The purpose of this study is to find out if non-invasive dynamic parameters can predict fluid responsiveness in spontaneous breathing patients.

Knowing when to give fluids to the patient is very important in fluid therapy.It is appropriate to administer it to patients whose cardiac output will increase when the fluid is administered (a patient with fluid responsiveness). Appropriate fluid administration can hemodynamically stabilize the patient's condition and reduce unnecessary fluid administration, thereby reducing complications that occur when fluid is insufficient or excessive fluid is administered.

The most commonly used dynamic variables in clinical practice are pulse pressure variation (PPV), stroke volume variation (SVV), and systolic pressure variation that can be obtained by invasive arterial tube insertion. However, recently a non-invasive monitoring method is being used in more and more areas, and in many cases it is necessary to closely monitor the patient's hemodynamic status without mounting an arterial catheter. Therefore, if the variables measured by a non-invasive method can predict fluid responsiveness at a reliable level, it will be of great help in clinical practice.

According to previous studies, dynamic variables can relatively accurately predict fluid responsiveness only in patients undergoing mechanical ventilation. However, in actual clinic, it is necessary to evaluate fluid reactivity even in patients who are not under mechanical positive pressure ventilation. Accurate fluid treatment should be performed during or after surgery under spinal anesthesia in the recovery room. In addition, there are cases in which dynamic variables must be monitored non-invasively in spontaneous breathing patients who do not undergo mechanical ventilation even in intensive care units.

It is clinically meaningful to predict fluid responsiveness in spontaneous breathing patients using such a non-invasive method of monitoring. However, there is limited data on how to evaluate fluid responsiveness in these patient groups. Therefore, the purpose of this study is to evaluate whether fluid responsiveness can be predicted in spontaneous breathing patients using non-invasive dynamic variables.

Inclusion Criteria:

• for patients undergoing surgery under actual spinal anesthesia whose estimated blood loss during surgery is moderate to high (e.g. total knee arthroplasty, total hip arthroplasty)
• Patients with a history of cerebrovascular disease
• Patients with a history of 1 or 2 vessel disease
• Left ventricle ejection fraction (LVEF) Patients with 30% or more and less than 55% of these patients
• Patients who need close hemodynamic monitoring during operation
• ASA (American Society of Anesthesiology) physical status classification system I, II, III
• no difficulty in passive leg raising maneuver

Exclusion Criteria:

• Patients unable to communicate
• Patients who cannot or have difficulty in PLR (passive leg raising) maneuver (patients who cause pain when performing PLR due to trauma of the lower extremities, patients with spine disease that causes pain during PLR, and patient applying splint due to a fracture of the lower extremity)
• Patients unable to attach the finger cuff of the ClearSight sytem to one of the fingers of both hands. (Patients applying a splint due to a fracture of both upper limbs, etc.)
• Patients unable to perform transthoracic ultrasound examination (multiple trauma patients with rib fracture, etc.)
• Patients having difficulty obtaining blood pressure waveforms through the ClearSight system due to poor peripheral vascular perfusion (uncontrolled diabetes patients, patients with peripheral vascular disease, etc.)
• Patients with arrhythmia with moderate or higher risk such as atrial fibrillation or atrial flutter
• Heart failure patients with less than 30% of the left ventricular ejection fraction(LVEF) on echocardiography or patients with moderate to severe left ventricular wall motor dysfunction, or patients with cardiovascular disease of 3 vessel disease
• Other patients who are not appropriate to participate in the study as judged by the researcher