Intra-operative Magnesium Sulphate for Post-operative Pain in Patients Undergoing Total Abdominal Hysterectomy Under General Anesthesia

All women who have been planned for total abdominal hysterectomy will be enrolled in the study. Patients who do not meet the inclusion criteria or those who refuse to participate will be excluded from study . Other enrolled patients who meet the eligibility criteria will be randomised and allocated to two study groups- Magnesium (M) group and Control (C) group by computer generated numbers that will be concealed in a sequentially numbered, opaque sealed envelopes. The envelopes will be opened before the surgery begins by a doctor not involved in the study and not assigned to the Gynaecology operating room. The drug will be prepared and labelled study drug as: In group M- Magnesium sulphate @ 50mg/ kg in 100 ml of normal saline and in group C- 100 ml of normal saline. Anaesthetic management, administration of the study drug and any intra-operative changes in vitals requiring treatment will be recorded in the anaesthesia management sheet by another doctor who is assigned to Gynaecology operating room.

A day prior to surgery, eligible patients will be explained in detail about the purpose of study, need, benefits and risks of procedure. The participants will be explained about numerical rating scale (NRS) of pain, how to use it and rate it during post-operative period. Written informed consent will be obtained. The patients will be counselled about fasting protocol and asked to remain nil per oral of 2 hours for clear liquid, 6 hours for light foods and 8 hours for fatty food.

In pre-operative holding area : Baseline vitals systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial blood pressure (MAP), heart rate (HR), respiratory rate (RR), Oxygen saturation (SpO2) will be recorded. Intravenous access will be established with an 18 or 20 gauge cannula. A 3-way stopcock will be attached to the cannula and Lactated Ringer's will be infused @ 100ml/hr.

In the operating room: Standard American Society of Anaesthesiologists monitors will be attached. All patients will be subjected to a standardised anaesthetic protocol. Induction of general anaesthesia, intubation, ventilation parameter set up and maintenance of anaesthesia will be done as per standard anaesthetic practice in our institute.

Meanwhile, at the time of induction, 100 ml of study drug will be infused via side port of 3-way stopcock over 20-30 minutes. Ringer lactate solution will be infused throughout the surgery as per standard practice in our institute. Hemodynamic parameters SBP, DBP, HR, SpO2, RR will be monitored and recorded as per anaesthesia protocol. Additional analgesia during the peri-operative period will be standardised with IV Paracetamol 15 mg/kg post induction and IV Fentanyl 0.5 mcg/kg every hour of intra-operative period and any additional dosing of analgesia will be recorded. Urine output monitoring will be done on hourly basis. If less than 0.5 ml/kg/hr, underlying cause will be looked for, and if no other causes is found, Mg toxicity will be suspected and serum magnesium level will be sent. Meanwhile necessary medical management will be done. Post operative nausea and vomiting (PONV) prophylaxis will be standardised in both groups of patient. IV Ondansetron 4mg single dose 15 to 20 minutes before extubation will be given. 0.25% Bupivacaine not exceeding 2 mg/kg dose will be administered locally at the site of surgical incision at the end of surgery. Reversal of muscle relaxation and extubation will be done as per attending anaesthesiologist. Patient will be transferred to recovery room.