How does the inferior vena cava (IVC) with respiratory variation help determine volume status?

From the Guidelines

The inferior vena cava (IVC) diameter and its respiratory variation are crucial in determining a patient's volume status, with a small and/or collapsible IVC indicating low volume status, as suggested by the 2020 ESC guidelines for the diagnosis and management of acute pulmonary embolism 1.

Key Points to Consider

• The IVC diameter and its respiratory variation can be used to assess volume status, with a small and/or collapsible IVC indicating low volume status.
• In hypovolemic states, the IVC appears small (<1.5 cm diameter) with greater than 50% collapse during inspiration, indicating fluid responsiveness.
• Conversely, in hypervolemic states, the IVC appears distended (>2.5 cm) with minimal (<50%) or no respiratory variation.
• Euvolemic patients typically show moderate respiratory variation with an IVC diameter between 1.5-2.5 cm.

Clinical Application

• Assessment of the IVC using ultrasound can help guide fluid management decisions in critically ill patients.
• The physiological basis for this phenomenon is that during inspiration, negative intrathoracic pressure increases venous return to the right atrium, causing the compliant IVC to collapse if the patient has reduced intravascular volume.
• In fluid-overloaded states, the IVC remains distended throughout the respiratory cycle due to elevated right atrial pressures.
• This non-invasive bedside technique provides immediate information about volume status, though results should be interpreted in the context of the patient's clinical condition, as factors like mechanical ventilation, cardiac function, and intra-abdominal pressure can affect IVC dynamics, as noted in the 2017 WSES guidelines for management of intra-abdominal infections 1 and the 2016 experts' opinion on management of hemodynamics in ARDS patients 1.

From the Research

Inferior Vena Cava and Volume Status

The inferior vena cava (IVC) with respiratory variation can be used to determine volume status in patients.

• The IVC diameter can be measured using ultrasonography, and its variation with respiration can indicate the patient's volume status 2, 3, 4.
• A decrease in IVC diameter during inspiration (IVCi) and an increase during expiration (IVCe) can indicate hypovolemia, while a minimal change in IVC diameter with respiration can indicate euvolemia or hypervolemia 2, 4.
• The IVC collapsibility index (CI) and distensibility index can also be used to assess volume status, with a higher CI indicating hypovolemia and a lower CI indicating euvolemia or hypervolemia 3.

Diagnostic Performance of IVC Ultrasound

The diagnostic performance of IVC ultrasound in predicting volume overloaded fluid status has been evaluated in several studies.

• A study found that a dilated IVC (> 2.5 cm) with minimal collapsibility (< 50%) had a sensitivity of 85.7% and specificity of 86.4% in predicting volume overloaded fluid status 5.
• Another study found that the IVC diameter was significantly lower in hypovolemic patients compared to euvolemic patients, with a mean difference of 6.3 mm (95% CI: 6.0-6.5 mm) 6.

Clinical Applications of IVC Ultrasound

IVC ultrasound has several clinical applications, including:

• Guiding fluid administration in patients with undifferentiated hypotension 5.
• Evaluating the response to fluid resuscitation in hypovolemic patients 2, 4.
• Assessing volume overload and guiding ultrafiltration goals in patients with heart failure or renal failure 3.
• Predicting intra-dialytic hypotension and assessing acute decompensated heart failure 3.