A Comprehensive Review of the Use of Alpha 2 Agonists in Spinal Anesthetics

Abstract

Background: Spinal Anesthesia was the first regional anesthetic technique to be performed. It was performed by Dr. August Bier, known for the Bier block, and his colleagues on August 16, 1898. Dr. Bier opted for, what he referred to at the time as "cocainization of the spinal cord" by introducing 15 mg of cocaine intrathecally prior to the operation. The surgery was largely uneventful and painless. The patient only experienced some vomiting and a headache postoperatively. Dr. Bier's use of neuraxial anesthesia aimed to directly inject local anesthetics in and around the central nervous system (CNS) for more direct control of pain and anesthesia. Local anesthetics were an important discovery in anesthesiology. However, since the advent of local anesthetics and spinal anesthesia as an alternative technique to general anesthesia, much has been learned about both the benefits and adverse effects of local anesthetics. It was quickly learned that use of local anesthetics would be limited by their potential for life-threatening toxic effects. For this reason, there was a push towards development of novel local anesthetics that had a larger therapeutic window with less likelihood of serious side effects. In addition to developing newer local anesthetics, the idea of adding adjuvants provided an opportunity to potentially limit the life-threatening events. These adjuvants would include medications such as epinephrine and alpha-2 agonists, such as clonidine and dexmedetomidine. Other adjuvants include opioids, glucocorticoids, and mineralocorticoids.

Objectives: In this review, we will delve further into the indications, contraindications, uses, mechanisms, and future of spinal anesthesia and its adjuvants.

Study design: A literature review of recent publications in the field of alpha 2 agonists used in spinal anesthetics was carried out from 2015 to present day. Consensus opinions were formulated in various areas.

Setting: This literature review was carried out at various medical universities throughout the nation and Europe.

Limitations: As research has only just begun in this field data is limited at this time.

Conclusions: The use of spinal anesthesia provides a reliable dermatome blockade to facilitate many different surgical procedures. The combination of local anesthetics with opioid medications within the subarachnoid space has been the standard of care. Adjuvant medications like alpha 2 agonists may play a significant role in prolonging spinal blockade as well as limiting cardiovascular complications such as hypotension and bradycardia. The use of alpha 2 agonists instead of opioid medications intrathecally decreases pruritus and delayed respiratory depression. Animal models have demonstrated the synergistic effects of utilizing alpha 2 agonists with opioids in the subarachnoid space. The addition of clonidine to fentanyl and local anesthetic demonstrated a shorter time to neural blockade, but no significant change in duration of the spinal. Interestingly alpha 2 agonists with local anesthetics showed increase block duration compared to opioid with local anesthetics. Further human trials need to be undertaken to analyze the effectiveness of alpha 2 agonists in the intrathecal space, but preliminary data does indicate it is an exemplary alternative to opioids.

Keywords: obstetrics; spinal anesthetics; Alpha 2 agonist.