In assessing critically ill patients, an accurate assessment of a patient's volume status and whether they will respond to a fluid challenge with an increase in cardiac output is vital. 1 When hypovolemia is detected, volume expansion is utilized to enhance hemodynamics and restore normal blood pressure. 2 Hemodynamic tests (right atrial pressure, pulmonary artery occlusion pressure, and cardiac output ) are used to assess preload in critically ill patients, although these indexes are not necessarily reliable predictors of fluid status. According to the Starling law, fluid administration is hypothesized to boost cardiac output by raising preload, which describes a positive relationship between cardiac muscle fiber length and contractility. However, the Starling curve hits a plateau beyond its ascending leg, and additional fluid administration can be hazardous, leading to right ventricular overload and pulmonary edema Invasive or noninvasive techniques can be used to determine blood volume status. Assessments such as central venous pressure (CVP) and mean pulmonary artery pressure (mPAP) are both invasive procedures. Various factors influence CVP (including thoracic, pericardial, abdominal pressures, etc.). CVP can be used as a fluid management indication, although It can be misused to estimate blood volume or mislead methods for treatment. Dynamic indices such as stroke volume variation (SVV) and pulse pressure variation (PPV) are superior to static indices for assessing volume status. However, these dynamic indices are unreliable when a patient is ventilated with low tidal volume, such as acute respiratory distress syndrome (ARDS); the tidal volume is insufficient to change intrathoracic pressure significantly. Ultrasound (US) evaluation of the inferior vena cava (IVC) may help determine fluid status.
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Timeframe: the first 48 hours postoperative