The aim of this study is to evaluate the effect of the erector spinae plane block, used to reduce postoperative pain, on cerebral oxygenation in thoracic surgery patients undergoing one-lung ventilation in the lateral decubitus position.

Pulmonary resection is one of the most frequently performed procedures in thoracic surgery. Lung resections are primarily carried out for the diagnosis and treatment of pulmonary malignancies and, less commonly, for the management of pulmonary bullae, bronchiectasis, complicated infectious lung diseases, and traumatic lung injuries.

During surgery, patients are placed in the lateral decubitus position, and one-lung ventilation (OLV) is employed during both open and endoscopic thoracic procedures to restrict lung movement and to improve surgical exposure and operative conditions.

Thoracotomy is considered one of the most painful surgical procedures in thoracic surgery. It is well established that inadequately controlled intraoperative and postoperative pain adversely affects functional recovery. Despite the use of potent analgesics, patients may experience severe postoperative pain. Consequently, significant hemodynamic instability may occur even under general anesthesia during thoracotomy. In addition, pain may impair respiratory mechanics, leading to atelectasis and other postoperative pulmonary complications.

In the erector spinae plane block (ESPB), anatomical landmarks are identified under ultrasound guidance, and a local anesthetic is administered beneath the erector spinae muscle at the level just above the transverse process of the vertebra, providing thoracic anesthesia. ESPB is frequently used to provide postoperative analgesia in patients undergoing pulmonary surgery in thoracic practice.

It is well recognized that ESPB offers several advantages over traditional techniques performed close to the neuraxis. First, the target structure is easily visualized with ultrasound, and needle advancement toward the target is relatively simple, making the technique easy to perform. In addition, the complication rate associated with this block is relatively low. Critical structures that may result in serious complications if injured-such as the pleura, vascular structures, and the spinal cord-are located away from the needle trajectory. Considering its technical simplicity and relative safety, several authors have suggested that ESPB may be incorporated as a component of multimodal analgesia during the perioperative period.

In anesthesiology and critical care practice, pulse oximetry is the most commonly used standard method for assessing oxygenation. In pulse oximetry, a probe is typically placed on the distal extremities to measure oxygen-saturated hemoglobin levels. However, in conditions predisposed to hypoxemia-such as one-lung ventilation, cardiac surgery, or hypotensive anesthesia-pulse oximetry may be insufficient for accurately reflecting cerebral oxygenation. Therefore, cerebral oximeters have been specifically designed to assess cerebral oxygenation. Near-infrared spectroscopy (NIRS) reliably reflects changes in cerebral oxygenation. rSO₂ index values obtained during periods of hypercapnia, hypocapnia, hypoxemia, and arterial hypotension provide valuable information regarding cerebral oxygenation status.

NIRS is a noninvasive optical technique used to assess tissue oxygenation and was first introduced by Jobsis in 1977 . Similar to pulse oximetry, NIRS utilizes light wavelengths between 700 and 1000 nm and measures the difference between oxyhemoglobin and deoxyhemoglobin through transcutaneous probes, thereby reflecting oxygen uptake in the underlying tissue. This measurement is interpreted as regional oxygen saturation (rSO₂).

Since venous blood volume in the frontal region of the brain accounts for approximately 70-75% of total cerebral blood volume, monitoring this region is considered meaningful for the assessment of cerebral oxygenation. Studies investigating NIRS have demonstrated a significant reduction in oxygenation of the prefrontal cortex-an area critical for higher-order and central cognitive functions-during hypoxic exposure.

A cerebral rSO₂ value below 50% or a reduction greater than 20% from baseline has been associated with postoperative cognitive dysfunction and prolonged hospital stays. Furthermore, cerebral oxygen desaturation episodes have been shown to be associated with postoperative neurocognitive dysfunction, and monitoring and treating these episodes may reduce the incidence of postoperative neurocognitive impairment.

Using the NIRS technique, regional cerebral tissue oxygen saturation can be assessed continuously during the intraoperative period. When rSO₂ values fall below critical thresholds, clinicians are alerted, allowing corrective interventions to be implemented to ensure adequate cerebral oxygenation.

During thoracic surgery, the use of OLV and the lateral decubitus position leads to multiple changes in oxygenation, ventilation, and overall physiology. Even when effective hypoxic pulmonary vasoconstriction occurs to improve oxygenation during OLV, intrapulmonary shunting still develops, resulting in alterations in systemic oxygenation and hypoxia. Therefore, close monitoring of oxygenation and ventilation during OLV is of vital importance in thoracic anesthesia.

The primary aim of this study is to evaluate the effect of preoperatively administered ESPB on intraoperative NIRS values. The secondary aim is to compare hemodynamic parameters and intraoperative remifentanil requirements between patients

Inclusion Criteria:

• Patients aged 18-80 years
• With an American Society of Anesthesiologists (ASA) physical status of I-III
• Glasgow Coma Scale (GCS) score of 13-15
• Scheduled for thoracic surgery requiring one-lung ventilation

Exclusion Criteria:

• Patients undergoing emergency surgery
• Those younger than 18 years or older than 84 years
• Patients with an American Society of Anesthesiologists (ASA) physical status of IV or V
• Patients who refused to participate in the study
• Those with a history of brain surgery for any reason
• Patients with defects in the frontal region preventing placement of near-infrared spectroscopy probes
• Patients with distorted thoracic vertebral anatomy for any reason resulting in inadequate ultrasonographic imaging for block performance
• Patients with a known allergy to local anesthetics
• Patients with neurological disorders such as Alzheimer's disease or dementia
• Patients who were illiterate and/or unable to establish effective communication

Individual participant data were not shared due to ethical and privacy considerations