Anterior Quadratus Lumborum Block as a Component of Multimodal Analgesia for Abdominal Hysterectomies

Primary outcomes : intraoperative fentanyl consumption, daily requirement of morphine and pain level (with visual analogue scale - VAS) after surgery. Secondary outcomes: quality of recovery after anesthesia (with QoR-15 questionnaire), heart rate perioperatively, mean arterial pressure perioperatively, incidence of postoperative nausea.

Thromboprophylaxis will be administered based on the risk of thromboembolic complications for all patients. In the operative room all patients will receive ondansetron, dexamethasone and tranexamic acid. Patients will be told that they will receive multimodal analgesia but they won't know if they get a regional component (quadratus lumborum block). The randomisation will take place in the operative room. After general anesthesia induction and endotracheal intubation attending anesthesiologist will leave the operative room and anesthesiologist-resident will perform randomization and QL-block or won't perform QL-block. Thus participants and attending anesthesiologist won't know the randomisation result. In our study attending anaesthesiologist will be the researcher who will collect and analyse data. After the intubation patients of the control group will receive acetaminophen 1000 mg, dexketoprofen 50 mg before incision and MgSO4 1250 mg with ongoing continuous infusion of MgSO4 2500 mg per hour. In addition to these analgesia regimen patients in the II (QL) group will receive bilateral ultrasound-navigated anterior quadratus lumborum block before the start of the surgery. The investigators will use a convex low-frequency transducer with a frequency of 1.5-5 Mhz (General Electric Logiq e ultrasound machine). The block will be performed in the patient's spine position. Investigators choose anterior approach hypothesizing its superiority over other approaches to quadratus lumborum block. After proper visualization and obtaining an adequate sonographic image, the 22g needle will be inserted through the lateral abdominal wall and will be advanced through the skin, subcutaneous fat tissue, external oblique muscle, internal oblique muscle, aponeurosis of the transverse abdominis muscle, then it will be advanced through the quadratus lumborum muscle and operator will reach thoracolumbar fascia, between the quadratus lumborum muscle and the psoas major muscle. In this localization anesthesiologist-resident will inject a local anesthetic. Operator will use 20 ml of 0,25% bupivacaine with 4 mg of dexamethasone as adjuvant for one side, all blocks will be performed bilaterally only. General anaesthesia will be maintained by continuous propofol infusion with target effect site concentration 3-3,5 mcg/ml, atracurium infusion with target effect site concentration 900 ng/ml and bolus fentanyl injections to maintain target effect site concentration 2-4 ng/ml. All target concentrations will be calculated via ITIVA version 6.3.2 software. Attending anesthesiologist will modify the dosage of anesthetic drugs, particularly fentanyl, reducing them if necessary. At postoperative stage for patients of both groups investigators plan to administer multimodal analgesia: dexketoprofen (150 mg/day), acetaminophene (4000 mg/day). In addition, in the case of severe pain - morphine will be added (5-20 mg/day).

Mechanical ventilation will be performed in pressure-regulated volume control ventilation mode counting tidal volume 6 ml/kg (Getinge Flow-e anesthesia machine). Intraoperatively attending anesthesiologist will count the fentanyl consumption considering that the length of the surgeries will not have significant differences.

At the end of the surgery investigators will count total amount of administered fentanyl, evaluate heart rate and mean arterial pressure.

After the end of the surgeries patients will be extubated and transferred to the postoperative ward. After the surgery investigators are planning to evaluate morphine consumption, level of pain according to the visual analogue scale (VAS), quality of recovery after anesthesia (with QoR-15 questionnaire), heart rate, mean arterial pressure, incidences of nausea.