Inferior vena cava evaluation in fluid therapy decision making in intensive care: practical implications

Figure 1. Frank-Starling curve and its relationship with inferior vena cava variation among patients under invasive mechanical ventilation. The relationship between preload and systolic volume: Frank-Starling curve. This figure shows the expected increase in systolic volume after the administration of fluids, which depends on cardiac function and the initial preload. For the same amount of fluids administered and for a similar initial preload, the variation in the resulting systolic volume depends on the cardiac function: (A) The Frank-Starling curve of a patient with normal cardiac function. In patients with normal cardiac function, the results of fluid administration only depend on the initial preload: If it is low (rising phase of the curve), then systolic volume significantly increases (≥ 10 - 15%, respondent patient), corresponding to a significant variation in the diameter of the inferior vena cava with the application of positive pressure to the thorax during inspiration in the ventilated patient; if it is elevated (flat phase of the curve), then no significant increase in systolic volume is observed (<10 - 15%, nonrespondent) leading to pulmonary overload, which corresponds to an…

Figure 2. Inferior vena cava diameter measurement technique. The inferior vena cava should be measured in two-dimensional mode at the subcostal window using the long axis distal to the hepatic vein (arrow), approximately 1 - 3cm from the entrance of the inferior vena cava in the right atrium (A). Measurements near the right atrium entrance or near the diaphragm should be avoided. Its diameter can also be measured in M mode simultaneously with the two-dimensional mode to ensure the perfect alignment of the probe, perpendicular to the long axis of the inferior vena cava. In patients under invasive mechanical ventilation, the diameter of the inferior vena cava at the end of inspiration (maximal diameter) and at the end of expiration (minimum diameter) is measured to calculate the distensibility index. The probe must be kept in a fixed position during the respiratory cycle. Image obtained with a GE Vivid T8 echocardiograph. IVC - inferior vena cava.

Figure 3. Formulas for calculating the distensibility index of the inferior vena cava. DI - distensibility index; Dmax - maximum diameter; Dmin - minimum diameter; IVC - inferior vena cava.