Clinical Application and Safety of Intrathecal Adjuvants in Single-Shot Thoracic Segmental Spinal Anesthesia: A Narrative Review.

Thoracic segmental spinal anesthesia (TSSA) is an emerging regional anesthesia (RA) technique. TSSA with local anesthetic (LA) alone is associated with a relatively short duration of surgical anesthesia and postoperative analgesia, which may limit its clinical utility. Intrathecal adjuvants have been widely used in lumbar spinal anesthesia (LSA) to prolong block duration and improve block quality. However, their role in TSSA remains poorly defined. This review summarizes commonly used intrathecal adjuvants during TSSA, their doses, adverse effects, and safety considerations. A comprehensive literature search was performed using PubMed, Europe PubMed Central (PMC), and Google Scholar. Key search terms included "thoracic spinal anesthesia," "thoracic segmental spinal anesthesia," "segmental thoracic spinal anesthesia," "intrathecal adjuvant," "fentanyl," "dexmedetomidine," and "clonidine." A total of 463 relevant articles were identified from PubMed (39), Europe PMC (26), and Google Scholar (398). Finally, 76 articles were selected for the review. An important observation from this review is the growing role of adjuvants in TSSA. Common intrathecal adjuvants in TSSA include opioids and α2-agonists and, less commonly, benzodiazepines, corticosteroids, and N-methyl-D-aspartate (NMDA) antagonists. Several studies reported satisfactory surgical conditions with the preservation of spontaneous ventilation and improved hemodynamic stability. This finding has important implications for high-risk patients with severe cardiopulmonary diseases. Intrathecal adjuvants significantly improve block quality, prolong analgesia, and reduce local anesthetic requirements. Fentanyl and dexmedetomidine are the most extensively studied adjuvants in TSSA; morphine, buprenorphine, and ketamine have also been evaluated in a smaller number of studies and appear clinically useful. However, adverse effects such as hypotension, bradycardia, respiratory depression, and opioid-related complications remain important concerns.