Department of Critical Care

Assessment of the Inferior Vena Cava (IVC)

Interrogation of the inferior vena cava (IVC) plays an important role in the performance of critical care echocardiography and provides insight into the systemic hemodynamics of patients with critical illness. In conjunction with clinical examination, IVC assessment can be used as a surrogate marker of right atrial pressure and fluid responsiveness. 1–3 Non-invasive measurements of IVC size and collapsibility may allow one to grossly infer central venous pressure. 1–3 Sonographic capture of the IVC can be performed readily with good inter-rater reliability after a brief training period.4 The arguments for and against the use of IVC as a surrogate marker for volume status and fluid responsiveness are well described in the recent published literature.5–8 Although the IVC can imaged readily after a brief, focused training period,4 clinical integration requires thoughtful consideration of contextual factors.

Important considerations include:

  1. Clinical assessment and pre-test probability of hypovolemia, hypervolemia or euvolemia?
  2. Spontaneously-breathing or mechanically-ventilated?
  3. Risk of error in integration or sonographic acquistion9
  4. Confounding factors, which may invalidate conventional principles of IVC assessment including pericardial tamponade, pre-existing pulmonary hypertension, abdominal compartment syndrome, severe tricuspid regurgitation, right ventricular myocardial infarction, others10

 

In the following section, we will outline key principles of IVC assessment including image acquisition, assessment, and integration. 


With the patient in the supine position and the probe placed in the sub-xyphoid position with marker cephalad, the IVC lies to the anatomical right of midline. Three components of the IVC must be identified; an anechoic tubular structure that traverses through the liver, right atrium-IVC junction, and hepatic vein (HV). 

It is crucial to recognize that the aorta, which lies to the anatomic left of midline, may mimic the appearance of the IVC. The aorta is covered in echogenic adipose tissue and does not join the right atrium. These structure are easily visualized, except in cases of intervening air in the abdominal viscera.

Measurement of IVC size and collapsibility can be performed in the long axis view, perpendicular to direction of the IVC and approximately 0.5 to 3.0 cm proximal to RA entrance. Measurement should be performed at end-expiration in the spontaneously breathing patient. An additional measurement can be performed by asking the patient to perform a gentle sniff for measurement of collapsibility. M-mode imaging is generally used to perform the measurement but does introduce an additional concern, that is if the beam is off the centre axis of the IVC the widest diameter may not be shown.


The IVC dynamically responds to respiro-phasic cycling and is different depending on whether the patient is breathing spontaneously or is mechanically ventilated. In a patient with spontaneous breathing, the IVC will decrease in size (diameter) secondary to negative intra-thoracic pressure during inspiration. By analyzing the IVC size and collapsibility, we can derive a gross right atrial pressure (as shown in the table to the right). Alternatively, positive pressure ventilation leads to IVC distension with inspiration (commonly called a 'distensibility index'). IVC measurements on mechanical ventilation will be covered in the video below (to be posted).

The following video tutorial describes sonographic assessment of the IVC in volume status. Also discusses considerations and confounding factors in assessment of the critically ill patient.



References

1. Ommen SR, Nishimura RA, Hurrell DG, Klarich KW. Assessment of right atrial pressure with 2-dimensional and Doppler echocardiography: a simultaneous catheterization and echocardiographic study. Mayo Clin Proc. 2000;75:24-29.

 2. Brennan JM, Blair JE, Goonewardena S, et al. A Comparison by Medicine Residents of Physical Examination Versus Hand-Carried Ultrasound for Estimation of Right Atrial Pressure. Am J Cardiol. 2007;99(Ivcci):1614-1616.

3. Schefold JC, Storm C, Bercker S, et al. Inferior Vena Cava Diameter Correlates with Invasive Hemodynamic Measures in Mechanically Ventilated Intensive Care Unit Patients with Sepsis. J Emerg Med. 2010;38(5):632-637.

4. Lucas BP, Candotti C, Margeta B, et al. Diagnostic accuracy of hospitalist-performed hand-carried ultrasound echocardiography after a brief training program. J Hosp Med. 2009;4(6):340-349.

5. Kory P. Rebuttal From Dr Kory. Chest. 2017;151(3):537-538.

6. Kory P. COUNTERPOINT: Should Acute Fluid Resuscitation Be Guided Primarily by Inferior Vena Cava Ultrasound for Patients in Shock? No. Chest. 2017;151(3):533-536.

7. Schmidt GA. Point: “Should acute fluid resuscitation be guided primarily by inferior vena caval ultrasound for patients in shock?” Yes. Chest. 2016.

8. Schmidt GA. Rebuttal From Dr Schmidt. Chest. 2017;151(3):536-537.

9. Blanco P, Volpicelli G. Common pitfalls in point-of-care ultrasound: a practical guide for emergency and critical care physicians. Crit Ultrasound J. 2016;8.

10. Via G, Tavazzi G, Price S. Ten situations where inferior vena cava ultrasound may fail to accurately predict fluid responsiveness: a physiologically based point of view. Intensive Care Med.

11. Barbier C, Loubières Y, Schmit C, et al. Respiratory changes in inferior vena cava diameter are helpful in predicting fluid responsiveness in ventilated septic patients. Intensive Care Med. 2004;30:1740-1746.

12. Feissel M, Michard F, Faller JP, Teboul JL. The respiratory variation in inferior vena cava diameter as a guide to fluid therapy. Intensive Care Med. 2004;30:1834-1837.