Although fluid therapy is the fundamental method for the management of critically hypotensive patients, the exact assessment of volume status (VS) is not easy. SVV or PPV needs arterial catherization. Non-invasive methods such as pulse oximeter plethysmography, impedance plethysmography or impedance phlebography require specific device and its’ accuracy is still questionable. Ultrasound is widely used in many medical fields. One of the advantages of using ultrasound is that it provides real-time results, contrary to other radiologic tests. The technique for examination is also simple that nonphysician can perform. Measuring DCIIVC and evaluating VS of the patients is much easier.3,6 DCIIVC shows very high potential as a tool for point-of-care. DCIIVC has been introduced as a useful tool of measuring VS in rapid ultrasound in shock (RUSH) for the evaluation of critically ill patients.7 DCIIVC is used for the real-time monitoring of fluid removal during continuous renal replacement therapy and fluid therapy for heart failure.4,8,9,10 The qualitative assessment of DCIIVC has also been carried out in a prospective study and demonstrated that DCIIVC offers a rapid, non-invasive way to evaluate VS in critically ill patients.11 Despite its accuracy and usefulness, DCIIVC is not widely used as a clinical indicator for FR.
There are several reasons. One of them is that the usefulness of DCIIVC is debatable. DCIIVC is known to reflect VS well. The IVC diameter can be used as a point-of-care to guide heart failure (FH) management. In acute HF syndrome, CIIVC ≥ 0.5 on admission suggests a volume shift from the central vein into the pulmonary vasculature and is helpful in diuretic use.12 However, some studies had negative conclusions about the metrics of IVC. The IVC diameter checked on computed tomography was not a good indicator of VS in hemodynamically normal trauma patients.13 Even meta-analysis has different results. Two meta-analyses showed that DCIIVC is a reliable parameter for hypovolemia and has a great value in predicting fluid responsiveness.14,15 However, other meta-analyses on DCIIVC concluded that it is not a reliable method to predict fluid responsiveness.16,17 Hence, the effectiveness of DCIIVC to predict VS or fluid responsiveness has not yet reached a conclusion.
We wanted to clarify the effectiveness of DCIIVC as clinical indicator for FR by retrospective analysis. The uniqueness of this study is the evaluation of the clinical outcomes of DCIIVC, contrary to a previous study that evaluated the accuracy for fluid responsiveness or correlation with hypovolemia or lactate levels. These parameters do not always agree with the clinical outcomes. Moreover, previous studies have evaluated mainly medical patients with cardiac or renal concerns. This study included surgical patients. Usually, hypotension of surgical patients is caused by bleeding, hypovolemia or septic condition due to acute insult. Because their previous hemodynamic function was normal, meticulous control of FR will result in favorable recovery. The results of this study showed that using DCIIVC as the indicator for FR made physician use lesser fluid than using CVP, lactate or patient’s weight with similar hemodynamic recovery and clinical outcomes. DCIIVC can be a useful guide of point-of-care for fluid therapy in shock patients requiring strict volume control.
DCIIVC-guided FR failed to improve clinical outcomes in this study. We believe this is because of the diverse characters of the patients. The cause of hypotension was variable. Some patients had hypovolemia, but other had sepsis or brain death. DCIIVC needs to be evaluated in the same disease group in a future prospective study.
We used the IVC of the hepatic vein inlet as the location of examination. DCIIVC can be measured at the level of the renal vein or junction of the hepatic inlet. Compared to the IVC at the level of the renal vein, the IVC at the hepatic vein inlet is much easier to find and can be checked during Focused Assessment with Sonography in Trauma. If we check the IVC near the heart, the chance of failure is very low, but this location does not show equivalent results and is not recommended.18
This study has some limitations. The study is an analysis of two different periods and the strength of evidence is very weak. We checked the anteroposterior diameter of the IVC. A previous study recommended not to measure DCIIVC in the vertical direction because true collapse of the vessel does not occur in the vertical direction.19