The goal of this clinical trial is to compare two different epidural analgesia delivery methods for pain control after total knee arthroplasty in adults undergoing elective surgery. The study will evaluate whether programmed intermittent epidural bolus (PIEB) provides better postoperative analgesia and recovery outcomes than continuous epidural infusion (CEI).

The main questions it aims to answer are:

Does PIEB reduce total epidural local anesthetic consumption during the first 24 postoperative hours compared with CEI? Does PIEB improve postoperative pain control and quality of recovery? Are there differences between the two methods regarding motor block, rescue analgesic requirement, patient-controlled epidural analgesia use, and adverse effects?

Researchers will compare PIEB plus patient-controlled epidural analgesia (PCEA) with CEI plus PCEA in patients undergoing total knee arthroplasty.

Participants will:

Receive combined spinal-epidural anesthesia during surgery Receive postoperative epidural analgesia using either PIEB or CEI Be evaluated for pain scores, motor block, recovery quality, epidural local anesthetic consumption, rescue analgesic requirement, and adverse events during the first 24 postoperative hours

Total knee arthroplasty (TKA) is one of the most commonly performed orthopedic procedures and is associated with significant postoperative pain. Inadequate pain control after TKA may delay mobilization, prolong hospitalization, impair rehabilitation, and negatively affect patient satisfaction and recovery quality. Therefore, optimizing postoperative analgesia while minimizing opioid consumption and preserving motor function is an important component of enhanced recovery after surgery (ERAS) protocols.

Epidural analgesia has been widely used for postoperative pain management for decades. Conventional continuous epidural infusion (CEI) provides stable delivery of local anesthetic but may be associated with uneven epidural spread, higher local anesthetic consumption, and increased motor blockade in some patients.

Programmed intermittent epidural bolus (PIEB) is an alternative epidural drug delivery technique in which local anesthetic is administered automatically at predefined intervals as intermittent boluses rather than as a continuous infusion. Due to the higher injection pressure and intermittent delivery pattern, PIEB may improve epidural spread and analgesic quality while reducing total local anesthetic requirements and motor block. Although PIEB has been extensively investigated in obstetric analgesia, evidence regarding its use in major orthopedic surgery remains limited.

This prospective, randomized, double-blind, parallel-group clinical trial aims to compare PIEB plus patient-controlled epidural analgesia (PCEA) with CEI plus PCEA in patients undergoing elective primary total knee arthroplasty under combined spinal-epidural anesthesia.

A total of 90 participants will be enrolled and randomized in a 1:1 ratio into two groups:

• PIEB + PCEA group
• CEI + PCEA group

Randomization will be performed using a computer-generated randomization sequence with allocation concealment through sequentially numbered opaque sealed envelopes.

All participants will receive standardized combined spinal-epidural anesthesia. Epidural catheter placement will be performed at the L2-L3 interspace using the needle-through-needle technique. Spinal anesthesia will be achieved with 12.5 mg hyperbaric bupivacaine administered intrathecally.

Postoperatively, all participants will receive epidural analgesia using the same epidural solution consisting of 0.1% bupivacaine diluted in normal saline.

In the PIEB group, epidural analgesia will be delivered as programmed intermittent epidural boluses of 6 mL every 60 minutes combined with patient-controlled epidural boluses of 6 mL with a 30-minute lockout interval.

In the CEI group, epidural analgesia will be delivered as continuous epidural infusion at 6 mL/hour combined with patient-controlled epidural boluses of 6 mL with a 30-minute lockout interval.

All participants will additionally receive standardized multimodal analgesia with scheduled paracetamol administration. Intravenous tramadol will be used as rescue analgesia when the visual analog scale (VAS) pain score is 4 or greater.

The primary outcome measure is total epidural local anesthetic consumption during the first 24 postoperative hours.

Secondary outcome measures include:

• Quality of recovery assessed using the QoR-15 questionnaire
• Motor block assessed with the modified Bromage scale
• Number of patient-controlled epidural bolus demands and delivered boluses
• Rescue analgesic consumption
• Resting and movement-related VAS pain scores

Pain scores will be assessed at postoperative 2, 4, 8, 12, and 24 hours. QoR-15 will be evaluated preoperatively and at postoperative 24 hours.

The study will be conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. Written informed consent will be obtained from all participants before enrollment.

Inclusion Criteria:

• Adults aged 18 to 80 years
• American Society of Anesthesiologists (ASA) physical status I-III
• Scheduled for elective primary total knee arthroplasty
• Eligible for combined spinal-epidural anesthesia and postoperative epidural analgesia
• Able to understand and use patient-controlled epidural analgesia
• Provided written informed consent

Exclusion Criteria:

• Refusal to participate in the study
• Known allergy or hypersensitivity to study medications
• Body mass index (BMI) ≥ 40 kg/m²
• Body weight < 40 kg
• Severe cardiac disease, including symptomatic arrhythmia or advanced conduction abnormalities
• Coagulopathy (INR > 1.5 or platelet count < 100,000/mm³)
• Pregnancy or breastfeeding
• Revision total knee arthroplasty or emergency surgery
• Active infection at the site of regional anesthesia
• Chronic opioid use or opioid dependence
• Neurological disease or preexisting motor/sensory deficit in the lower extremities
• ASA physical status IV or V
• Requirement for intraoperative epidural local anesthetic supplementation due to inadequate spinal anesthesia

Individual participant data (IPD) sharing has not yet been determined. De-identified data may be shared upon reasonable request following publication of the study results, subject to institutional and ethical considerations.

Participants, clinical care providers, and postoperative outcome assessors will be blinded to group allocation. Epidural analgesia pumps will be covered to conceal the infusion mode. Epidural solution preparation and pump programming will be performed by a separate unblinded investigator who will not participate in postoperative assessments, patient care, or data collection.