Arterial Stiffness and Hemodynamics in Cardiac Surgery

Background:

Hypotension during anesthesia induction is a serious clinical condition that may lead to adverse perioperative outcomes such as myocardial ischemia, renal hypoperfusion, and neurological complications. In cardiac surgery, hypotension during induction can compromise myocardial perfusion and increase the risk of ischemic events. In patients with significant coronary artery disease, a sudden drop in systemic blood pressure can reduce coronary perfusion pressure, potentially resulting in left ventricular dysfunction and hemodynamic instability. Therefore, careful hemodynamic management and appropriate use of vasopressors during anesthesia induction are critical to improving perioperative outcomes in open cardiac surgery.

Arterial stiffness refers to the reduced elasticity of arterial walls due to loss of elastic tissue. It increases with age and is associated with a higher risk of cardiovascular disease. Arterial stiffness can be assessed using ultrasonography (USG) or applanation tonometry. Ultrasonographic pulse wave velocity (PWV) measurements are comparable to those obtained via tonometry. Arterial stiffness has become nearly synonymous with PWV, but research on stiffness index and ultrasonographic stiffness measurements remains limited. The predictive role of arterial stiffness in anesthesia-induced hypotension has not been adequately evaluated. This study was designed to address this gap by evaluating whether arterial stiffness and stiffness index measured by USG can predict hypotension during anesthesia induction. Exploratory analyses also examined associations with intraoperative hemodynamic changes, vasoactive drug use, ICU and hospital stay, and mortality.

Methods:

This prospective study was conducted between October 1, 2022, and May 1, 2023, at a university hospital. Ethical approval was obtained from the institutional review board. Patients scheduled for elective cardiac surgery were evaluated. Arterial stiffness and stiffness index values measured by ultrasonography, along with intraoperative and postoperative clinical data, were analyzed. Informed consent was obtained from all participants.

Participants:

Patients aged 18-85 years scheduled for elective cardiac surgery were included. Exclusion criteria included arrhythmia, end-stage renal disease, left ventricular ejection fraction <35%, reoperation, emergency surgery, body mass index >40 kg/m², and incomplete data. Upon arrival in the operating room, standard monitoring was initiated, including ECG, SpO₂, and invasive arterial pressure via radial artery cannulation under local anesthesia. All arterial stiffness measurements were performed by a single clinician after sedation with midazolam and fentanyl. Measurements were conducted in the supine position, followed by anesthesia induction and central venous catheterization. Hemodynamic parameters, hypotension episodes, and vasoactive agent use were recorded throughout the surgical procedure. After surgery, participants were transferred to the intensive care unit.

Measurements - Pulse Wave Velocity (PWV):

A 3-lead ECG was connected to the patient. Measurements were taken in the supine position with the head turned to the left. A sector probe was placed at the bifurcation of the right sternocleidomastoid muscle to visualize Doppler waveforms of the carotid artery. A linear probe was used to measure maximum and minimum diameters of the carotid artery. The femoral artery was imaged below the inguinal ligament. Doppler signals were recorded from both sites simultaneously with ECG. The time delay between the ECG R-wave and the start of the Doppler waveform was measured across three cardiac cycles and averaged. The distance between the measurement points was divided by the delay time to calculate PWV (m/s). This value represented arterial stiffness.

The stiffness index (β) was calculated using the maximum and minimum diameters of the carotid artery and systolic/diastolic blood pressure values:

β = [ln(Systolic BP / Diastolic BP)] / [(Systolic Diameter - Diastolic Diameter) / Diastolic Diameter] The vasoactive inotropic score (VIS) was used to assess the degree of vasopressor and inotropic support. A VIS ≥10 is considered an independent risk factor for increased morbidity and mortality.

Data Collection:

Baseline systolic, diastolic, and mean arterial pressures and heart rate values were recorded pre-induction, pre-intubation, and within the first 10 minutes post-intubation. Additional hemodynamic parameters such as systolic pressure variation (SPV), pulse pressure variation (PPV), and central venous pressure (CVP) were also collected. Intraoperative hypotension was defined as systolic arterial pressure (SAP) <90 mmHg. Thresholds of <80 mmHg and <70 mmHg were also explored. The types and doses of vasoactive and inotropic agents used during surgery, including during cardiopulmonary bypass, were recorded. VIS values were calculated and analyzed in relation to arterial stiffness parameters.