Ultrasound Evaluation of Fluid Tolerance and Fluid Responsiveness in Postoperative Cardiac Surgery Patients

Postoperative management following cardiac surgery requires the integration of multiple clinical and hemodynamic variables to guide individualized treatment. Important therapeutic decisions include intravenous fluid administration, fluid removal with diuretics, and the use of vasoactive and inotropic medications. Point-of-care ultrasound (POCUS) may provide complementary physiologic information to support these decisions by assessing both fluid tolerance and fluid responsiveness.

Fluid tolerance refers to the ability of a patient to receive additional fluid without developing or worsening clinically significant congestion. The Venous Excess UltraSound (VExUS) score is an ultrasound-based approach to evaluating systemic venous congestion. Abnormal VExUS findings have been associated with adverse outcomes following cardiac surgery; however, whether incorporating VExUS into clinical decision-making can meaningfully influence management remains uncertain.

Fluid responsiveness refers to the capacity of cardiac output to increase following an increase in cardiac preload. Dynamic ultrasound-based assessments can be used to evaluate fluid responsiveness and may help identify patients who are more likely to benefit from fluid administration. Combining assessments of fluid tolerance and fluid responsiveness may therefore provide complementary information: identifying patients who may benefit from additional fluid while also identifying those at risk of adverse effects from fluid accumulation.

USE-the-FORCE-in-Cardiovascular ICU (UTF-in-CVICU) is a pilot randomized controlled trial evaluating a structured POCUS-based assessment of fluid tolerance and fluid responsiveness in adult patients following cardiac surgery. Participants will be randomized to an intervention group or a standard-care group. In the intervention group, a structured ultrasound assessment will be performed and the results will be communicated to the treating team. The ultrasound evaluation includes assessment of venous congestion using VExUS and assessment of fluid responsiveness. The treating physician will retain responsibility for all therapeutic decisions and will determine whether the ultrasound findings warrant a modification of the management plan. Participants randomized to the control group will receive standard postoperative care.

The trial has two co-primary objectives. The proof-of-concept objective is to determine how frequently information obtained from the ultrasound assessment leads the treating physician to modify the planned management strategy. The feasibility objective is to determine whether the study procedures can be successfully completed according to protocol, including completion of the ultrasound assessments and timely communication of the report to the treating team.

Secondary and exploratory objectives will evaluate differences between groups in fluid balance and the use of diuretics, inotropes, and pulmonary vasodilators during the first 72 hours following randomization. Kidney outcomes will include the occurrence of acute kidney injury and changes in estimated glomerular filtration rate. Additional exploratory clinical outcomes include duration of vasopressor therapy, duration of mechanical ventilation, intensive care unit and hospital length of stay, cumulative time in perioperative organ dysfunction or death, kidney replacement therapy, and operative mortality. Qualitative feedback from treating physicians regarding the ultrasound assessment will also be evaluated.

Inclusion criteria

• Adults aged ≥18 years
• Undergoing planned cardiac surgery with anticipated postoperative admission to the intensive care unit

Exclusion criteria

• Known stage 5 chronic kidney disease according to the KDIGO classification (eGFR less than 15 mL/min/1.73m2) or on renal replacement therapy
• Planned or ongoing mechanical circulatory support
• Planned or history of heart transplantation