Study: NCT05968040

Intervention type: PROCEDURE
Group type: ACTIVE_COMPARATOR
Intervention: Inferior vena cava diameter measurement by ultrasonography
Description: The diameter of the inferior vena cava will be measured at 2 cm close to the entrance of the right atrium. Ultrasound images will be taken at the end of inspiration (Dmax) and at the end expiration (Dmin) to calculate the inferior vena cava dispensability index (dIVC), and will be recorded before and after fluid challenge test of 5 ml/kg crystalloid within 15 min. The IVC distensibility index (IVC-DI) will be calculated using the formula: IVC-DI = IVCmax - IVCmin/ IVCmin. The indices will be expressed as a percentage.

Intervention type: PROCEDURE
Group type: ACTIVE_COMPARATOR
Intervention: Inferior vena cava diameter measurement by ultrasonography
Description: The diameter of the inferior vena cava will be measured at 2 cm close to the entrance of the right atrium. Ultrasound images will be taken at the end of inspiration (Dmax) and at the end expiration (Dmin) to calculate the inferior vena cava dispensability index (dIVC), and will be recorded before and after fluid challenge test of 5 ml/kg crystalloid within 15 min. The IVC distensibility index (IVC-DI) will be calculated using the formula: IVC-DI = IVCmax - IVCmin/ IVCmin. The indices will be expressed as a percentage.

Intervention type: PROCEDURE
Group type: ACTIVE_COMPARATOR
Intervention: difference between peak velocities of carotid artery by ultrasound
Description: Carotid ultrasound images will be obtained from the left CCA in both short-axis and long-axis views by experienced sonographers. The patient will be in supine position, with the head rotated slightly to the right. A broadband linear array transducer 12-4 MHz and the short-axis view will be used for orientation and identification of the CCA. Next, in the long-axis view, Peak Waveform Doppler signals will be acquired by placing a 0.5 mm calliper at the center of the vessel and parallel to the vessel walls, approximately 2 cm proximal from the carotid bifurcation. Insonation-angles between the ultrasound beam and blood flow will be maintained.~ΔVpeakCCA = (MaxCDPV-MinCDPV)+(MaxCDPV+MinCDPV)x100

Intervention type: PROCEDURE
Group type: ACTIVE_COMPARATOR
Intervention: difference between peak velocities of carotid artery by ultrasound
Description: Carotid ultrasound images will be obtained from the left CCA in both short-axis and long-axis views by experienced sonographers. The patient will be in supine position, with the head rotated slightly to the right. A broadband linear array transducer 12-4 MHz and the short-axis view will be used for orientation and identification of the CCA. Next, in the long-axis view, Peak Waveform Doppler signals will be acquired by placing a 0.5 mm calliper at the center of the vessel and parallel to the vessel walls, approximately 2 cm proximal from the carotid bifurcation. Insonation-angles between the ultrasound beam and blood flow will be maintained.~ΔVpeakCCA = (MaxCDPV-MinCDPV)+(MaxCDPV+MinCDPV)x100

Intervention type: PROCEDURE
Group type: ACTIVE_COMPARATOR
Intervention: cardiac output be transthoracic echocardiography
Description: CO will be recorded as baseline measure and after fluid administration. If CO increased more than 15%, it will be considered fluid responder. Increase in cardiac output = (cardiac output after first fluid challenge - cardiac output before)/cardiac output before) X 100.~TTE will be used to measure LTOT and VTI x HR.

Intervention type: PROCEDURE
Group type: ACTIVE_COMPARATOR
Intervention: cardiac output be transthoracic echocardiography
Description: CO will be recorded as baseline measure and after fluid administration. If CO increased more than 15%, it will be considered fluid responder. Increase in cardiac output = (cardiac output after first fluid challenge - cardiac output before)/cardiac output before) X 100.~TTE will be used to measure LTOT and VTI x HR.