Motor and sensory blocking effect of intrathecal fentanyl versus dexmedetomidine as adjuvants to bupivacaine for cesarean section

Background
Intrathecal α agonists prolong the duration of action of local anesthetics and reduce the required dose. Dexmedetomidine is an α receptor agonist, and its α/α selectivity is eight times higher than that of clonidine.
Aim
The aim of this study was to determine the effect of adding dexmedetomidine and fentanyl to intrathecal bupivacaine on the onset time and duration and intensity of motor and sensory blocks for cesarean section.
Patients and methods
The study was carried out on 40 adult female patients who were randomly classified using closed envelope method into two equal groups, with 20 patients in each: group D patients received intrathecally 2.5 ml volume of 10 mg (2 ml) 0.5% hyperbaric bupivacaine and 10 µg dexmedetomidine in 0.5 ml (prepared by diluting 1 ml dexmedetomidine in 5 ml of normal saline), and group F patients received intrathecally 2.5 ml volume of 10 mg (2 ml) 0.5% hyperbaric bupivacaine and 20 µg fentanyl in 0.5 ml (prepared by diluting 2 ml fentanyl in 2.5 ml of normal saline). The aim was to evaluate motor and sensory block. Sensory block assessment: the onset and duration of sensory block was assessed by ice cube method, and time taken from intrathecal injection to the highest level of sensory block and sensory regression to the L dermatome were recorded. On achieving T7 sensory blockade level, surgery was allowed. Motor block assessment: onset and degree of motor block was assessed by Bromage scale: 0, no paralysis; 1, inability to raise extended leg; 2, inability to flex the knee; and 3, inability to flex the ankle (complete motor block).
Results
Sensory and motor block onset times were shorter in group D than in group F. The regression of the sensory block to S1 dermatome and Bromage 0 were longer in group D than group F. The two-dermatome regression time was longer in group D than group F. There was a statistically significant decrease in group F regarding systolic, diastolic, and mean arterial blood pressures and heart rate than group D. There was no statistically significant difference among the two groups regarding arterial oxygen saturation and respiratory rate. Neonatal outcome was normal in all groups.
Conclusion
Intrathecal dexmedetomidine addition to bupivacaine for spinal anesthesia synergistically increases block duration and shortens sensory and motor block onset time without any significant adverse effects.