Dexmedetomidine Versus Clonidine as an Adjuvant to Lidocaine Spinal Anesthesia in an Ovine Experimental Model

Sheep are routinely used as orthopedic models due to their similarities to human joints. Spinal anesthesia provides adequate analgesia for these procedures, and its duration can be enhanced with adjuvant drugs. Clonidine is commonly used in human spinal anesthesia, while dexmedetomidine is a newer and more selective α-2 agonist. This study compared the duration and analgesic effect of these two drugs as adjuvants in spinal anesthesia. Thirty-nine sheep undergoing experimental pelvic limb cartilage damage surgery were enrolled. Animals were sedated with diazepam (0.4 mg kg^-1) and buprenorphine (10 μg kg^-1) intravenously. Propofol was given as needed (0.5 mg kg^-1) and oxygen support via face mask was continuous. Animals were positioned with the treated limb in a dependent position for the lumbosacral spinal block. Sheep were divided into three groups (n = 13), receiving lidocaine 2% (L group), lidocaine 2% + clonidine 20 μg mL^-1 (CL group), or lidocaine 2% + dexmedetomidine 1 μg mL^-1 (LD group) for spinal block (1 mL every 10 kg). Recovery times (minute) from the spinal block were recorded: anal sphincter tone (AS), recovery of sensibility (RoS), first limb movements (FMov), time of standing (ToS), and first rescue analgesia; ataxia (ATA) was also measured after standing. Dexmedetomidine increased the duration of spinal anesthesia, affecting both motor and sensory functions.