A Study Comparing Carotid Doppler Ultrasound and Echocardiography to Assess Fluid Responsiveness in Septic Patients on Ventilator

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.