Prospective, Randomized Comparative Study Between an Anesthesiological, Ultrasound-guided, and a Laparoscopic, Landmark-based Application of a "Transversus Abdominis Plane (TAP) Block" Based on Postoperative Pain Perception, Postoperative Analgesic Requirement, and Procedure Duration

The Transversus Abdominis Plane Block (TAP) has become one of the most established and frequently performed trunk wall blocks for perioperative analgesia in abdominal surgical procedures. The TAP-Block can be performed by both surgeons and anaesthetists.

The goal of this prospective, randomized study is to compare an anesthesiological, ultrasound-guided "Transversus Abdominis Plane (TAP) Block" with a laparoscopic, landmark-based "Transversus Abdominis Plane (TAP) Block"

The main questions it aims to answer are:

Primary Hypothesis: There are no differences in postoperative pain perception and analgesic requirements between the anaesthesiological ultrasound-guided and the surgical laparoscopic landmark-based TAP block

Secondary Hypothesis: There are no significant differences in the duration of the procedure between the anaesthesiological, ultrasound-guided and the surgical laparoscopic landmark-based TAP block.

The Transversus Abdominis Plane Block (TAP) has become one of the most established and frequently performed trunk wall blocks for perioperative analgesia in abdominal surgical procedures. A TAP block is a so-called trunk wall block where a targeted injection of high volumes of local anesthetics is made into a space between two muscle fascias, the so-called inter-fascial space. In this inter-fascial space, the cutaneous nerve branches of various anterior rami of the spinal nerves run and innervate somatosensory in the respective dermatome, skin, soft tissues, and bones, as well as the outer layers of the pleura and peritoneum. Specifically, in a TAP block, the nerve fibers of the spinal nerves from the spinal segments Th6 to L1 can be anaesthetized by applying local anaesthetics between the Musculus obliquus internus abdominis and the Musculus transversus abdominis. The block produces somatic analgesia of the skin, muscles, and bony structures. Visceral analgesia of the internal organs is not achieved. Therefore, the TAP block mainly has an indication within the framework of a multimodal pain concept to save central and peripheral analgesics.

In the literature, it is shown that especially laparoscopic procedures benefit from a TAP block in terms of reducing postoperative reported pain intensity and reducing postoperative opioid requirements. Compared to simple wound infiltration with a local anaesthetic or simple local anaesthesia of the trocar insertion sites in a laparoscopy, the TAP block has been shown to be a more effective method in multiple studies.

The so-called Transversus Abdominis Plane compartment can be reached using various approaches (posterior, lateral, subcostal) and puncture techniques (landmark-based, ultrasound-guided, and surgical). A lateral approach is used primarily for analgesia in lower abdominal surgery (e.g., inguinal hernia repair). A subcostal approach is used primarily for analgesia in upper abdominal/supraumbilical surgery (e.g., cholecystectomy). A dual TAP block or '4 quadrant block,' the combination of a lateral with subcostal TAP block, could achieve better abdominal distribution of the local anaesthetic and more complete analgesia for the lower (T10-T12) and upper (T6-T9) abdomen.

The goal of this monocentric, prospective, randomised study is to compare an anesthesiological, ultrasound-guided "Transversus Abdominis Plane (TAP) Block" with a laparoscopic, landmark-based "Transversus Abdominis Plane (TAP) Block" in two parallel study arms.

Anaesthesia Induction and maintenance in both groups are standardised and similar.

The main questions to answer are:

Primary Hypothesis: There are no differences in postoperative pain perception and analgesic requirements between the anaesthesiological ultrasound-guided and the surgical laparoscopic landmark-based TAP block

Secondary Hypothesis: There are no significant differences in the duration of the procedure between the anaesthesiological, ultrasound-guided and the surgical laparoscopic landmark-based TAP block.

A sample size calculation was performed before study start. The hypotheses will be verified by suitable statistical analysis. The randomization process is performed preoperatively using a closed envelope ('Sealed Envelope') that assigns a patient to one of the two intervention groups.

Eligibility Criteria:
Inclusion Criteria:

* Consent of the adult patient
* Elective laparoscopic-assisted colorectal surgery, elective laparoscopic cholecystectomy, or elective laparoscopic fundoplication

Exclusion Criteria:

* Lack of patient consent
* Pregnancy and breastfeeding
* Allergies to local anaesthetics used
* Infections at the puncture sites
* History of complex abdominal wall reconstruction
* Chronic pain syndrome
* Fibromyalgia
* Chronic opioid use
* Chronic alcohol abuse
* Chronic drug abuse (THC, amphetamines, cocaine, etc.)
* Psychiatric preconditions (depression, schizophrenia, etc.)
* Patients with impaired consciousness, communication, or cognitive function
* Diagnosed coagulopathies (e.g., platelet count \<80,000/µL, PTT/aPTT- prolongation \>1.5 upper normal value)
* Therapeutic anticoagulation