From the Guidelines
The finding of an inferior vena cava (IVC) that is less than 2cm in diameter with greater than 50% collapse suggests normal or low central venous pressure (CVP) of 3 mm Hg, as indicated by the collapsibility index 1. This indicates the patient is likely euvolemic or hypovolemic. In a clinical setting, this finding suggests the patient can likely tolerate additional fluid administration if needed.
- Key points to consider:
- IVC diameter and collapse are used to estimate right atrial (RA) pressure, with an IVC diameter < 2.1 cm that collapses > 50% with a sniff suggesting normal RA pressure 1.
- The physiological basis for this finding is that during inspiration, negative intrathoracic pressure increases venous return to the right atrium, causing the compliant IVC to collapse when intravascular volume is not excessive.
- For patients requiring volume resuscitation, consider administering crystalloids such as normal saline or lactated Ringer's solution at 10-20 mL/kg initially, reassessing after each bolus.
- This IVC measurement is commonly assessed using bedside ultrasound during inspiration and expiration to evaluate volume status, and should be interpreted alongside other clinical parameters such as blood pressure, heart rate, urine output, and physical examination findings rather than in isolation.
- Clinical applications:
- Critical care settings: managing fluid status in patients with shock, sepsis, or heart failure.
- Bedside ultrasound: a useful tool for evaluating volume status and guiding fluid administration.
From the Research
IVC Collapsibility Index
- The IVC collapsibility index (CI) is a dynamic noninvasive point-of-care estimate of relative intravascular volume, measured by ultrasound 2.
- A study found that an 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) 2.
- The goal for IVC CI generally ranges from 20% to 50%, respecting potential biases to interpretation and overriding clinical considerations 2.
Fluid Resuscitation
- The choice of fluid to be used in the resuscitation of critically-ill patients remains a matter of debate, with no studies demonstrating a beneficial effect on survival of one type of fluid over another 3, 4.
- Crystalloid solutions, such as Ringer's lactate, may be preferable to normal saline as they reduce the risk of hyperchloraemic acidosis, which has been associated with impaired renal function 3.
- Colloid solutions, such as albumin, are effective but expensive, while hydroxyethyl starch solutions have been associated with detrimental effects on renal function 3, 4.
Clinical Application
- IVC ultrasound can be applied to guide volume management of patients with acute or chronic kidney disorders, particularly those with complex comorbidities requiring hospitalization or intensive care 2.
- Patients with lower IVC CI are more likely to tolerate ultrafiltration with hemodialysis or improve cardiac output with ultrafiltration 2.
- The choice of fluid is not only contingent on the restoration of intravascular volume, but also on the adverse effects that follow fluid resuscitation, particularly in older patients or those at risk of pulmonary edema 5.