Evaluación ecográfica de la vena cava inferior en los pacientes hemodinámicamente inestables

Abstract

An ultrasound technique is presented for assessing the respiratory variation of the diameter of the inferior vena cava (IVC) in ventilated and haemodynamically unstable patients, as well as to demonstrate its usefulness as a therapeutic choice. In healthy patients, changes in intrathoracic pressure are transmitted to the IVC, reducing the vessel diameter by 50%. In mechanically ventilated patients, the inspiratory phase produces an increase in pleural pressure that decreases venous return. Therefore the changes in vessel diameter are reversed, with an inspiratory increase and an expiratory decrease. Significant variation during inspiration is useful to differentiate patients that are likely responders to fluid replacement therapy.A sagittal ultrasound was performed on the inferior vena cava at subxiphoid level. It was performed with the cursor in M mode at 3cm from the right atrium, generating a graphics of the vein diameter versus time. The patient must be sedated, ventilated (volume 8-10ml/kg), with a respiratory rate of 16 cycles/minutes, and 0° inclination. The maximum and minimum diameters were recorded during the respiratory cycle and the percentage change was calculated using the following formula: diameter (D) maximum IVC-D min/D max. A variation is considered significant when ≥ 12%.The ultrasound technique used to measure variability of the vena cava allows being able to select ventilated haemodynamically unstable patients who will respond to fluid replacement therapy, being those who exhibit a variation in the calibre of the IVC of more than 12%.