Comparison of the Effects of Intravenous Fentanyl and Intravenous Dexmedetomidine on Characteristics of Spinal Anesthesia

Introduction and aim Spinal anesthesia is a widely used technique for lower abdominal and lower limb surgeries, offering effective pain control and muscle relaxation. Various adjuvants have been explored to enhance the quality and duration of spinal anesthesia, with opioids and α-2 agonists being popular choices. Fentanyl, a potent opioid, and dexmedetomidine, a highly selective α-2 agonist, have both shown promising results when used as adjuvants. This study aimed to compare the effects of intravenous fentanyl versus intravenous dexmedetomidine on the characteristics of spinal anesthesia, including onset and duration of sensory block, hemodynamic stability, postoperative analgesia, and side effects. Methods This is a prospective, randomized, double-blind, comparative study involving sixty patients aged 18 to 65 years. The patients were classified as American Society of Anesthesiologists physical status I and II and were scheduled for elective infraumbilical surgery under subarachnoid block. The patients were randomly divided into two groups as follows: group D and group F. Patients of group D received IV dexmedetomidine 0.5 µg/kg and group F received IV fentanyl 1 µg/kg as premedication 5 minutes before spinal anesthesia over 10 minutes. Vital parameters, the onset of sensory and motor block, the highest level of sensory blockade achieved, regression time of spinal anesthesia by two segments, Ramsay sedation score, postoperative numerical rating scale, and time of requirement of first dose of postoperative rescue analgesic were recorded and analyzed. Results Both group D and group F were comparable in terms of age, gender distribution, BMI, American Society of Anesthesiologists (ASA) grading, and type of surgery. The time to achieve T10 sensory blockade was significantly faster in group F (5.5±1.27 minutes) compared to group D (6.5±1.6 minutes, p=0.01). However, the difference between the highest level of sensory blockade achieved and the time to achieve motor blockade was not statistically significant. Group D showed a significantly longer time to two-segment regression of spinal level (141.8±23.5 minutes vs. 94.33±13.6 minutes, p<0.001). Hemodynamic parameters were comparable between groups. Group D demonstrated higher Ramsay sedation scores from 10 minutes to 45 minutes postanesthesia with maximum difference at 15 minutes (p<0.001) and lower pain scores at 4 and 6 hours postsurgery (p=0.02 and p=0.008, respectively). The time to rescue analgesia was significantly longer in group D (6.9±1.5 hours vs. 5.5±0.63 hours, p<0.001). Side effects were minimal and comparable between the two groups. Conclusion While both fentanyl and dexmedetomidine are valuable intravenous adjuncts to spinal anesthesia, dexmedetomidine offers advantages in terms of prolonged sensory block, better postoperative analgesia, and longer time to rescue analgesia. Fentanyl, on the other hand, provides a faster onset of sensory block. Dexmedetomidine produced a slightly higher level of sedation, particularly in the early postanesthesia period. The choice between these two drugs should be tailored to the specific requirements of the surgical procedure and individual patient factors.