Effects of Esketamine and Bilateral Lower Limb Elevation on Hemodynamic Stability During Induction of General Anesthesia in Elderly Patients Undergoing Thoracic Surgery

Video-assisted thoracoscopic surgery (VATS) is now widely used in thoracic surgery due to its small incisions, low stress response, and high patient tolerance Compared to open thoracotomy, VATS is associated with fewer complications, shorter hospital stays, and better postoperative quality of life . Although VATS is a minimally invasive procedure, damage to the pleura and lung parenchyma, traction on the intercostal nerves, and stimulation from chest tubes can still cause severe postoperative pain. This pain affects patient mobility, such as turning over and getting out of bed, potentially leading to complications like atelectasis and pulmonary infections. Approximately 78% of patients experience moderate to severe pain after surgery, and 50% do not receive adequate analgesia \[3\]. Effective postoperative pain management is crucial for patient recovery and reducing pulmonary infections. To further ensure postoperative comfort and accelerate recovery, the combined use of general anesthesia with regional nerve blocks has been recommended in recent years. Regional blocks can not only effectively alleviate postoperative pain but also help reduce the dosage of general anesthetics, promoting faster patient recovery. Thoracic paravertebral block (TPVB), as an effective regional anesthesia technique, is often used to manage postoperative pain after VATS . TPVB involves injecting local anesthetics near the thoracic spinal nerves as they exit the intervertebral foramen, blocking the ipsilateral somatic and sympathetic nerves. It is primarily used for analgesia following rib fractures, breast surgery, and open or video-assisted thoracic surgery. However, performing TPVB before surgery blocks both the thoracic nerves and the exposed sympathetic nerves. When sympathetic nerves are inhibited, myocardial contractility and heart rate decrease, while peripheral vascular resistance drops. Furthermore, the rapid administration of multiple drugs during general anesthesia induction can increase the incidence of hypotension during this period . Esketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist with stronger sedative and analgesic effects and fewer adverse events compared to ketamine. Some studies have shown that sub-anesthetic doses of esketamine (typically 0.15-0.3 mg/kg) can reduce the incidence of adverse events, such as induction hypotension and opioid-induced cough, through its sympathetic stimulatory, analgesic, and NMDA receptor antagonistic effects. In cases of acute circulatory failure, the passive leg raising (PLR) test is used to assess whether cardiac output increases with volume expansion. By shifting approximately 300 mL of venous blood from the lower limbs to the right heart, PLR serves as a test of fluid responsiveness. Its hemodynamic effects can be quickly reversed by changing position, thus avoiding the risk of fluid overload. Based on this principle, elevating the patient's lower limbs during anesthesia induction can rapidly and transiently increase venous return to the heart, thereby reducing the occurrence of induction hypotension. Elevating both lower limbs enhances venous return from the legs, increasing preload to the heart, improving cardiac output, and helping to maintain stable blood pressure to some extent. The induction period of general anesthesia is a phase of frequent hemodynamic changes. Elderly patients, often with multiple comorbidities and reduced physiological reserve, are more susceptible to hemodynamic disturbances caused by induction drugs. Studies indicate that approximately 40% of elderly patients experience hemodynamic alterations during induction . Sustained or severe hypotension may lead to inadequate organ perfusion and ischemia, potentially increasing the risk of postoperative complications such as myocardial injury, ischemic stroke, and acute kidney injury . Therefore, preventing hypotension after induction in elderly patients holds significant clinical value for reducing postoperative complications. The administration of opioids, propofol, and muscle relaxants during general anesthesia induction can cause hypotension due to arterial dilation and reduced peripheral vascular resistance. Since TPVB blocks sympathetic nerves, it may make patients more prone to hypotension during induction. This study hypothesizes that using esketamine or elevating the lower limbs during induction can reduce the incidence of hypotension in elderly patients.