The main finding of the present study is that a mini-fluid challenge (150 ml of albumin 5%) is sufficient to assess fluid responsiveness in patients with Child A cirrhosis but not Child B or C cirrhosis.
We found that a SV change > 10% during mini-fluid challenge following liver transplant asess fluid responsiveness in Child A cirrhosis patients with 70% sensitivity and 100% specificity. To the best of our knowledge, this is the first study to investigate mini-fluid challenge testing in patients with ESLD. Patients with ESLD not only have an abnormally high blood volume, but also an abnormal blood volume distribution. However, not all patients with ESLD exhibit the same response to changes in blood volume. Healthy individuals and patients with Child A cirrhosis differ in their response to blood volume expansion compared to patients with Child B and C cirrhosis. Volume expansion resulted in significantly increased central blood volume in patients with Child A cirrhosis compared to patients with Child B or C cirrhosis,  which may explain the difference in patient response to mini-fluid challenge observed in the present study. The plausible mechanism of this finding was that patients with Child A have less severe alteration in vasomotor and venous capicitance compared to Child B and C . Thus, mini fluid bolus (150 mL) could increase the mean systemic filling pressure in patients with Child A but not in patients with Child B or C.
In the early stages of our liver transplant program, we typically extubated the patient 6–8 h after admission to the ICU . However, we changed our protocol 8 years ago and more than 90% of patients are now extubated successfully inside the operating room. This makes the assessment of fluid responsiveness difficult because all dynamic indices, including pulse pressure variation and stroke volume variation, are unreliable during spontaneous breathing. Mini-fluid challenge and passive leg raising remain the only available tests for spontaneously breathing patients.
There is currently great interest in using fluid responsiveness as determined by mini-fluid challenge to guide transfusion, particularly to avoid volume overloading. While several studies have tested the concept of mini-fluid challenge, these investigations used different volumes and fluid types [7, 11, 12]. In the first such study, Muller et al. investigated the validity of mini-fluid challenge among 39 critically ill ventilated patients with acute circulatory failure and found that an increase in aortic blood flow ≥10% after rapid infusion of 100 ml hydroxyethyl starch predicted fluid responsiveness.7 More recently, Aya et al. found that 4 ml/kg was the minimum volume required to evoke a significant hemodynamic effect . Smorenberg et al. reported that 150 ml of hydroxyethyl starch reliably predicted fluid responsiveness after cardiac surgery . In our study, we used the same volume (150 ml) of albumin 5% and found this amount to be effective only in patients with Child A cirrhosis. Thus, a higher-volume mini-fluid challenge may be required for patients with advanced cirrhosis.
The concept of using predefined criteria for increase of CO after fluid challenge to differentiate between responder and non-responder depends on the starling mechanism. However, it is worth mentioning that CO changes during fluid bolus is affected not only by preload but also by afterload. Rapid fluid infusion decrease systemic vascular resistance by hemodilution. One study found that infusion of 1 l of colloid caused 20% increase in blood volume, 20% decrease in hemoglobin, and 40% increase in CO . The increase in CO in their study is probably due to not only an increase in preload but also a decrease in afterload.
In our study, we defined fluid responsiveness as an increase in SV by 15% after infusion of 500 ml albumin 5%. Despite that the concept of fluid responsiveness has been emerged 20 years ago, there are still considerable variabilities in the definition, implementation, and assessment of fluid challenge. Recent systematic review found that 60% of the studies defined fluid responsiveness as an increase of ≥15% of CI or CO immediately after fluid challenge .
Albumin 5% infusion was chosen to test fluid responsiveness instead of hydroxyethyl starch because we have previously shown that this solution is as effective for volume expansion . Moreover, the safety of hydroxyethyl starch has been questioned and we have abandoned its use in the postoperative period .
Our study had several limitations. First, all our patients had excellent cardiac function during the early. Postoperative period, so we cannot extrapolate our findings to patients with poor cardiac function. Second, assessment of minifluid using echocardiography is challenging because the minifluid challenge induces small changes in cardiac output which may miss some true responders, however, we used single operator to limit the effect of interobserver variability.