Study: NCT06180902

Intervention type: DIAGNOSTIC_TEST
Group type: EXPERIMENTAL
Intervention: Inferior vena cava's diameter ratio
Description: In mechanical ventilation, the Inferior Vena Cava's maximum diameter (IVCmax) is measured at peak inspiration, and minimum diameter (IVCmin) at expiration's end. The Distensibility Index (IVCDI) is calculated as \[(IVCmax - IVCmin) / IVCmin\] × 100%. In spontaneous breathing, IVCmax is the diameter at expiration's end, and IVCmin at inspiration's end. The Collapse Index (IVCCI) is \[(IVCmax - IVCmin) / IVCmax\] × 100%.~Clinically, an IVCDI/IVCCI ≥ 18% indicates a 'responder'. Values \< 18% denote 'non-responders'.

Intervention type: DIAGNOSTIC_TEST
Group type: EXPERIMENTAL
Intervention: Central venous pressure
Description: In our protocol, patients lie flat, connected to a saline-filled system for intravenous infusion via a central venous catheter. The system, starting from the subclavian catheter, extends to the 2nd to 3rd intercostal space at the mid-axillary line. The tube's end is raised perpendicular to the bed until saline flow stops, marking the liquid level. The height from the mid-axillary line to this point is measured in millimeters. If the liquid column falls below the mid-axillary line, indicating continuous flow, the CVP is negative, and the catheter is closed to block air entry. CVP readings are taken at exhalation's end.~CVP interpretation:~* CVP ≤ 12 mmHg (16.3 cm H2O) indicates a responder.~* CVP \> 12 mmHg (16.3 cm H2O) indicates a non-responder.

Intervention type: DIAGNOSTIC_TEST
Group type: EXPERIMENTAL
Intervention: Passive leg raising test
Description: In our protocol, the patient starts flat for initial CVP measurement. Then, the bed is tilted to 45 degrees for the first measurements: Systolic/Diastolic Blood Pressure, Mean Arterial Pressure, and Pulse Pressure (Systolic - Diastolic). Next, the bed is adjusted to elevate the feet, creating a 135-degree angle between torso and legs. After 90 seconds, the second set of measurements, including CVP, is taken. The patient is then returned to the initial position.~Interpreting results:~A responder is indicated by:~* Over 10% Pulse Pressure (PP) increase in the second measurement;~* The ratio of PP change to CVP change (∆PP / ∆CVP) \> 1;~* Second measurement CVP ≤ 12 mmHg (16.3 cm H2O).~A non-responder is indicated by the presence at least one of the following:~* Less than 10% PP increase in the second measurement;~* The ratio of PP change to CVP change (∆PP / ∆CVP) ≤ 1;~* Second measurement CVP \> 12 mmHg (16.3 cm H2O).

Intervention type: DIAGNOSTIC_TEST
Group type: EXPERIMENTAL
Intervention: Fluid challenge
Description: In our clinical procedure, patients start horizontally for initial measurements: Systolic, Diastolic, Mean Arterial, Pulse Blood Pressures, and Central Venous Pressure (CVP). Then, they receive a balanced crystalloid solution at 4 ml/kg body weight at maximum permissible infusion rate. After infusion, a second measurement set identical to the first is taken.~Interpretation:~A responder is indicated by:~* Pulse Pressure (PP) increase \> 10% in second measurement;~* Ratio of PP change to CVP change (∆PP / ∆CVP) \> 1;~* Second CVP measurement ≤ 12 mmHg (16.3 cm H2O).~A non-responder is indicated by the presence at least one of the following:~* PP increase \< 10% in second measurement;~* Ratio of PP change to CVP change (∆PP / ∆CVP) ≤ 1;~* Second CVP measurement \> 12 mmHg (16.3 cm H2O).

Intervention type: PROCEDURE
Group type: EXPERIMENTAL
Intervention: Fluid infusion
Description: After assessing infusion therapy responsiveness, patients receive balanced crystalloid solutions at 1000 ml, infused at 15 ml/kg/hour, accounting for any prior infusions. Effectiveness evaluation follows, involving cardiac output reassessment (initially measured upon study enrollment). Effectiveness is determined by a ≥10% increase in cardiac output in the second measurement compared to the first. This is quantified as: \[(CO(after) - CO(before)) / CO(before)\] × 100% ≥ 10%, where CO(after) is the post-infusion cardiac output and CO(before) the pre-infusion output.