Measurements of Fluid Requirements with Cardiovascular Challenges

Fluid administration is the first-line treatment in most cases of acute circulatory failure. However, this treatment poses two problems. The first is that it leads inconsistently to the increase in cardiac output that was expected. The second problem is that excessive fluid administration, which leads to increased fluid balance, worsens the prognosis of critically ill patients. Thus, apart from obvious fluid losses, hypovolemic shock state or the initial phase of the septic shock state, it appears logical to predict before infusing fluid that it will increase cardiac output static markers of cardiac preload, such as central venous pressure, are ineffective for this purpose, and several dynamic tests or indices have been developed. Changes in arterial pulse pressure or the diameter of the inferior and superior venae cavae in mechanically ventilated patients suffer from very strict conditions of use. The passive leg raising test and the respiratory occlusion tests act as internal preload tests and have broader indications. They must be performed by directly measuring the cardiac output. For optimal use, clinicians should be aware of the indications, contraindications, and limitations of these tests as well as how to perform them.