The goal of this clinical trial is to determine whether common carotid artery blood flow measured by bedside Doppler ultrasound can accurately identify fluid responsiveness in mechanically ventilated adults with sepsis. The study will compare this method with transthoracic echocardiography-derived cardiac output, which is a commonly used non-invasive technique for assessing hemodynamic status in critically ill patients. The study also aims to evaluate whether carotid artery ultrasound can provide a faster and more practical bedside assessment during fluid resuscitation in the intensive care unit.

In patients with sepsis, giving too little intravenous fluid may worsen organ perfusion and shock, while excessive fluid administration may lead to complications such as pulmonary edema, worsening oxygenation, prolonged mechanical ventilation, and longer intensive care unit stay. Because of this, clinicians need reliable methods to identify which patients are likely to benefit from fluid administration. This concept is known as fluid responsiveness.

The main questions this study aims to answer are:

• Can common carotid artery blood flow measured by ultrasound predict fluid responsiveness as accurately as transthoracic echocardiography-derived cardiac output?
• How closely do changes in carotid artery blood flow correspond to changes in cardiac output during passive leg raising?
• Can carotid ultrasound provide a quicker and simpler bedside method for assessing fluid responsiveness in critically ill patients receiving mechanical ventilation? Researchers will compare two ultrasound-based methods during a passive leg raising test. Passive leg raising is a temporary bedside maneuver used to simulate a fluid challenge without immediately giving intravenous fluids. During this maneuver, the patient's legs are elevated while the upper body is lowered, allowing blood from the lower limbs to temporarily return to the central circulation. This increases blood flow to the heart and may increase cardiac output in patients who are likely to respond to fluid administration.

The study team will first record baseline measurements of common carotid artery blood flow and transthoracic echocardiographic cardiac output while the patient is in a semi-recumbent position. The passive leg raising maneuver will then be performed, and both measurements will be repeated to evaluate changes in blood flow and cardiac output. If the predefined criteria for fluid responsiveness are met, the participant will receive intravenous crystalloid fluid according to the study protocol.

Participants will:

• Undergo bedside Doppler ultrasound measurement of common carotid artery blood flow
• Undergo transthoracic echocardiography to measure cardiac output
• Have ultrasound measurements recorded before and after passive leg raising
• Receive intravenous fluid administration if fluid responsiveness criteria are met
• Continue routine monitoring of blood pressure, heart rate, oxygenation, urine output, and other intensive care parameters during the study period The findings from this study may help determine whether carotid artery ultrasound can be used as a practical bedside tool for fluid assessment in mechanically ventilated patients with sepsis, particularly in settings where rapid and non-invasive monitoring is needed.

This study is being conducted in the intensive care unit to examine a non-invasive ultrasound-based approach for evaluating circulatory response in adults with sepsis who are receiving mechanical ventilation. The investigation focuses on whether Doppler assessment of blood flow in the common carotid artery can provide clinically useful information comparable to cardiac output measurements obtained through transthoracic echocardiography during bedside hemodynamic assessment.

Management of septic patients frequently requires decisions regarding intravenous fluid administration. Both insufficient and excessive fluid therapy may negatively affect patient outcomes. Reliable bedside techniques that identify patients who are likely to benefit from additional fluid remain an important component of critical care practice. Current hemodynamic assessment methods often require specialized expertise, repeated examinations, or technically challenging image acquisition in ventilated patients.

This trial will assess circulatory changes produced by a passive leg raising maneuver. Passive leg raising temporarily increases venous return by transferring blood from the lower limbs toward the thoracic circulation. The maneuver provides a reversible physiologic preload challenge that allows evaluation of cardiovascular response without initially administering intravenous fluid.

Participants enrolled in the study will undergo sequential ultrasound-based hemodynamic assessments performed by trained investigators. Measurements will first be obtained while the participant is positioned with the head elevated. The participant will then undergo passive leg raising with elevation of both lower limbs and adjustment of trunk position according to study protocol. Repeat hemodynamic measurements will be recorded during the maneuver.

For carotid Doppler evaluation, the common carotid artery will be visualized in longitudinal orientation using a high-frequency linear ultrasound probe. Vessel diameter and Doppler flow measurements will be obtained from a standardized location proximal to the carotid bulb. Flow estimation will be derived from Doppler velocity measurements combined with arterial diameter and heart rate.

Cardiac output assessment will be performed separately using transthoracic echocardiography and Doppler evaluation of flow across the left ventricular outflow tract. Measurements will be obtained using standardized echocardiographic views and procedural methods.

Participants who demonstrate predefined hemodynamic changes during assessment may receive crystalloid administration according to the study protocol. Additional measurements may then be performed to evaluate circulatory response after fluid administration.

The primary analysis will evaluate the diagnostic performance of carotid Doppler-derived flow assessment for identifying preload responsiveness in comparison with transthoracic echocardiographic measurements. Agreement between both methods and the ability of carotid Doppler assessment to identify clinically significant hemodynamic change will also be examined.

Additional analyses will assess bedside practicality, including the ease and duration of ultrasound assessment in critically ill ventilated patients. Technical factors affecting image acquisition and measurement reliability will also be documented during the study.

Clinical information and ultrasound findings will be entered into standardized study forms. Data review procedures will include consistency checks, verification of recorded values, and evaluation of incomplete or missing variables before statistical analysis. Statistical methods will include correlation analysis, agreement testing, and calculation of diagnostic performance measures using predefined study thresholds.

This investigation may provide further evidence regarding the role of carotid Doppler ultrasound as a rapid bedside technique for circulatory assessment in mechanically ventilated adults with sepsis managed in the intensive care unit.

Inclusion Criteria:

• • Adults with sepsis requiring mechanical ventilation in the intensive care unit

  • Patients requiring fluid assessment or fluid resuscitation based on clinical findings, including one or more of the following:

    • Heart rate greater than 100 beats per minute
    • Systolic blood pressure less than 90 mmHg
    • Mean arterial pressure less than 65 mmHg
    • Urine output less than 0.5 mL/kg/hour for at least 2 hours

Exclusion Criteria:

• Intracranial pathology associated with raised intracranial pressure, including intracerebral hemorrhage or space-occupying lesions
• Recent neurosurgical procedures or conditions where passive leg raising may increase intracranial pressure
• Known heart failure
• Significant cardiac arrhythmias
• Significant valvular heart disease
• Status asthmaticus
• Pulmonary hypertension
• Pulmonary embolism
• Pregnancy
• Lower limb conditions preventing passive leg raising, including fractures
• Intra-abdominal hypertension
• Recent abdominal surgery
• Known carotid artery disease or common carotid artery stenosis greater than 50%