 11 for Grade 3, p < 0.01), mean pulmonary artery pressure (β = 15 for Grade 3, p < 0.01), and pulmonary capillary wedge pressure (β = 13 for Grade 3, p < 0.01) 4
• Superior predictive accuracy for elevated right atrial pressure (>10 mmHg) with area under the curve of 0.9, compared to IVC diameter alone (0.77) or IVC collapsibility index (0.65) 4

Clinical Applications

• Guides fluid management decisions by providing objective data on volume status, particularly valuable in critically ill patients where clinical assessment is unreliable 1, 2
• Feasible in perioperative settings with 91% successful scan completion rate across all timepoints in noncardiac surgery patients 5
• Interpretable by clinicians with diverse backgrounds including intensivists, emergency physicians, and interventional radiologists after appropriate training 3
• Enables bedside assessment without need for invasive monitoring or transport to radiology 2

Prognostic Value

• Identifies patients at risk for diuretic failure, with Grade 3 congestion showing significant association with poor weight loss during diuresis (p = 0.025) 4
• Detects subclinical venous congestion, as 50% of patients with normal preoperative VExUS developed postoperative congestion 5

Primary Risks and Limitations

Technical Challenges

• Requires comprehensive understanding of Doppler techniques and proper machine settings to avoid misinterpretation of waveforms 1
• Operator-dependent skill with potential for measurement errors if clinician lacks adequate training in ultrasound 1
• 9% scan failure rate even in experienced hands, typically due to body habitus, bowel gas, or patient positioning issues 5
• Improved accuracy with concurrent ECG tracing for timing cardiac cycles, though not always available 3

Clinical Interpretation Pitfalls

• No Grade 3 congestion observed in perioperative study despite 32% complication rate, suggesting VExUS may not capture all clinically relevant congestion patterns 5
• Lack of validated cutoffs for specific clinical decisions (e.g., when to initiate or stop diuresis) 4
• Venous congestion is common postoperatively (44% in PACU, 49% at 24 hours) but relationship to complications remains unclear 5
• No statistically significant association demonstrated between VExUS grade and 30-day complications or acute kidney injury in noncardiac surgery patients 5

Evidence Gaps

• Limited prospective validation for clinical outcomes, with most studies showing physiologic correlations rather than impact on morbidity or mortality 5, 4
• Unclear therapeutic thresholds - studies show associations with hemodynamic parameters but don't define when intervention improves outcomes 4
• Predominantly studied in cardiac and ICU populations, with less data in general medical or surgical patients 5, 4

Practical Implementation

Equipment Requirements

• Standard ultrasound machine with Doppler capability and ability to assess IVC, hepatic vein, portal vein, and intrarenal veins 1
• Phased array or curvilinear probe for adequate depth penetration 1
• ECG monitoring during scan improves inter-rater agreement and should be used when available 3

Key Technical Points

• Assess IVC diameter in subcostal view during respiratory cycle 1
• Obtain hepatic vein Doppler in right subcostal view, measuring systolic and diastolic flow patterns 1
• Evaluate portal vein pulsatility using spectral Doppler 1
• Measure intrarenal venous flow in lower pole of kidney using color Doppler to identify vessels 1

Common Pitfalls to Avoid

• Misidentifying vessels - use color Doppler to confirm vessel identity before spectral Doppler measurement 1
• Inadequate Doppler angle - maintain angle <60 degrees for accurate velocity measurements 1
• Respiratory artifact - obtain measurements during quiet breathing, not breath-holding 1
• Confusing arterial and venous waveforms - venous flow should be continuous with respiratory variation 1

Clinical Context

VExUS represents an emerging tool for bedside assessment of venous congestion that shows promise for guiding fluid management, but currently lacks robust evidence linking specific grades to improved clinical outcomes. While the technique demonstrates good reliability and correlates with invasive hemodynamic measurements, clinicians should interpret results in conjunction with other clinical data rather than using VExUS grades as sole determinants of therapy 5, 4, 3. The technique is most valuable when performed by trained operators with understanding of Doppler principles and potential artifacts 1.