The IVC is measured about 2 cm from the entrance into the right atrium of the heart. Using M-mode, both inspiratory and expiratory diameters are measured. This patient has almost complete collapse of his IVC with respiration. His expiratory diameter is 1.63cm and his inspiratory diameter is 0.67cm. With this information, we look at the caval index chart below:
His caval index is 59%, which correlates to a CVP of 5-10mmHg and he is therfore under volume rescitated. He will need more IVF.Caval Index Evaluation in the Ventilated Patient
Just a reminder that the IVC diameter chart is for spontaneously breathing, non-vented patients. If you want to measure IVC diamter in ventilated patients, you must remember that due to the positive pressure ventilkation, the IVC will be the largest diameter with inhalation. Therefore, you should measure the IVC when the patient is sedated and not spontaneously breathing. Once you obtain the inspiratory and expiratory diameter, you must then plug it in to the following formula:
Inspiratory diameter- expiratory diameter/ expiratory diameter
If the answer is >18%, then the patient is still dry and needs IVF.
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