In this study, it was aimed to evaluate the effects of subcostal anterior quadratus lumborum block (S-QLB3) and İntrathecal morphine (ITM) on postoperative acute pain scores and opioid consumption in the first 24 hours after laparoscopic nephrectomy surgery.

For all patients undergoing surgery, analgesic medications and techniques are routinely administered preoperatively, intraoperatively, and postoperatively to relieve their pain. Depending on the method applied, patients' analgesic needs in the recovery room and ward after surgery may vary. In patients undergoing laparoscopic nephrectomy, multimodal analgesia (paracetamol, nonsteroidal anti-inflammatory drugs, and opioids) is routinely applied in our clinic, utilizing various regional techniques or intravenous analgesics .

Opioids are the gold standard for postoperative pain control; however, they increase the incidence of opioid-related adverse effects such as dizziness, nausea, vomiting, constipation, and respiratory depression. Therefore, minimizing opioid use and its side effects is essential for postoperative pain control. Regional analgesia is a beneficial method for reducing opioid consumption and postoperative pain. It may also reduce postoperative morbidity and mortality.

Recently, interfascial plane blocks have been used for postoperative pain control in abdominal surgeries. The quadratus lumborum block (QLB) is a relatively new interfascial plane block technique in which local anesthetics are injected adjacent to the quadratus lumborum muscle. There are four different approaches to the QLB: anterior, intramuscular, lateral, and posterior. Anterior QLB involves the injection of a local anesthetic between the quadratus lumborum (QL) muscle and the psoas muscle. The dermatome coverage is determined by the injection site. The injection of local anesthetic anterior to the QL muscle potentially allows the drug to spread into the thoracic paravertebral space, blocking the somatic and sympathetic nerves of the lower thoracic segments. This situation helps us achieve more effective analgesia in abdominal surgeries.

Intrathecal morphine (ITM) is an emerging strategy for postoperative analgesia following major abdominal surgery. Traditional spinal analgesia protocols often rely on continuous thoracic epidural anesthesia due to their ability to provide adequate analgesia with a few cardiopulmonary complications. However, epidural anesthesia is also associated with more frequent perioperative hypotension, technical failures, increased fluid administration, and longer length of stay (LOS). Therefore, ITM is an attractive alternative because it offers easier administration, potent efficacy at low doses, and reduced postoperative complications, providing a form of spinal analgesia that can be used when epidural catheters are contraindicated.

The analgesic properties of ITM have been demonstrated in recent studies involving cardiac, gynecological, spinal, orthopedic, urological, colorectal, hepatopancreatobiliary, and major abdominal surgeries. With an estimated duration of action of up to 24 hours, these studies have focused on the initial postoperative recovery period and generally found lower pain scores and, in some cases, reduced early postoperative opioid requirements. Intrathecal morphine has been successfully used for postoperative pain in various surgeries. Being a hydrophilic opioid, morphine's limited sequestration in adipose tissue delays its clearance from the cerebrospinal fluid compared to other opioids. As a result, the analgesic effects of intrathecal morphine last longer, providing up to 24 hours of analgesia without the need for indwelling catheters or continuous infusions. Direct injection into the intrathecal space also allows morphine to act directly on opioid receptors in the brain and the substantia gelatinosa of the spinal cord, providing a potent analgesic response.

In this study, it was aimed to determine whether the subcostal anterior quadratus lumborum block (S-QLB3) is non-inferior to intrathecal morphine (ITM) in terms of postoperative 24-hour opioid consumption in patients undergoing laparoscopic nephrectomy.

The H0 hypothesis of study is that the mean difference in postoperative 24-hour morphine consumption between S-QLB3 and ITM is less than or equal to the non-inferiority margin.

Patients will be divided into two groups:

Group S-QLB3:A unilateral S-QLB3 block will be performed (0.4 ml/kg of 0.25% bupivacaine + 1:400.000 adrenaline). In addition, IV morphine-PCA will be applied postoperatively for 24 hours.

Group ITM: Intrathecal morphine will be performed (5 mcg/kg preservative-free morphine (maximum 200 mcg) + 7.5 mg isobaric bupivacaine). In addition, IV morphine-PCA will be applied postoperatively for 24 hours.

Inclusion Criteria:

• 18-70 years who had an American Society of Anesthesiologists (ASA) Physical Status classification I-III

Exclusion Criteria:

• refusal to participate in the study
• body mass index>35 kg/m2
• contraindications to peripheral nerve blocks or spinal anesthesia (e.g., the presence of coagulopathy or pre-existing local or systemic infection etc.)
• unable to perform regional anesthesia because of anatomical deformity
• clinically important cardiovascular and cerebrovascular diseases or preexisting significant organ dysfunction (eg, hepatic, renal or respiratory disorders)
• allergic reaction to any study drugs
• history of substance
• abuse within the three-month period prior to surgery, chronic opioid use for at least a continuous administration of opioids for a duration of 30 days at daily morphine-equivalent dose ≥15 mg/d (1)
• psychiatric illness and disorder in communication.

Sealed opaque envelopes containing study participation numbers will be used to assign each patient. A researcher not involved in patient follow-up will use the web-based;Research Randomizer; (Urbaniak and Plous 2013) tool to give each participation number to a random group with a 1:1 ratio.

A nurse not an active investigator in the study will have each participant choose an envelope containing the study participation number. They will inform the anesthetist who will administer the block/blocks about which group the patient is in immediately before administration. Researchers, patients, surgeons, and nurses will not be aware of the randomization of groups.