Alpha 2 agonists in regional anesthesia and analgesia.

Clonidine is a partial alpha 2 adrenergic agonist that has a variety of different actions including antihypertensive effects as well as the ability to potentiate the effects of local anesthetics. It can provide pain relief by an opioid-independent mechanism. It has been shown to result in the prolongation of the sensory blockade and a reduction in the amount or concentration of local anesthetic required to produce perioperative analgesia. Different routes for the administration of regional anesthesia, including intravenous, intrathecal and epidural ones, as well as the addition of clonidine for peripheral neural blockade, have been described. It has been also used for intra-articular administration. The latest articles describing the use of clonidine in regional anesthesia are discussed. Most authors agree that the use of clonidine for regional neural blockade in combination with a local anesthetic results in increased duration of sensory blockade with no difference in onset time. The addition of clonidine to the local anesthetic opioid mixtures seems to produce analgesia of longer duration, more rapid onset and higher quality. The higher doses of clonidine were associated with a more cephalad spread of the spinal blockade and increased sedation and hypertension. When clonidine is added to a fentanyl-bupivacaine mixture for epidural labor analgesia, it seems to provide satisfactory analgesia of a longer duration than that produced by the fentanyl-bupivacaine combination alone. Similar results were found when epidural analgesia using levobupivacaine with clonidine was used in patients undergoing total hip arthroplasty. Less clear results were seen when clonidine was used for caudal anesthesia in a pediatric patient population. The addition of clonidine to intravenous regional anesthesia resulted in prolongation of the tourniquet time and improvement of postoperative analgesia. However, the latter was found to be short-lived. In another study, the effects of clonidine used for intra-articular administration in combination with morphine were investigated. These authors found a significantly higher rate of satisfaction in the group of patients receiving clonidine plus morphine. Although several recent studies have shown certain benefits from the use of clonidine for regional anesthesia, further investigations are necessary to clarify its role.