Is respiratory variation greater than 50% of inferior vena cava (IVC) caliber of 1.3cm associated with right atrial (RA) pressure of 3mmHg?

From the Guidelines

Yes, respiratory variation greater than 50%, IVC caliber of 1.3 cm, and RA pressure of 3 mmHg are determined together as part of a comprehensive assessment of right atrial pressure and volume status. These measurements are typically obtained during an echocardiographic examination, as recommended by the American Society of Echocardiography and the European Association of Cardiovascular Imaging 1. The inferior vena cava (IVC) diameter and its respiratory variation provide valuable information about central venous pressure. A small IVC diameter (1.3 cm) with significant respiratory variation (>50% collapse during inspiration) suggests low right atrial pressure, which is consistent with the measured RA pressure of 3 mmHg, as indicated by the collapsibility index 1.

Some key points to consider when interpreting these measurements include:

• The IVC diameter should be measured in the subcostal view with the patient in the supine position at 1.0 to 2.0 cm from the junction with the right atrium, using the long-axis view 1.
• The diameter of the IVC decreases in response to inspiration when the negative intrathoracic pressure leads to an increase in RV filling from the systemic veins 1.
• The relationship between IVC diameter, collapse, and RA pressure may be quantified as the collapsibility index, which can help guide the determination of systolic pulmonary artery pressure 1.
• In scenarios where IVC diameter and collapse do not fit the typical paradigm, an intermediate value of RA pressure or other indices of RA pressure should be integrated to downgrade or upgrade to the normal or high values of RA pressure 1.

This integrated approach improves accuracy in assessing volume status, which is crucial for managing patients with heart failure, shock, or other conditions where fluid management is critical. By considering the respiratory variation, IVC caliber, and RA pressure together, clinicians can make more informed decisions about patient care.

From the Research

Determining Fluid Responsiveness

• The respiratory variation in inferior vena cava (IVC) diameter is used as a guide to fluid therapy in mechanically ventilated patients 2.
• A study found that a 12% DeltaD(IVC) cut-off value allowed identification of responders with positive and negative predictive values of 93% and 92%, respectively 2.
• However, another study found that respiratory variation in IVC diameter has limited ability to predict fluid responsiveness, particularly in spontaneously ventilating patients 3.

Relationship Between IVC Diameter and Fluid Responsiveness

• The distensibility index of the IVC (dIVC) was found to be a reliable predictor of fluid responsiveness in mechanically ventilated septic patients, with a threshold dIVC of 18% discriminating responders and non-responders with 90% sensitivity and 90% specificity 4.
• However, a study found that dIVC should be used with caution when critically ill patients on controlled mechanical ventilation display normal right ventricular function in combination with abnormal left ventricular systolic function 5.

Effect of Mechanical Ventilator Settings on IVC Diameter

• A study found that the respiratory changes of the IVC diameter and echocardiographic parameters showed no significant difference in separate mechanical ventilator settings 6.
• The results of this study suggest that IVC related parameters are not affected with different ventilatory settings 6.

Specific Values and Determination

• The question asks about the respiratory variation > 50 % IVC caliber 1.3cm, RA pressure 3mmhg, but there is no direct evidence in the provided studies to determine if these specific values are determined together 2, 3, 5, 4, 6.