Assessment of Venous Return During Volume Expansion: a Prospective Observational Study

Assessment of Venous Return During Volume Expansion: a Prospective Observational Study

According to Guyton's model of venous return, the fluids that effectively increase cardiac output are those that, once administered, increase the vascular stressed volume, thereby increasing the mean systemic filling pressure (Pms) without increasing the central venous pressure (CVP). In this way, since the gradient between Pms and CVP increases, venous return-and consequently cardiac output-also increases.

In cases where physiologically ineffective fluids are administered, the situation arises in which, in addition to increasing the stressed volume and thus Pms, CVP also increases. As a result, the gradient between Pms and CVP remains unchanged, and cardiac output does not increase.

The hypothesis is that only a portion of the fluids administered during volume expansion are actually effective in increasing the gradient between Pms and CVP.

Inclusion Criteria:

• Critically ill patients admitted to the intensive care unit
• Invasive or minimally invasive hemodynamic monitoring
• Clinical indication for volume expansion with 500 mL of crystalloids

Exclusion Criteria:

• Suspected or confirmed pregnancy
• Clinical conditions that may reduce the reliability of hemodynamic monitoring:
• Severe aortic stenosis or regurgitation
• Severe mitral stenosis or regurgitation
• History of peripheral arterial disease
• Clinical contraindications to the supine position