Comparison of the Effectiveness of Midpoint Transverse Process to Pleura (MTP) Block and Erector Spinae Plane (ESP) Block in Video-Assisted Thoracoscopic Surgery (VATS) at RS Ngoerah

Background and rationale Postoperative pain of moderate to severe intensity is still common in the first 24 hours after video-assisted thoracoscopic surgery (VATS) despite its minimally invasive nature. Inadequately treated pain can lead to splinting, atelectasis and chronic post-surgical pain. At RS Ngoerah, postoperative analgesia after VATS is not yet standardized and relies on intravenous systemic opioids or thoracic epidural anesthesia. Ultrasound-guided fascial plane blocks are recommended as components of enhanced recovery protocols.

The erector spinae plane (ESP) block places local anesthetic in the fascial plane between the erector spinae muscle and the transverse process. Analgesia depends mainly on blockade of the dorsal rami, and spread to the thoracic paravertebral space is variable. The midpoint transverse process to pleura (MTP) block places the needle tip midway between the posterior edge of the transverse process and the pleura. It is closer to the thoracic paravertebral space but still posterior to the superior costotransverse ligament, and is expected to give more reliable spread to the paravertebral space, with a theoretically higher risk of pneumothorax than the ESP block. To the investigators' knowledge, no randomized trial has directly compared the two blocks exclusively in VATS, and the Quality of Recovery-15 (QoR-15) has not been compared between them in thoracic surgery.

Study design Randomized, double-blind, parallel-group controlled trial at a single center (Central Surgical Installation, RS Ngoerah, Denpasar, Indonesia) in adult patients undergoing elective VATS. Outcomes are measured only after the intervention, without a baseline measurement, because baseline conditions of the two groups are assumed to be equal through randomization. Participants receive the block after induction of general anesthesia and are therefore unaware of the block type. Outcomes are assessed by the Acute Pain Service (APS) team, who are blinded to group allocation. The blocks are performed by a consultant anesthesiologist (regional analgesia consultant) of the Department of Anesthesiology and Intensive Therapy, RS Ngoerah, who follows the randomization envelope and does not assess outcomes.

Participants and sampling Consecutive sampling of eligible adult patients (age 18-65 years, ASA I-III, BMI 18-30 kg/m2) scheduled for elective VATS. Planned total sample size is 48 participants (24 per group).

Randomization and allocation concealment Block randomization, with the list generated using randomizer.org. The list is kept in sealed, opaque, sequentially numbered envelopes that are opened only by the block operator shortly before the patient enters the operating room, after eligibility is confirmed. The allocated block is recorded by the operator and is not communicated to the assessor or the patient.

Perioperative protocol Preoperative: eligibility screening by the investigator, written informed consent, education on PCA use, and recording of baseline data (age, sex, BMI, ASA status, diagnosis, planned VATS procedure, INR, platelet count, preoperative opioid use) from the medical record and direct measurement.

Intraoperative: standard ASA monitoring. Induction with propofol 1.5-2.0 mg/kg, fentanyl 2 mcg/kg and rocuronium 0.6 mg/kg intravenously, with double-lumen tube intubation as required by the VATS procedure. Maintenance with sevoflurane 0.8-1 MAC and fentanyl 0.5-1 mcg/kg every 30-45 minutes, titrated to hemodynamic response. The block is performed under general anesthesia in the lateral decubitus position, at least 15 minutes before surgical incision (see intervention descriptions). VATS is performed by the thoracic surgery team of RS Ngoerah using standard technique. Ibuprofen 400 mg IV and paracetamol 1 g IV are given 30 minutes before wound closure in all participants.

Postoperative (0-24 hours): fentanyl PCA is started immediately after arrival at the PACU (10 mcg/mL, demand only, demand dose 20 mcg, lockout interval 10 minutes, maximum 200 mcg per 4 hours, no background infusion), programmed identically in both groups. If NRS is 4 or higher at a scheduled assessment, rescue analgesia is a 20 mcg fentanyl bolus delivered through the PCA pump and pressed by the patient. The time of the first rescue is recorded to the minute from nursing records or the PCA log.

Outcome assessment All assessments are made by the blinded APS team. Total PCA fentanyl is read from the cumulative PCA pump log at 24 hours and expressed in mcg/kg. NRS (0-10) at rest and on movement is obtained by guided interview at 0, 1, 2, 4, 6, 12 and 24 hours after the end of surgery. Time to first rescue analgesia is taken from nursing records and the PCA log. The Indonesian version of the QoR-15 is completed by the participant at 24 +/- 2 hours after surgery.

Sample size Sample size per group was calculated with the formula for unpaired numeric comparison (alpha 5%, power 90%) for four outcomes: total PCA fentanyl at 24 hours (16 per group), NRS at 12 hours (16 per group), time to first rescue analgesia (21 per group) and QoR-15 at 24 hours (17 per group). The largest requirement (21 per group) was adopted and, with a 10% drop-out allowance, 24 per group (48 in total) is planned.

Statistical analysis Analysis is per-protocol: only participants who complete the protocol are analyzed. Numeric variables are summarized as mean and standard deviation or median and interquartile range, according to the distribution; categorical variables as frequency and percentage. Normality is tested with the Shapiro-Wilk test and homogeneity of variance with Levene's test. NRS scores at the seven time points are analyzed as repeated measures (repeated-measures ANOVA with group and time factors and the group x time interaction when data are normally distributed; non-parametric Friedman test otherwise). Total PCA fentanyl, time to first rescue analgesia and QoR-15 are compared between groups with the independent t-test, or the Mann-Whitney U test when assumptions are not met. Potential covariates (type of VATS procedure, duration of surgery, duration of anesthesia, intraoperative fentanyl) are included in the comparative analysis if baseline comparability testing shows a significant difference between groups. A p value below 0.05 is considered statistically significant. Software: IBM SPSS Statistics version 25.0 or R version 4.0 or higher.

Withdrawal and drop-out criteria Conversion from VATS to open thoracotomy; technical failure of the regional block confirmed by the operator, so the participant does not receive the intervention as specified; death within the 24-hour follow-up; postoperative mechanical ventilation; complications during care such as local anesthetic systemic toxicity (LAST) or allergic reaction/anaphylaxis; withdrawal from the study at any time during data collection.

Safety monitoring Signs and symptoms of LAST (agitation, seizure, arrhythmia), pneumothorax, and opioid adverse events (respiratory depression, postoperative nausea and vomiting, pruritus) are recorded systematically on the case report form. Serious adverse events are reported to the research ethics committee.

Ethics The protocol was approved by the Research Ethics Committee, Faculty of Medicine, Universitas Udayana (protocol number 2026.02.1.0705, approval date 3 June 2026). Written informed consent is obtained from all participants.