What are the parameters of Inferior Vena Cava (IVC) collapsibility in shock?

From the Guidelines

Inferior vena cava (IVC) collapsibility is a useful ultrasonographic parameter for assessing volume status in shock patients, with greater than 50% collapse during respiration suggesting hypovolemia. To measure IVC collapsibility, obtain a subxiphoid view of the IVC using ultrasound, measuring the maximum diameter during expiration and minimum diameter during inspiration, typically 2-3 cm from the right atrial junction. Calculate the collapsibility index using the formula: (maximum diameter - minimum diameter)/maximum diameter × 100%. A collapsibility index >50% in spontaneously breathing patients indicates volume responsiveness, while <50% suggests adequate filling. For mechanically ventilated patients, the opposite applies - distensibility >18% indicates fluid responsiveness. Normal IVC diameter ranges from 1.5-2.5 cm, with complete collapse suggesting severe hypovolemia. This assessment is valuable because it provides real-time, non-invasive hemodynamic information, though results should be interpreted cautiously in patients with right heart failure, pulmonary hypertension, increased intra-abdominal pressure, or those on high PEEP ventilation, as these conditions may affect IVC dynamics independently of volume status 1. The use of dynamic variables such as IVC collapsibility to predict fluid responsiveness is supported by recent guidelines, which suggest that dynamic over static variables be used to predict fluid responsiveness, where available 1. Key points to consider when using IVC collapsibility to assess volume status include:

• Measuring IVC diameter and collapsibility index using ultrasound
• Interpreting results in the context of the patient's clinical condition and other hemodynamic parameters
• Considering the potential impact of other conditions, such as right heart failure or pulmonary hypertension, on IVC dynamics. It is also important to note that IVC collapsibility is just one parameter that should be used in conjunction with other clinical and hemodynamic parameters to guide fluid management in shock patients. In clinical practice, the use of IVC collapsibility to guide fluid management can help to optimize fluid resuscitation and improve patient outcomes, as supported by recent guidelines 1.

From the Research

Parameters of IVC Collapsibility in Shock

The parameters of Inferior Vena Cava (IVC) collapsibility in shock can be assessed through various studies, which provide insight into the diagnostic utility of point-of-care ultrasound (PoCUS) for IVC size and collapsibility in predicting fluid status.

• IVC size and collapsibility can be used to predict volume overloaded fluid status, with a combined parameter of a dilated IVC (> 2.5 cm) with minimal collapsibility (less than 50%) showing a sensitivity of 85.7% and specificity of 86.4% 2.
• The IVC collapsibility index (IVCCI) can be used to estimate elevated general heart end-diastolic volume index (GEDVI) in septic shock patients, with a cut-off value of 12.9% predicting GEDVI < 600 ml/m2 3.
• IVC diameter and collapsibility index can be used to evaluate intravascular volume status in critically-ill patients, with a significant correlation between central venous pressure (CVP) and IVC-CI (r = -0.612, p < 0.001) 4.

Educational Intervention and Ultrasound Assessment

• An educational intervention can effectively teach fourth-year medical students how to utilize IVC US measurement and echocardiography to assist in volume assessment of patients presenting with shock, with a significant increase in knowledge and high learner satisfaction 5.
• Ultrasound-assessed IVC diameter response to trauma resuscitation after 1 hour can predict 24-hour fluid requirement, with IVCDMIN and IVCCI response to initial resuscitation predicting 24-hour fluid resuscitation requirements 6.

Key Findings

• IVC size and collapsibility can be used to predict fluid status in shock patients.
• IVCCI can be used to estimate elevated GEDVI in septic shock patients.
• IVC diameter and collapsibility index can be used to evaluate intravascular volume status in critically-ill patients.
• Educational intervention can effectively teach medical students how to utilize IVC US measurement and echocardiography.
• Ultrasound-assessed IVC diameter response to trauma resuscitation can predict 24-hour fluid requirement.