Analgesic management in thoracic surgery is a challenge for the anesthesiologist, as thoracotomy is one of the surgical procedures with the most intense postoperative pain, which can impact respiratory function and the patient's subsequent recovery. Epidural analgesia is the gold standard. When epidural catheter placement is not possible, erector spinae plane block is a safe alternative, as the ultrasound target is easily visualized and the injection site is far from the neuraxis, pleura, and major vascular structures. Therefore, this block has been increasingly established in routine clinical practice as an option for patients with additional difficulties or as an alternative technique for those for whom epidural catheter placement is not possible. The main objective of this study is to evaluate postoperative analgesia in patients undergoing elective thoracic surgery.

Design and study population A prospective, observational follow-up study will be conducted. ASA I-III patients undergoing scheduled thoracic surgery between November 1 and December 31, 2025, will be included. Their analgesic management will be based on standard clinical practice.

The gold standard for analgesic management after thoracic surgery is the administration of local anesthetic, with or without opioids, through a catheter placed in the epidural space during the 48 hours following surgery. However, there are situations in which the placement of this catheter is contraindicated (due to patient refusal, coagulation disorders, spinal pathology, etc.) or in which the risk-benefit assessment makes it necessary to consider alternatives (it may lead to hypotension or bradycardia that compromises patients with cardiovascular disease, urinary retention, nerve injury, or spinal hematoma). This has led anesthesiologists to seek alternatives, among which paravertebral block has been investigated, with excellent results, although it is not exempt from the risks associated with a central block and has contraindications similar to those of epidural analgesia. When epidural catheter placement is not possible, erector spinae plane block is a safe alternative, as the ultrasound target is easily visualized and the injection site is far from the neuraxis, pleura, and major vascular structures. Therefore, this block has been increasingly established in routine clinical practice as an option for patients with additional difficulties or as an alternative technique for those for whom epidural catheter placement is not possible. The main objective of this study is to evaluate postoperative analgesia in patients undergoing elective thoracic surgery.

Design and study population A prospective, observational cohort study will be conducted. Patients will be followed from the day of hospital admission (usually 24 hours before surgery, when informed consent will be requested) until hospital discharge.

Perioperative analgesic management will be carried out according to standard clinical practice, after evaluation by the anesthesiologist in charge of intraoperative anesthesia management.

ASA I-III patients scheduled for thoracic surgery at the Doctor Negrín University Hospital of Gran Canaria between November 1 and December 31, 2025, will be included in the study. An estimated 80 patients will be included in this prospective, observational study.

On the day of the procedure, analgesic management will be administered according to the standard clinical practice of the anesthesiologist responsible for the patient's clinical management. The anesthesiologist will be unaware that the patient's perioperative analgesic management will be evaluated by this study. In all patients for whom a regional procedure (epidural catheter or erector spinae plane block) is performed, standard aseptic measures will be followed during the procedure.

The epidural catheter will be placed according to standard clinical practice using the loss-of-resistance technique in the space between the dorsal spinous processes corresponding to the surgical wound site, prior to the patient's anesthesia induction. The anesthesiologist responsible for the patient's perioperative management will decide whether or not to use this catheter to administer analgesics during the intraoperative period or whether to administer intraoperative analgesics with or without the administration of intravenous opioids in combination with non-opioid analgesics.

For patients undergoing an erector spinae plane block, the procedure will be performed using ultrasound with a high-frequency linear ultrasound probe, locating the puncture point 3 cm lateral to the spinous process. The puncture is made at the level of T5, in the craniocaudal plane, using a 50 mm EchoPlex needle, until the needle bevel is seen at the level of the transverse process, immediately anterior to the erector spinae muscle group. At this point, 3 ml of the local anesthetic selected by the anesthesiologist in charge of perioperative management of the patient is injected, visualizing the dissection of the interfascial plane. If adequate dissection of this plane is confirmed during the injection of these 3 ml, the remaining local anesthetic will be injected until the target volume is reached, without exceeding the toxic dose for each patient. 7 Intraoperative anesthetic management will be carried out according to standard clinical practice. At the end of the procedure, after extubation, the patient will be transferred to the Post-Anesthesia Care Unit. Pain will be assessed using a numerical pain scale at 1, 3, 6, 24, and 48 hours postoperatively. Postoperative management will be carried out according to standard clinical practice. The patient's postoperative progress will also be assessed until hospital discharge.

Inclusion Criteria:

• Patients undergoing thoracic surgery between July 1 and October 31, 2020.
• Age over 18.
• ASA I-III.
• Signed informed consent

Exclusion Criteria:

• ASA IV-V.
• Chronic opioid treatment or treatment in the Chronic Pain Unit.
• Intravenous drug abuse.
• Local anesthetic allergy.
• Language barrier, cognitive impairment, or inability to participate in clinical assessment during the study.
• BMI <18 or >35 kg/m2

The study will include ASA I-III patients scheduled for thoracic surgery at the Doctor Negrín University Hospital of Gran Canaria between November 1 and December 31, 2025.