Background and Aims

Background and Aims: Various intravenous adjuvants have been used along with spinal anesthesia to delay the onset of postoperative pain, and decrease the analgesic requirement. Intravenous dexmedetomidine and midazolam is known to prolong subarachnoid block. The primary objective was to compare the effects of intravenous dexmedetomidine with midazolam on the duration of spinal anesthesia. Materials and Methods: Forty-three patients presenting for elective infraumbilical surgery under spinal anesthesia were randomly allocated into two groups. Group A received a loading dose of 0.5?gkg-1 of intravenous dexmedetomidine followed by a maintenance dose of 0.5?g/kg/h. Group B received a loading dose of 0.03 mg kg-1 of intravenous midazolam followed by a maintenance dose of 0.03 mg/kg/h. Two dermatomal regressions, regression to S1 level, sedation score, vitals and other complications were noted. Results: The mean time for two dermatomal regressions was significantly prolonged in group A than B (2.3 ± 0.4 h vs.1.6 ± 0.5 h, P=0.001). The mean time for sensory regression to S1 dermatome was also prolonged in group A (5.2 ± 0.83 h vs.4.4 ± 0.87 h, P=0.01). Decrease in heart rate, systolic blood pressure and mean arterial pressure from baseline were comparable at one hour. Glycopyrrolate was administered in 45% of patients in group A and 21% in group B, which was statistically significant(P=0.039). Conclusion:Intravenous dexmedetomidine prolongs duration of spinal anesthesia than intravenous midazolam in patients undergoing infraumbilical surgeries. Its use should be practiced with caution due to a higher incidence of hemodynamic instability.
Key Words: Adjuvants, dexmedetomidine, midazolam, spinal anesthesia

Introduction
Various intravenous adjuvants have been used along with spinal anesthesia to delay the onset of postoperative pain and decrease the analgesic requirement.1 Midazolam is one of the frequently administered sedative agents during subarachnoid block for conscious sedation. Dexmedetomidine is a highly selective alpha 2 agonist with sedative, analgesic and anxiolytic properties.2 It is not associated with respiratory depression which makes it a safe drug for conscious sedation.3 Intravenous dexmedetomidine and midazolam are known to prolong sensory and motor blockade of the subarachnoid block. This study was designed to compare the effects of these two drugs for conscious sedation on patients scheduled for infraumbilical surgery under spinal anesthesia. Previous studies have used higher bolus doses of dexmedetomidine and midazolam,4,5,6 but we have used lower bolus dose of the study drugs with a presumption that it would lead to fewer hemodynamic instability with the same efficacy. The primary objective of this study was to compare the effects of intravenously administered dexmedetomidine versus midazolam on the duration of bupivacaine spinal anesthesia. The secondary objectives were to evaluate the hemodynamic changes caused by intravenous dexmedetomidine and midazolam.
Materials and Methods
This prospective, single-blinded, parallel, randomized controlled study was conducted at the Anesthesiology Department of a tertiary care teaching hospital between June 2017 and February 2018. Approval from the institutional ethics committee (IEC-AIMS-2017-ANES-183) and written informed consent from patients were taken. ASA 1 and 2 physical status patients, between the age group of 18 and 60 years presenting for elective infraumbilical surgery under spinal anesthesia were recruited. Patients on sedative medications/opioids/antidepressants in the week prior to surgery, pregnant patients and patients with heart rate less than 50/minute or fall in mean arterial pressure more than 20% from baseline five minutes after spinal anesthesia were excluded from the study.
All patients received oral premedication of ranitidine 150 mg and metoclopramide 10 mg on the night prior to and on the morning of surgery and alprazolam 0.25 mg on the night prior to surgery. In the operation theatre, pre-induction monitors (non-invasive blood pressure, electrocardiogram and saturation probe) were placed. All the patients were pre-loaded with 10 mL/kg of lactated Ringer’s solution. All patients received oxygen supplementation via facemask at 5 L/min. Sub-arachnoid block with 3 mL of 0.5% heavy bupivacaine was given using standard technique between L3-L4 or L4-L5 space in the lateral position. Patients were randomly allocated into group A and B with the help of a random list generated by computer and opaque sealed envelope method until both groups had 20 or more patients in it. Group A patients received a loading dose of 0.5 ?g/kg of intravenous dexmedetomidine over 10 minutes followed by a maintenance dose of 0.5 ?g/kg/h. Group B patients received a loading dose of 0.03 mg/kg of intravenous midazolam over 10 minutes followed by a maintenance dose of 0.03 mg/kg/h till the end of surgery. The patients were not aware to which group they belonged. Sensory blockade was checked with loss of cold sensation in the midline with spirit soaked cotton balls. Two-dermatomal regression from the maximum level of sensory blockade and regression to S1 dermatome were recorded. Sensory block was assessed in patients every 30 minutes. Vitals such as heart rate, systolic blood pressure (SBP), mean arterial pressure (MAP) and oxygen saturation (SpO2) were recorded immediately after the subarachnoid block and at 5-minute intervals for first 15 minutes and thereafter, at half hourly intervals till two hours after the completion of surgery.
The management of blood pressure changes was according to standard protocol. If the MAP fell more than 20% from the baseline, ephedrine 3 mg IV bolus up to 5 times was administered and after which noradrenaline infusion was started to treat hypotension. Bradycardia defined by an HR less than 50 per minute was treated with intravenous glycopyrrolate 0.2 mg. If bradycardia persisted, it was treated with intravenous atropine 0.6 mg. The level of sedation was evaluated using Ramsay level of sedation scale (1- Anxious, agitated, or restless, 2- Cooperative, oriented, and tranquil alert, 3- Responds only to commands, 4- Asleep, but brisk response to light glabellar tap or loud, 5- Asleep, sluggish response to light glabellar tap or loud auditory stimulus and 6- No response) at half hourly intervals. Patients with a sedation score more than four were excluded from the study after discontinuation of the sedative infusion. At the end of the surgery, patients were shifted to the recovery unit. Time to shift out from recovery to the ward was also noted.
Statistical methods
As there were no similar studies in the existing literature comparing dexmedetomidine and midazolam with the same dosages, a pilot study was conducted to calculate sample size. Based on the mean and standard deviation of time taken for two dermatomal regression of sensory blockade in group A versus B, with 95% confidence and 80% power, the minimum sample size required to obtain statistically significant results with a P value of

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