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Septic Shock and Awe with Caval Index!

Case: 72-year-old woman is brought in by EMS for altered mental status. In the field she is diaphoretic, tachycardic, and tachypneic. She gets to the ED and is able to tell you her name and birthdate, but can’t say where she is or what happened. She has crackles and wheezing in the right lower lobe. Her initial blood pressure is 82/59 and she has weak distal pulses. The team’s main concern is septic shock. Fluids are started, but after the first liter her vitals are unchanged. Since she has not responded to initial fluid challenge, you question the best next steps in her resuscitation.

Clinical Question: In the ED, what tests can be used to measure volume status and predict fluid responsiveness in patients who present with shock?

Summary of evidence:

  • Only about half of patients who present in shock will adequately respond to fluids. Determining fluid responsiveness early during resuscitation aids in optimizing cardiac output. (4, 6)

  • Central venous pressure (CVP) is one widely used indicator of volume status. It is the mainstay of hemodynamic monitoring in the ICU for critically ill patients. (1)

  • However, CVP measurement requires central venous catheterization, which carries its own risks. Furthermore, CVP is not always accurate, and its use has not consistently been shown to provide mortality benefits. (3, 4)

  • In the ED, it is not always feasible or appropriate to place central lines for patients in shock. Quicker, non-invasive options have been gaining favor, and caval index is one that is frequently used. (5, 6)

  • Caval index (%) = IVC expiratory diameter – IVC inspiratory diameter

IVC inspiratory diameter

  • A high caval index means the IVC totally collapses, suggesting low blood volume.

  • A low caval index means the IVC does not collapse, suggesting volume overload. (2)

  • A caval index of >50% correlates with CVP <8 with sensitivity 91%, specificity 94%, PPV 87%, NPV 96%, showing that caval index is as good as CVP, but without many of the negatives of an invasive procedure. (2, 7 )

  • Caval index can be measured by most clinicians and the results can be available in just a few minutes. (1, 5)


  • In the emergency department using the caval index is an acceptable way to quickly assess fluid status and measure response to fluid challenge.

  • Although IVC sonography is generally easy to perform, accurate measurements depend on the experience of the examiner.

  • In certain populations (i.e. athletes, mechanically ventilated patients) IVC collapsibility may not be an acceptable estimation of CVP.

  • Click here for an ACEP article on how to perform the ultrasound


  1. Bendjelid K, Romand JA. Fluid responsiveness in mechanically ventilated patients: a review of indices used in intensive care. Intensive care medicine. 2003; 29(3): 352–60

  2. Ciozda W, Kenda I, Kehl DW, Zimmer R, Khandwalla R, Kimchi A. The efficacy of sonographic measurement of inferior vena cava diameter as an estimate of central venous pressure. Cardiovascular Ultrasound. 2016;14:33

  3. Kumar, A, Anel R, Bunnell E, et al. Pulmonary artery occlusion pressure and central venous pressure fail to predict ventricular filling volume, cardiac performance, or the response to volume infusion in normal subjects. Critical Care Medicine. 2004;32:691-699

  4. Lu N, Xiuming X, Jiang L, Yang D, Yin K. Exploring the best predictors of fluid responsiveness in patients with septic shock. American Journal of Emergency Medicine. 2017;35:1258-1265

  5. Marik PE, Baram M. Noninvasive hemodynamic monitoring in the intensive care unit. Critical Care Clinics. 2007; 23:383-400

  6. Schefold J, Storm C, Bercker S, et al. Inferior vena cava diameter correlates with invasive hemodynamic measures in mechanically ventilated intensive care unit patients with sepsis. The Journal of Emergency Medicine. 2010;(38)5:632-637

  7. Stawicki SP, Braslow BM, Panebianco NL et al. Intensivist use of hand-carried ultrasonography to measure IVC collapsibility in estimating intravascular volume status: correlations with CVP. J Am Coll Surg. 2009;209:55-61