The aim of this study is to investigate the reliability of corrected carotid flow time (ccFT) and the percentage change in peak flow velocity (ΔVpeak), as non-invasive methods for assessing fluid responsiveness using the passive leg raising (PLR) test in patients undergoing coronary bypass surgery.

This study is a single-center, prospective, and observational research. After obtaining approval from the ethics committee, 50 patients scheduled for elective coronary artery bypass surgery under general anesthesia at the Cardiovascular Surgery operating room of the Ministry of Health Ankara City Hospital will be included in the study. The study is designed as a single-center, prospective, and observational trial.

Patient data including weight, height, age, gender, BMI (body mass index), ASA classification, left ventricular ejection fraction, comorbidities, and medications will be recorded. Anesthesia induction and management will be performed in accordance with the routine practice of the anesthesia clinic. After the patient is brought to the operating table, in addition to standard hemodynamic monitoring with non-invasive blood pressure (NIBP), 5-lead ECG, and pulse oximetry, bispectral index (BIS), body temperature, and cardiac output monitoring with the Pulsion Flex device will be performed. Parameters measured by the Pulsion Flex device (CI, SVI, SVRI, SVV, PPV, DO2I, dPmx) will be recorded before and after anesthesia induction. General anesthesia will be induced with preoxygenation followed by 0.05 mg/kg midazolam, 1 mg/kg lidocaine, 3 mcg/kg fentanyl, and 2 mg/kg propofol. Muscle relaxation will be achieved with 0.6-0.8 mg/kg rocuronium, and orotracheal intubation will be performed with an appropriate tube. The target BIS value will be maintained within 40-60, and anesthesia will be maintained by adjusting the concentration of volatile anesthetics and remifentanil infusion dose (0.05-0.2 mcg/kg/min) according to hemodynamic parameters.

Ventilation mode and parameters will be set as follows: tidal volume 8 ml/kg based on ideal body weight, respiratory rate adjusted to maintain end-tidal CO₂ between 30-40 mmHg, inspiration/expiration ratio 1:2, positive end-expiratory pressure (PEEP) 5 cmH₂O, and FiO₂ 50%. After Allen's test is performed, radial artery catheterization of the non-dominant hand will be performed for invasive blood pressure monitoring, and a 7 Fr triple-lumen central venous catheter will be inserted into the right internal jugular vein for central venous pressure (CVP) monitoring. These procedures are routinely performed in patients scheduled for open thoracic surgery in our clinic. Preferably, two large-bore peripheral intravenous lines will also be inserted. Measurements will begin once patient preparation is complete, during a hemodynamically stable period, and when spontaneous respiratory effort is absent.

After the patient is placed in a 45-degree head-up semi-sitting position, hemodynamic parameters will be recorded: heart rate (HR, beats/min), systolic arterial pressure (SAP, mmHg), diastolic arterial pressure (DAP, mmHg), mean arterial pressure (MAP, mmHg), stroke volume index (SVI), cardiac index (CI), PPV, and SVV. Corrected carotid flow time (ccFT) and the percentage change in peak velocity (ΔVpeak), measured using Doppler ultrasound, will also be recorded. Ultrasound measurements will be performed with a 4-12 MHz linear probe in vascular mode. With the patient's head tilted 30 degrees to the left, a longitudinal view of the right common carotid artery will be obtained below the lower border of the thyroid cartilage, and measurements will be taken 2 cm proximal to the carotid bifurcation. Doppler will be activated, and the sample volume will be placed at an angle less than 60 degrees in the region with optimal color flow. Flow time will be measured from the beginning of the systolic upstroke to the dicrotic notch.

After one minute of passive leg raising (PLR), hemodynamic parameters as well as ccFT and ΔVpeak will be measured again and recorded. Patients demonstrating a ≥10% increase in CI measured by the Pulsion Flex device after PLR will be classified as fluid responsive, while those without such an increase will be classified as non-responders. The differences in ccFT and ΔVpeak parameters between the two groups will be analyzed.

Inclusion Criteria:

A total of 50 patients undergoing elective coronary artery bypass surgery under general anesthesia in the Cardiovascular Surgery operating room of the Ministry of Health Ankara Bilkent City Hospital will be included in the study.

The volunteers to be included will be patients aged between 18 and 80 years, evaluated as ASA class II-III according to the American Society of Anesthesiologists (ASA) classification.

Exclusion Criteria:

Patients who do not wish to participate in the study

Patients younger than 18 or older than 80 years

Patients with an ASA score greater than III

Patients with BMI > 35

Patients with EF < 40%

Patients with atrial fibrillation

Patients with severe valvular stenosis or insufficiency

Patients with right ventricular dysfunction

Patients with carotid artery stenosis

Patients with a history of cerebrovascular accident or transient ischemic attack

Patients with increased intra-abdominal or intracranial pressure

Patients with glaucoma

Patients with severe renal or hepatic disease

Patients who develop hemodynamic instability during the perioperative period

Pregnancy

A total of 50 patients undergoing elective coronary artery bypass surgery under general anesthesia in the Cardiovascular Surgery operating room