A RANDOMIZED CONTROLLED TRIAL TO DETERMINE THE EFFICACY OF PROPHYLACTIC ORAL MIDODRINE IN PREVENTING POST SPINAL HYPOTENSION IN PATIENTS UNDERGOING LOWER LIMB ORTHOPAEDIC SURGERIES

A prospective randomized double blinded comparative study is planned. Pre- anaesthetic evaluation of all patients undergoing lower limb orthopaedic surgery will be performed by an anaesthesiologist a day before surgery. Patients will be kept nil by mouth after midnight and pre medicated with Pantoprazole 40mg orally night before and on the morning of the surgery. An informed, written and valid consent will be taken from 100 patients, who satisfy the inclusion criteria and they will be randomly allocated to two groups according to computer generated randomized number table. Allocation concealment will be done by serially numbered opaque sealed envelope (SNOSE) method. Patients and investigator will be blinded to the study drugs. The study drugs will be administered to patients (Group M and Group P) by anaesthesiologist who will not be taking part in the study. All patients will be screened in the ward before attendance to the theatre by the anaesthesiologist who supervised the administration of tablets. Baseline systolic blood pressure (SBP) and heart rate (HR) are recorded. Patients will be randomly allocated to the following: Group M (n = 50): Midodrine tablets of 10 mg will be given 1 hour before spinal anaesthesia. Group P (n = 50): Placebo tablets (identical to Midodrine tablets) will be given 1 hour before spinal anaesthesia. Intraoperative monitoring includes electrocardiography, non invasive blood pressure, and pulse oximetry. An 18-gauge cannula will be inserted, and 8 mL/kg of lactated ringer’s solution will be given to all patients before performing subarachnoid block. Subarachnoid block will be performed in the sitting position by injecting hyperbaric bupivacaine 15 mg (0.5% hyperbaric bupivacaine 3mL) and 60µg Buprenorphine in L4-5 or L3-4 intervertebral space using a 25-gauge quinke spinal needle. The highest sensory level of the spinal block was tested by the pinprick method, every 5 minutes for 20 minutes and recorded after 20 minutes. Hemodynamic variables such as systolic blood pressure and heart rate were recorded at 2, 5, 10, 15, 30, 45,and 60 minutes after spinal anaesthesia. In addition, these parameters were recorded after deflation of the tourniquet at the end of the surgery. Intraoperative hypotension is defined as decrease in systolic blood pressure to less than 80% of baseline or to less than 90mmHg. It will be treated with 5mg ephedrine IV bolus and increasing infusion rate of lactated ringer’s solution. 5mg ephedrine IV bolus will be repeated if hypotension persists. Severe hypotension (systolic blood pressure less than 80 mm Hg) will be treated with an intravenous bolus of 10mg ephedrine. Symptomatic bradycardia will be treated with intravenous atropine 0.6 mg and repeated if needed. A single measurement of systolic blood pressure or heart rate below the defined level will be sufficient to qualify as hypotension, severe hypotension, and bradycardia. The number of doses of intravenous ephedrine(5mg) and intravenous atropine used to manage intraoperative hypotension and bradycardia will be noted. In the event of episodes of reactive hypertension defined as systolic blood pressure more than 160mmHg will be managed with injection labetalol 5 to 20 mg IV bolus or injection nitroglycerine infusion a the rate of 5 to 20 mcg/kg/min. The primary outcome will be the occurrence of hypotension defined as systolic blood pressure less than 90 mm Hg or less than 80% of baseline, after spinal anaesthesia. Our hypotension outcome is a binary event (yes/no) defined as the occurrence of at least 1 episode for a patient below either threshold, versus none, across the repeated measurements. Secondary outcomes include requirements of ephedrine and atropine, episodes of reactive hypertension (more than 120% of baseline systolic blood pressure), nausea and vomiting, vasovagal attacks, and shivering.