Measurements. The diameter of the IVC for calculation of the caval index should be measured 2 cm from where it enters the right atrium (Figures 1, 2, and 3).

An alternative way to visualize respiratory variation is to use M-mode, with the beam overlying the IVC 2 cm from the right atrium.

The inspiratory and expiratory diameter can then be measured on the M-mode image, at the smallest and largest locations, respectively (Figures 4 and 5).

Findings

• Volume depletion. In these patients, the diameter of the IVC will be decreased and the percentage collapse will be greater than 50%. With complete collapse, the IVC may become difficult to visualize (Figure 6).
• Volume overload. Patients with increased intravascular volume will have a large IVC diameter and minimal collapse on inspiration (Figure 7). In severe cases, there may not be any notable respiratory variation seen in M-mode.

References

• ACEP Policy Statement on Emergency Ultrasound Guidelines. Ann. Emerg. Med. 2009;53:550-70.
• Blehar DJ, Dickman E, Gaspari R. Identification of congestive heart failure via respiratory variation of inferior vena cava diameter. Am. J. Emerg. Med. 2009;27:71-5.
• Chen L, Santucci KA, Kim Y. Use of ultrasound measurement of the inferior vena cava diameter as an objective tool in the assessment of children with clinical dehydration. Acad. Emerg. Med. 2007:14:841-5.
• Feissel M, Michard F, Faller JP, et al. The respiratory variation in inferior vena cava diameter as a guide to fluid therapy. Intensive Care Med. 2004;30:1834-7.
• Fields JM, Lee PA, Jenq KY, et al. The interrater reliability of inferior vena cava ultrasound by bedside clinician sonographers in emergency department patients. Acad. Emerg. Med. 2011;18:98-101.
• Kircher BJ, Himelman RB, Schiller NB. Noninvasive estimation of right atrial pressure from the inspiratory collapse of the inferior vena cava. Am J. Cardiol. 1990;66:493-6.
• Kosiak W, Swieton D, Piskunowicz M. Sonographic inferior vena cava/aorta diameter index, a new approach to the body fluid status assessment in children and young adults in emergency ultrasound preliminary study. Acad. J. Emerg. Med. 2008;26:320-5.
• Nagdev AD, Merchant RC, Tirado-Gonzalez A, et al. Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure. Ann. Emerg. Med. 2010;55:290-5.
• Randazzo MR, Snoey ER, Levitt MA, et al. Accuracy of emergency physician assessment of left ventricular ejection fraction and central venous pressure using echocardiography. Acad. Emerg. Med. 2003;10:973-7.

Contributor Disclosures

Contributors

All of the authors are attending physicians in the department of emergency medicine at St. Luke’s–Roosevelt Hospital in New York. Dr. Goldflam is the emergency ultrasound fellow, Dr. Lewiss is director of the emergency ultrasound division, and Dr. Saul is the division’s fellowship director. Medical Editor Dr. Robert C. Solomon is an attending emergency physician at Southwest Regional Medical Center in Waynesburg, Pa., and clinical assistant professor of emergency medicine at the West Virginia School of Osteopathic Medicine, Lewisburg.