Study sample 1. Data collection for determining ED50 with 95 percent CI will begin with the 3rd cross-over pair. 2. This protocol will be continued for further 7 successes to failure crossovers pairs. 3. Expected sample size of 40 patients. Study protocol All patients will undergo a detailed pre-anaesthetic examination as per the institute protocol at least one day before the surgery. Preoperative investigations including complete hemogram, serum electrolytes and renal function test will be recorded as per standard protocol. In the operating room, standard monitoring as per American Society of Anaesthesiologists recommendation (ECG, pulse oximetry, non-invasive BP) will be done. An 18G IV cannula will be inserted in all patients. Balanced salt solution (RL or Plasmalyte) will be started.
Patients will be positioned for spinal anaesthesia in sitting or lateral position. Preservative-free intrathecal morphine (ITM) along with 1 ml of 0.5 percent bupivacaine (heavy) will be administered prior to induction of general anaesthesia as a single shot injection in the lumbar spine with a 25 G spinal needle under aseptic precautions.
Protocol for dose titration of ITM Dose titration will follow the modified Dixon’s up and down method. Dose for first patient will be 50 mcg of intrathecal morphine ITM diluted in a volume on 1 ml of 0.5 percent heavy bupivacaine. If this dose leads to analgesic failure, subsequent doses will be increased by 25 mcg. Once analgesic success is achieved, subsequent doses will be decreased by 25 mcg till analgesic failure is encountered at which subsequent doses will be again increased by 25 mcg.
Standard induction of general anesthesia will be done as per the preference of the anesthesia team with 2 mcg per kg of IV Fentanyl. Anaesthesia will be maintained with isoflurane and muscle relaxation will be achieved by intermittent boluses or a continuous infusion of intermediate acting non-depolarizing muscle relaxant atracurium. Intraoperative fluid protocol will be decided by the attending anaesthesiologist and the amount of intraoperative fluid administered (crystalloid, colloid, blood and blood products) will be noted. All the patients will be catheterized perioperatively as per surgical protocol.
Intraoperative analgesia protocol Patients will receive 2 mcg per kg IV fentanyl at induction and 1 mcg per kg IV fentanyl bolus whenever there is need for analgesia as deemed by the treating anesthesiologist. Patient will also receive 15 mg per kg IV paracetamol and 0.5 mg per kg IV ketorolac. At the end of surgery, neuromuscular blockade will be reversed, and patient will be extubated. All patients will be closely monitored for 24 hours.
In PACU, standard monitoring consisting of non-invasive blood pressure, ECG, pulse oximetry will be used. Patients will receive 15 mg per kg IV Paracetamol every 6 hours and PCA fentanyl (25mcg IV bolus with lock-out interval of 10 min, maximum 4 hour limit of 400 mcg, with no background infusion).
Postoperative NRS scores will be monitored on awakening from anaesthesia and at 6, 12, 18 and 24 hours. ANALGESIC FAILURE will be defined if the average NRS score more than 4 or patient PCA fentanyl demand more than 4mcg per kg IV at the end of 24 hours. ANALGESIC SUCCESS will be defined if the average NRS score less than 4 or patient PCA fentanyl demand less than 4mcg per kg IV at the end of 24 hours.
During the first 24 hours in the PACU, the occurrence of side effects like nausea, vomiting, pruritus, post-dural puncture headache and respiratory depression will be noted and treated with appropriate therapy.
Respiratory depression will be defined as respiratory rate less than 8 breaths per minute and treated as per the patient’s clinical conditions by the attending anaesthesiologist.
The quality of post-operative recovery will be assessed at the end of 24 hours in PACU using the QoR-15 score. |