The IVC is a beautiful thing; it returns blood to the heart from all over the body, and without that, we would die – truly is the gift that keeps on giving. It gives so much information about a patient as it gets affected by so many disease processes:
IVC dilation (hypervolemic)- tamponade, PE, CHF exacerbation, severe mitral regurgitation or aortic stenosis, significant renal failure, severe COPD/Cor Pulmonale
IVC collapsed (hypovolemic) – septic shock, hypovolemic shock, dehydration
Now lets talk technique: Using the low frequency/cardiac phased array probe, start by visualizing the 4-chamber heart in subxiphoid view then rotate your probe 90 degrees so that the indicator is toward the head (cardiologists will do this with an image that looks flipped – but that’s ok – tomAto, tomahto). You will be in the longitudinal view of the IVC. The degree of head of bed elevation has not been shown to make a significant difference.
You MUST (yes, all caps on purpose here) see the IVC enter the right atrium. That is the only clear way to differentiate it from the aorta which is parallel to and right next to the IVC. You may even need to slide your probe toward the patient’s right side, or angle your probe in that direction, to get a better view of the IVC, visualizing it in its largest diameter section. For calculation, you measure the IVC diameter 2-3 cm from the entrance into the right atrium (usually this is where the hepatic vein enters the IVC). Make sure to also visualize the IVC during normal respiration. Serial IVC scans can help manage the volume needs of a chock patient.
Estimated CVP correlation with IVC measurement:
CVP < 5 IVC < 1.5 cm with > 50% resp variation
CVP = 5-10 IVC = 1.5-2.5 cm with > 50% resp variation
CVP = 10-15 IVC = 1.5-2.5 cm with < 50% resp variation
CVP = 15-20 IVC > 2.5 cm with < 50% resp variation
CVP > 20 IVC >2.5 cm with no respiratory variation
(IVC expiratory diameter – IVC inspiratory diameter)/IVC expiratory diameter × 100 = caval index (%). The caval index is written as a percentage, where a number close to 100% is indicative of almost complete collapse (and therefore volume depletion).
Thanks to my critical care friends at Stanford, namely Dr. Anne-Sophie Beraud, for this table to help differentiate the IVC from the aorta. A figure of the IVC during respiration (and with positive pressure ventilation) is right below it – you’ll notice that the IVC variation inverts with pos-press-vent: