Comparing Intravenous Single Low Doses of Magnesium Sulphate Versus Dexamethasone as Adjuvants to Ultrasound Guided Transversus Abdominis Plane (TAP) Block for Prolongation of Postcesaren Analgesia

Study Setting: Ain shams University maternity Hospitals, Cairo, Egypt. Study Period: 4 months from 1st December 2019 to 1st April 2020. Sampling Method: Random sample Sample Size: 60 patients Study Design A total of (60) full term pregnant women (completed 37 weeks) will be recruited for the study will undergo elective cesarean section. Written informed consent will be obtained from all patients before randomization. Randomization will be done with the help of a computer generated list of numbers. Patients will be divided randomly and equally into three groups (20) Patients each. The first group patients will be assigned to magnesium sulphate group (M), the second group of patients will be assigned to dexamethasone group (D) and the third group will be assigned to placebo group (C). Group assignment, preparation and administration of drugs will be performed by a junior anesthetist who is neither involved nor interested by any means in the study. Blind grouping will be kept to all including the patients themselves, until the completion of study.

Preoperative Anesthetic Assessment All patients will be subjected to a thorough medical history, physical examination with thorough airway assessment, laboratory investigations (fasting blood sugar, kidney, liver function tests, serum electrolytes, coagulation profile, and electrocardiogram) preoperatively. They will be also counseled about the anesthetic management and potential complications of both surgery and anesthesia, and the explanations of numerical pain analogue scale (NAS) from 0-10. All these data will be documented.

Anesthetic Protocol All participants will be admitted to operating theatre (OR) induction area where patient identification is confirmed and an 18-gauge intravenous cannula will be inserted to all Participants. Participants in group (M) will receive 50 mg/kg MgSO4 in 100 ml isotonic saline intravenous (I.V) over 20 minutes prior to induction of general anesthesia by 30 minutes, participants in group (D) will receive 2 mg Dexamethasone in 100 ml isotonic saline IV while participants in group (C) will receive 100 ml isotonic saline IV (placebo) by the same route and over the same duration as control.

General anesthesia will be induced with intravenous propofol 2.0 mg/kg, succinyl choline 1.0 mg/Kg then they will be intubated orally which is fixed after confirmation of its place by capnography and auscultation. Anesthesia will be maintained by 2% sevoflurane in 100% oxygen then atracurium 0.1 mg/kg will be given for maintenance of muscle relaxation. After delivery of the fetus and placenta, 2 mg midazolam, 1 µg/kg fentanyl and 10 IU oxytocin (in 500 ml ringer solution) will be administrated. Immediately after completion of surgery, each patient will receive ultrasound guided bilateral ultrasound guided TAP blocks. After that muscle relaxant will be antagonized by 40 µg/kg neostigmine and 20 µg/kg atropine, then awake extubation will be done and the patients will be transferred to the recovery unit. All patients will be monitored all through the surgery by standard monitors including, electrocardiogram, the pulse oximeter, non-invasive blood pressure, and capnography.

TAP Block Technique Using an 18 G Tuohy needle (80 mm Smiths medical Portex®) and the layers of the abdominal wall will be identified guided by superficial high-frequency 45 mm linear array ultrasound probe (13 MHz) as described by McDonnell and colleagues.(1) Twenty millilitre of 0.25% bupivacaine will be injected slowly after careful aspiration to ensure no vascular injury has occurred. Successful injection will produce an echo-lucent space between the muscle layers (internal oblique and transversus abdominis). All TAP blocks will be performed by the same anesthetist.