What are the parameters for Inferior Vena Cava (IVC) collapse?

From the Guidelines

The assessment of Inferior Vena Cava (IVC) collapse using ultrasound typically requires a collapse of greater than 50% during inspiration to indicate hypovolemia or fluid responsiveness. To properly evaluate IVC collapse, the IVC should be visualized in the subxiphoid long-axis view, measuring 2-3 cm from the right atrial junction during both inspiration and expiration. The formula for calculating IVC collapsibility index is: (maximum diameter - minimum diameter) / maximum diameter × 100%. A collapsibility index exceeding 50% generally suggests fluid responsiveness in spontaneously breathing patients, while values below 50% indicate adequate volume status. For mechanically ventilated patients, the opposite occurs - IVC distension during inspiration rather than collapse is assessed, with distensibility index >18% suggesting fluid responsiveness. Factors that can affect accurate measurement include obesity, increased abdominal pressure, right heart failure, pulmonary hypertension, and mechanical ventilation. The assessment should be performed with the patient in a supine position, and M-mode ultrasound is often used to better visualize the respiratory variation.

Key Parameters for IVC Collapse Assessment

• IVC diameter measurement: 1.0 to 2.0 cm from the junction with the right atrium, using the long-axis view 1
• Collapse of greater than 50% during inspiration to indicate hypovolemia or fluid responsiveness
• Collapsibility index calculation: (maximum diameter - minimum diameter) / maximum diameter × 100%
• Patient position: supine
• Ultrasound mode: M-mode for better visualization of respiratory variation

Clinical Considerations

• The relationship between IVC diameter and collapse can be used to estimate right atrial pressure, with a collapsibility index exceeding 50% suggesting normal right atrial pressure 1
• The assessment of IVC size and dilation can inform the plausibility of tamponade physiology in cases of uncertainty 1
• The evaluation of IVC size and collapsibility should be considered a basic skill for intensivists in the general and neuro intensive care unit population 1

From the Research

Parameters of IVC Collapse

The parameters for Inferior Vena Cava (IVC) collapse are as follows:

• IVC diameter: a dilated IVC (> 2.5 cm) with minimal collapsibility (less than 50%) had a sensitivity of 85.7% and specificity of 86.4% for predicting a volume overloaded fluid status 2
• IVC collapsibility index (CI):
  • IVC CI < 20% with no sniff suggests increased right atrial pressure and is inconsistent with overt hypovolemia in spontaneously breathing or ventilated patients 3
  • IVC CI ≥ 0.5 on admission suggests a volume shift from the central vein into the pulmonary vasculature 4
  • IVC maximum diameter < 2.1 cm, that collapses > 50% with or without a sniff is inconsistent with intravascular volume overload and suggests normal right atrial pressure (0-5 mmHg) 3
• Respiratory collapse of the IVC: reflects volume shift and subsequent fluid refill in acute heart failure syndrome 4
• IVC diameter and collapsibility: correlated significantly with N-terminal pro-B natriuretic peptide (NT-proBNP) in patients with heart failure, and may be useful in determining a patient's volume status 5

Diagnostic Performance

The diagnostic performance of IVC characteristics in predicting fluid status is as follows:

• The area under the curve (AOC) for predicting a volume overloaded fluid status using IVC size and collapsibility was 0.92 2
• The pooled sensitivity and specificity of IVC collapsibility index for predicting fluid responsiveness were 0.71 and 0.75, respectively 6
• The diagnostic odds ratio for IVC collapsibility index was 2.02 6