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

## TL;DR

This study compares how two drugs, clonidine and dexmedetomidine, affect spinal anesthesia in sheep, finding that dexmedetomidine prolongs the effects more.

## Contribution

The study provides new empirical evidence on the comparative efficacy of dexmedetomidine versus clonidine as adjuvants in spinal anesthesia in an ovine model.

## Key findings

- Dexmedetomidine prolonged spinal anesthesia effects more than clonidine in sheep.
- Both drugs improved pain control during orthopedic surgery in the model.
- Dexmedetomidine caused longer postoperative loss of mobility and sensitivity compared to clonidine.

## Abstract

This study compared the effectiveness of two drugs, clonidine and dexmedetomidine, in enhancing the effects of spinal anesthesia. Spinal anesthesia is a technique used to block pain in the lower part of the body during surgery, and it is applied both in people and in sheep undergoing orthopedic procedures on the hind limbs. To make this technique last longer and work more effectively, additional drugs—called adjuvants—are sometimes added. Clonidine and dexmedetomidine belong to a group of drugs called α-2 agonists, which reduce nervous system activity and can improve pain control. This study evaluated the impact of these two drugs on pain relief and mobility. Our findings showed that both drugs provided good pain control during orthopedic surgery. However, dexmedetomidine resulted in a more prolonged loss of sensitivity and mobility in the postoperative period than clonidine. Understanding these differences can help veterinarians and researchers choose the most suitable adjuvant depending on the type of surgery and the expected recovery time. This knowledge may also contribute to refining spinal anesthesia protocols and improving animal welfare in both clinical and experimental settings.

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.