TAP vs. ESP Blocks for Post-Cesarean Analgesia

Background:

Postoperative pain after cesarean delivery has a dual nature: a somatic component resulting from the abdominal wall incision and a visceral component arising from uterine contraction and tissue trauma (innervated by Th10-L1 segments). According to PROSPECT (2021) guidelines, multimodal analgesia is the standard of care. Interfascial plane blocks, such as the Transversus Abdominis Plane (TAP) block and the Erector Spinae Plane (ESP) block, have shown efficacy in controlling somatic pain. However, data comparing their differential efficacy on visceral versus somatic pain components are limited. The ESP block, performed at the L1 level, theoretically offers superior visceral analgesia due to the spread of local anesthetic to the dorsal rami of spinal nerves and potential craniocaudal spread into the paravertebral/epidural space.

Study Design:

This is a prospective, single-center, randomized, single-blind controlled trial conducted at the Maternity Hospital in Taganrog, Rostov Oblast, Russia. A total of 162 patients undergoing elective cesarean delivery under spinal anesthesia will be enrolled. Participants will be randomly assigned in a 1:1:1 ratio to one of three parallel groups:

1. ESP Block Group: Patients will receive a bilateral ultrasound-guided ESP block at the L1 level in the post-anesthesia care unit. 20 mL of 0.375% ropivacaine will be injected on each side (total 40 mL).
2. TAP Block Group: Patients will receive a bilateral ultrasound-guided TAP block in the post-anesthesia care unit. 20 mL of 0.375% ropivacaine will be injected on each side (total 40 mL).
3. Control Group: Patients will receive standard postoperative analgesia without interfascial blocks. This includes ketoprofen 100 mg IM at 4 hours, and oral paracetamol + ketoprofen at 12 hours. Rescue analgesia (trimeperidine 20 mg IM) will be provided if the pain score exceeds 4 on the Numerical Rating Scale (NRS).

All patients will undergo spinal anesthesia with hyperbaric bupivacaine 0.5% (2.2 mL) at the L2-L3 interspace. Preoperatively, pain threshold will be assessed using Nevidimova's method.

Outcome Measures:

The primary outcome is the intensity of visceral pain measured by the Numerical Rating Scale (NRS, 0-10) at 2, 4, 8, 12, and 16 hours postoperatively. Visceral pain is defined as dull, cramping lower abdominal pain.

Secondary outcomes include:

• Intensity of somatic pain (NRS 0-10) at the same time points.
• Time to independent mobilization (hours).
• Time to first mother-infant skin-to-skin contact (hours).
• Consumption of rescue analgesia (number of trimeperidine injections).
• Incidence of adverse events (hypotension, nausea, vomiting, pruritus, signs of local anesthetic systemic toxicity).

Statistical Analysis:

Based on a power analysis (80% power, α=0.05), a minimum of 54 patients per group (162 total) is required to detect a clinically significant difference of 1.5 points in visceral pain scores. Data will be analyzed using the Kruskal-Wallis test for between-group comparisons and the Friedman test for within-group dynamics. A p-value < 0.05 will be considered statistically significant.

Ethical Considerations:

The study is conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. All participants will provide written informed consent. Personal data will be coded and stored securely. The study has been approved by the Local Ethics Committee of I.M. Sechenov First Moscow State Medical University.