This study aims to evaluate the correlation between stroke volume measurements obtained by transthoracic echocardiography and bioreactance-based noninvasive cardiac output monitoring. The primary objective is to assess the level of agreement between these two modalities in critically ill patients.

In this prospective observational study, patients presenting with clinical signs of shock will be enrolled after obtaining informed consent. Stroke volume (SV) will be measured using both transthoracic echocardiography and bioreactance-based noninvasive cardiac output monitoring (Cheetah NICOM). SV will be recorded before and after passive leg raising (PLR) to evaluate the correlation between the two methods in terms of absolute values and directional changes (increase or decrease). No therapeutic intervention will be performed as part of the study; all clinical decisions will remain under the discretion of the treating medical team.

Inclusion Criteria

• Age ≥ 18 years
• Clinical diagnosis of shock as determined by the treating ICU physician (e.g., hypotension requiring vasopressors or evidence of end-organ hypoperfusion)
• Able to obtain informed consent from the patient or a legally authorized representative
• Enrollment within 24 hours of ICU admission

Exclusion Criteria:

• Pregnancy
• Known severe aortic valve disease or dynamic left ventricular outflow tract obstruction
• Morbid obesity (BMI > 40) that precludes accurate echocardiographic imaging Presence of cardiac arrhythmias (e.g., atrial fibrillation with rapid ventricular response) affecting stroke volume measurements
• Implanted cardiac assist devices (e.g., LVAD, pacemaker dependency)
• Imminent death or decision for comfort care only

Adult patients admitted to the intensive care unit (ICU) with clinical signs of shock, including hypotension and/or evidence of end-organ hypoperfusion, who are able to provide informed consent or have a legally authorized representative available.

Individual participant data (IPD) will not be shared due to privacy concerns and the limited scope of this single-center observational study. No long-term data storage or external data-sharing infrastructure has been established for this project.